1. Introduction

Emotion regulation has been broadly defined as the monitoring, evaluation and modifying of emotional reactions in order to accomplish goals (Thompson, 1994). This can include both implicit emotion regulation, i.e. processes which occur automatically and largely outside conscious awareness and occur at very early stages of the emotion regulation process, and explicit emotion regulation, which involves using conscious strategies to modify emotional responses (Gyurak et al., 2011). Fully functional emotion regulation requires the ability to recognise the emotional significance of perceived stimuli, to appreciate the need for regulation, and then to select and implement an appropriate strategy (Sheppes et al., 2015). As such, it requires the co-ordination of multiple high-level processes including executive functions (Kesek et al., 2009) and in some cases social cognitive skills such as perspective taking.

Adolescence (approximately spanning the ages 10–19; Sawyer et al., 2012) is of considerable interest from an emotion regulation perspective for several reasons. Developmentally, this period is associated with significant biological and physical changes, a growing need for independence, academic and employment pressures and fluctuating social relationships (Casey et al., 2010). These challenges are often accompanied by increased emotional reactivity and stress. As will be discussed in more detail below, it has been hypothesised that ongoing brain development renders adolescents less able to successfully regulate their emotions, putting them at greater risk for anxiety and stress related disorders (Powers and Casey, 2015). Indeed the period of adolescence has been associated with an increasing incidence of internalising and externalising symptoms (Lee et al., 2014, Paus et al., 2008, Spear, 2000). This suggests that adolescents may be particularly vulnerable to emotional dysregulation, although it is worth noting that, as with adults, it can be difficult to distinguish whether these behaviours result from poor regulation, increased affective responses, or both.

Cognitively, high-level executive and social processes needed for emotion regulation, including working memory, inhibitory control, abstract thought, decision making and perspective taking, all undergo development during adolescence (e.g. Blakemore and Robbins, 2012, Dumontheil, 2014, Sebastian et al., 2010a, Somerville and Casey, 2010). Development of these cognitive processesappears to be underpinned by structural and functional development at the neural level, particularly in the protracted development of parts of prefrontal cortex and the remodelling of connections between prefrontal and limbic regions (see below). Simultaneously, adolescents are learning to negotiate increasingly complex social contexts (Sebastian et al., 2010a, Vartanian, 2000). It is possible that the interactions between these neurocognitive processes and social pressures could contribute to the observation that aspects of adolescent emotional processing and regulation development appear to follow a non-linear trajectory. In turn, this may at least partially explain increased emotional volatility and risk taking at this stage of life relative to both adulthood and earlier childhood (Casey and Caudle, 2013). Adolescence may therefore be a critical phase for the development of adaptive emotion regulation, with long-term consequences for future regulatory success and mental health. It has been suggested that adolescence is a period of heightened learning and flexibility (Casey et al., 2008, Steinberg, 2005). It could therefore be a critical phase for the development of adaptive emotion regulation strategies and in turn the implementation of interventions. Targeting this window of opportunity could have positive long-term consequences for mental health (Wekerle et al., 2007).

This review will present mounting behavioural and neural evidence on the development of implicit and explicit emotion regulation in adolescence, and will highlight potential research directions. We will first briefly discuss the structural development of brain regions involved in the detection, expression and regulation of emotion across adolescence (see Blakemore, 2012, Giedd, 2008, Giedd and Rapoport, 2010, Lenroot and Giedd, 2006, Paus, 2005 for more comprehensive reviews of adolescent structural brain development). We will then review human behavioural and neuroimaging data investigating the development of different aspects of emotion regulation, ranging from automatic implicit emotional control (e.g. the ability to filter out emotional information via attentional control mechanisms) through to explicit and effortful strategy use. This section of the review will broadly follow the Process model of emotion regulation (e.g. Gross, 1998), and the recent Extended Process model (Sheppes et al., 2015). fMRI evidence suggests that, while conceptually quite different, there may be continuities in the way these implicit and explicit processes are instantiated at the neural level (e.g. Drabant et al., 2009). It is worth noting that due to the existence of other comprehensive reviews in the field (Blakemore and Robbins, 2012, Casey and Caudle, 2013, Steinberg, 2008) we will not cover risky decision-making, although emotion regulation abilities doubtless play a role here.

2. Adolescent Brain Development: Relevance to Emotion Regulation

Adolescence is characterised by a period of heightened emotional reactivity, instability and risk-taking. Several studies using self-report questionnaires have found hypersensitivity to peer rejection and peer influence in adolescents relative to adults and children (Kloep, 1999, Larson and Richards, 1994, O’Brien and Bierman, 1988). Moreover, in a longitudinal study it was found that average emotional states over a week became more negative across early adolescence but this decline in emotions ceased by late adolescence (18 years of age) (Larson et al., 2002). Stability of daily emotional states also increased with age. Increased emotional reactivity has also been demonstrated in behavioural studies where experimental ostracism has been manipulated. In one study, overall mood was found to be significantly lower after ostracism in the adolescent group and state anxiety was higher in the young adolescent group (12–14 years of age) but there were no differences between conditions on either measure for adults (Sebastian et al., 2010a). Adolescents also place a higher emphasis on rewards, particularly social rewards, compared to adults which may make the perceived benefits outweigh the perceived risk (Reyna and Farley, 2006, Steinberg, 2008).

Over the past few decades, neuroimaging studies have begun to suggest that ongoing structural and functional brain development during adolescence may contribute to adolescent-specific behaviours. Evidence suggests that structural brain development in brain regions subserving emotion regulation continues into adulthood (Paus et al., 2008). For example, the prefrontal cortex (PFC), is central in the generation and maintenance of emotion regulation strategies (Ochsner and Gross, 2008; and see below). Subdivisions of the PFC most implicated in emotion processing and regulation include the dorsolateral (dlPFC), ventrolateral (vlPFC) and ventromedial regions (vmPFC) (Kalisch, 2009, Ochsner and Gross, 2008; see Box 1). Development of the PFC is particularly protracted, with reductions in cortical grey matter volume, density and thickness continuing into adolescence and even into the third decade of life (Gogtay et al., 2004, Shaw et al., 2008).

These reductions are thought to index a maturational process. One theory is that they correspond to synaptic pruning, i.e. the elimination of redundant synapses (Blakemore, 2008). Post-mortem studies have shown that synaptic density gradually increases during childhood, peaks in early adolescence, and then reduces by roughly 40% during adolescence and early adulthood before stabilising, following an inverted-U shaped pattern (Huttenlocher and de Courten, 1987). This synaptic pruning in adolescence fine-tunes the remaining connections into specialised functional networks, which might result in more efficient cognitive processing (Blakemore, 2008). However, others have suggested that a reduction in the number of synapses during adolescence is unlikely to have such a large effect on cortical volume as measured by MRI, as cortical grey matter contains numerous cellular elements including neural cell bodies, axons, dendrites, glial cells and blood vessels. Instead, grey matter decline may reflect an artefact of increased myelination of intra-cortical axons (Bourgeois and Rakic, 1993, Paus, 2005, Paus et al., 2008). Unfortunately, methodological limitations make it difficult to directly link developmental change in the living brain as measured with structural MRI with changes in the underlying cellular anatomy.

Subcortical and limbic regions are heavily involved in emotion generation and regulation, and also show developmental change during adolescence. For example, the amygdala increases in volume between the ages of 7.5 and 18.5 years (Schumann et al., 2004). Moreover the amygdala has vast connectivity with several regulatory regions, for example ventral and dorsal pathways connect the amygdala to prefrontal brain regions such as the medial and lateral orbitofrontal cortices, as well as anterior cingulate cortex (ACC) and dlPFC (Bracht et al., 2009, Johansen-Berg et al., 2008). Structural connections between these regions continue to mature during adolescence, resulting in greater top-down control, and strengthening pathways that are called upon routinely (Gee et al., 2013). This improved connectivity is largely a result of a linear increase in white matter volume and density in adolescence; however, this decelerates into adulthood (Giedd et al., 1999, Ostby et al., 2009, Tamnes et al., 2013). Developmental changes in white matter are thought to reflect ongoing axonal myelination, increasing the efficiency of neurotransmission between brain regions (although see Perrin et al., 2009, for a discussion on sex differences in the maturation of white matter; specifically they found age-related increases in axonal calibre in males and increased myelination in females, suggesting a more complex developmental picture).

Together, these structural findings show that regions of the brain involved in emotion generation and regulation continue to develop during adolescence and beyond, and that adolescence may represent a time of particular plasticity for functions underlain by these circuits. They also show that structural development does not always occur linearly over time within brain areas, with quadratic and cubic trajectories often evident (e.g. Mills et al., 2014, Shaw et al., 2008), nor does it occur uniformly across multiple brain regions. Instead, we see that different brain regions that network together to implement emotion processing and regulation develop at different rates within the same individual, with connectivity between these regions also in flux. It has been suggested that this may have functional consequences, particularly for socioemotional processing and behaviour during adolescence, when the bulk of this development occurs. It should be noted however that we currently know relatively little about how the very well-characterised structural brain development occurring during adolescence influences brain function and subsequently behaviour.

Nonetheless, several testable models of links between adolescent brain and behaviour have been suggested. For example, several researchers have posited a ‘developmental mismatch’ or ‘imbalance’ between neural systems supporting emotional reactivity and regulation such that during adolescence the development of prefrontal regions lags behind that of limbic structures such as the amygdala, ventral striatum (VS) and orbitofrontal cortex (OFC) (e.g. Casey et al., 2008, Somerville and Casey, 2010, Steinberg, 2008). As a result, during the time lag in functional maturity between prefrontal and limbic regions, adolescents are less effective at regulating their own emotions and are more affected by emotional context (e.g. peer influence) when making decisions. Most recently, the ‘Triadic Systems Model’ (Ernst, 2014), has been developed, which posits an imbalance between three key systems: PFC (involved in regulatory control), striatum (involved in approach behaviours) and amygdala (involved in avoidance). Unlike the dual-system models mentioned above, it highlights the importance of both approach and avoidance and proposes different patterns of functioning within these three systems during adolescence relative to adulthood. These differences can be quantitative, with different age groups engaging regions more strongly or extensively than other age groups, and/or qualitative, with a shift in dependence on one set of brain regions to another. Moreover the model posits that the three systems mature along different timelines, and that this asynchrony, combined with less mature connectivity across brain regions, may be implicated in adolescent risk taking.

While these models all have in common the idea that behaviour indicative of poor emotion regulation in adolescence is due (at least in part) to the relative immaturity of the PFC and its connections relative to regions involved in more basic emotional responses, this notion has been criticised (Pfeifer and Allen, 2012). Contrary to these models, several studies have not consistently found heightened amygdala responses to emotional stimuli during adolescence (McRae et al., 2012, Pfeifer et al., 2011, Vasa et al., 2011). Moreover studies have shown that heightened VS responses are associated with adaptive functioning such as decreases in risky behaviour, increased resistance to peer influence and reductions in negative affect following social exclusion (Pfeifer et al., 2011, Masten et al., 2009). Additionally, diminished VS (and increased prefrontal) responses to reward anticipation and outcome have been associated with lower daily self-reported positive affect and higher depression in typically developing adolescents (Forbes et al., 2010). The developmental mismatch models therefore may oversimplify the link between adolescent brain development and behaviour.

One way in which these models have been refined and developed is with the integration of hormonal factors. For example Crone and Dahl's (2012) model suggests that pubertal hormone changes influence the limbic system, which contribute to social and affective changes. These social and affective influences interact with cognitive-control systems that can lead to flexibility in the engagement of frontal cortical systems in adolescents, depending on the motivational salience of the context. The interaction of these two processes is generally adaptive and developmentally appropriate to the learning demands of adolescence. However, some situations – perhaps through interactions between individual risk factors and risk environments – can contribute to negative consequences such as substance misuse or depression.

Typically, in cognitive neuroscience, a cognitive function is first well-characterised by behavioural experiments. Models based on these are then further tested using neuroscientific techniques to characterise the neural bases of these functions and refine cognitive models where possible. In the study of adolescent emotion regulation, research has followed a different paradigm. The discoveries in the past 15 years or so regarding ongoing and uneven neural development during adolescence have led to a revival of interest in the development of the functions underpinned by these regions. Functional neuroimaging studies have been used to investigate isolated emotion regulatory functions during adolescence, but until recently behavioural work on adolescent emotion regulation has been surprisingly scarce (Adrian et al., 2011). Luckily, this is now changing as the neuroimaging studies have provided a context for behavioural research (therefore the discussion of studies in this review will follow this sequence). Moreover, adolescent emotion regulation research is also beginning to benefit from the large body of practical and theoretical work on adult emotion regulation to have emerged over the past two decades. Below, influential adult models of emotion regulation are discussed in order to provide a framework for data addressing the development of emotion regulation during adolescence.

3. Models of emotion regulation: relevance to adolescence

There are many strategies for regulating emotional responses, and the most prominent approach to organising these has been to focus on the time point at which regulatory processes are brought to bear on emotion-evoking situations. The “process model” of emotion regulation (Fig. 1a) theorises that emotion generation and appropriate regulatory processes unfold in a particular sequence over time (Gross, 1998, Gross, 2014). The first two processes – situation selection and situation modification – both help to shape the situation to which an individual will be exposed. A situation that is emotionally salient gives rise to early emotional reactivity (i.e. intense involuntary reaction to an emotional situation, coupled with a generation of emotional responses such as attentional bias and heightened physiological responses). This emotional reactivity tends to be implicit in nature and therefore occurs before conscious awareness. As awareness increases, the individual actively selects which situation they will place themselves in and modifies its emotional impact (e.g. by shortening exposure time). Situation selection is commonly seen in psychopathology, e.g. where an individual with social anxiety disorder avoids social situations to regulate their emotions (Wells and Papageorgiou, 1998). Attentional deployment is then used to focus attention away from aspects of the situation that provoke undesired emotions. The emotional situation is then explicitly appraised and evaluated, either by engaging in cognitive change such as reappraisal (i.e. reinterpreting the meaning of the situation to reduce its negative impact) or response modulation, which refers to direct attempts to influence physiological, experiential or behavioural emotional responses once they already have been elicited. For example, exercise and relaxation techniques may be used to decrease physiological and experiential effect of negative emotions (Oaten and Cheng, 2006). One of the most researched forms of response modulation is expressive suppression, which entails inhibiting emotional expressions (Gross, 2002). The process model also contains a feedback loop, recognising that emotional responses can modify the situation that gave rise to the response in the first place, and suggesting that the emotion generation process can occur recursively, is ongoing, and dynamic (Gross and Thompson, 2007). The processes identified in this model can be thought of as existing on a continuum from implicit to explicit emotion regulation: as awareness of emotional reactivity increases, regulation becomes more explicit. However, it is difficult to pinpoint the threshold at which regulation becomes explicit, as this likely varies between individuals and contexts.

It has been noted, however, that while the process model focuses mainly on implementation success (or failure) of particular emotion regulation strategies, adaptive emotion regulation actually involves a broader repertoire of skills, including flexible strategy selection (e.g. Bonanno and Burton, 2013). This has led to the recent development of an ‘extended process model’ (Gross, 2014, Sheppes et al., 2015, see Fig. 1b). This posits that emotion regulation occurs in three stages: (1) Identification, in which an emotional state is identified and the decision over whether or not to regulate this is made; (2) Selection, in which an appropriate regulatory strategy is selected and (3) Implementation, in which the strategy is implemented (corresponding to the original process model). Each stage involves perception of the state of the world, valuation as to whether this is positive or negative, and then action based on the valuation stage. For example, at the Identification stage, an individual might perceive that they are experiencing a negative emotion, evaluate that this exceeds a given threshold of negative affect and that regulation is required, and therefore decide to take action to select an appropriate strategy. This then feeds into the Selection stage, where the full range of regulatory strategies are perceived and evaluated, and appropriate action is taken.

When taken in relation to models of adolescent brain development, the extended process model raises several questions. At each stage, does the perception–valuation–action cycle unfold in the same way as in adults, or are there developmental differences? It might be posited, for example, that if social approval is particularly rewarding (Blakemore and Mills, 2014), a hedonic state elicited in the presence of peers may not trigger the valuation of a need to regulate in the Identification stage. Equally, however, adolescents might be hypothesised to show immaturities at the Selection stage. A wide range of regulatory strategies have been identified (see Table 2 for a list of explicit/deliberate strategies), but adolescents may not have access to the same range as adults, either because they are unaware of particular strategies, because they have not had sufficient practice in using them, or because certain strategies require advanced executive function (Hofmann et al., 2012) and/or social cognition (Gross, 2014) skills, which continue to develop during adolescence. If these skills are not fully developed, adolescents may not be able to select from the range of strategies available to adults, or may select a strategy that they are unable to implement effectively. Executive function development may also impact the ability to switch flexibly from one strategy to another during Selection, if the original strategy proves ineffective.

The role of executive function and social cognition skills may also play an important role in the Implementation stage. For example, the strategy of reappraisal (cognitively changing one's interpretation of an emotion-eliciting situation) requires that executive functions such as working memory and verbal fluency are in place (Hofmann et al., 2012), but perhaps more importantly that individuals are able to take another person's perspective (Gross, 2014). If a teacher is short with a student, a classic reappraisal response would be to think that perhaps the teacher was just having a bad day. However, there is considerable evidence that the ability to take another person's perspective undergoes protracted development at both behavioural (e.g. Dumontheil et al., 2010) and neural (e.g. Pfeifer and Blakemore, 2012) levels. The following sections will review evidence for the continued development of emotion regulatory processes and their neural bases during adolescence, including the contribution of component executive and social skills where applicable. To date, the vast majority of research has focused on the Implementation stage, i.e. participants are given a strategy and the effectiveness of implementation is measured. However, where possible, reference to Identification and Selection will be made.

These sections will be broadly divided into implicit and explicit processes, as the paradigms used to investigate these are quite different. However, it is noted that this distinction may be too simplistic and that the boundaries between implicit and explicit emotion regulation are likely porous. For instance, Gyurak et al. (2011) proposed that implicit emotion regulation may develop from the habitual use of specific explicit strategies. For example, explicitly reminding oneself that an angry coworker had a bad day may over time lead to the same regulation process occurring implicitly, without awareness.

4. Implicit emotion regulation: neural bases and development in adolescence

Implicit emotion regulation is defined as “any process that operates without the need for conscious supervision or explicit intentions, and aims at modifying the quality, intensity, or duration of an emotional response” (Koole and Rothermund, 2011, p. 1). While this definition does encompass the automatic and habitual use of strategies generally considered explicit as discussed above, this section will focus on regulatory processes that occur at the very earliest stages of emotion perception and processing, and which occur even when individuals are unaware of feeling a subjective emotional response. Emotional stimuli capture our attention (see Carretié, 2014 for a review), particularly via the activation of limbic regions such as the amygdala, which initiates an orienting response to salient stimuli (Gamer and Büchel, 2009). This can be adaptive as such stimuli are particularly likely to require action (e.g. to avoid a dangerous situation), although a hallmark of disorders such as depression and anxiety is a tendency for exaggerated capture by negative and disorder-relevant stimuli (Eysenck and Derakshan, 2011, Williams et al., 1996). However, emotional stimuli in the environment are also often irrelevant, and interfere with our current goals. Regulatory processes typically involving prefrontal circuitry are therefore brought online automatically in order to downregulate limbic responses, particularly when the presentation of emotional stimuli has the potential to interfere with a concurrent executive task. A recent meta-analysis of interactions between emotional stimuli and cognitive control in adults highlighted the involvement of ACC, inferior frontal junction, dlPFC and posterior medial OFC (Cromheeke and Mueller, 2014).

It is therefore no surprise that executive functions are frequently relied upon during emotion regulation as one needs to remember goals, anticipate outcomes, and plan and execute responses (Zelazo and Cunningham, 2007). Accordingly, adult studies have shown that executive functions, such as greater verbal fluency, are associated with greater ability to down-and up-regulate emotions (Gyurak et al., 2009, Gyurak et al., 2012). A recent study investigating this in adolescence has found similar results. Using self-report questionnaires, Lantrip et al. (2015) found that better executive functions were associated with greater use of reappraisal, while reliance on suppression was associated with poorer executive functions such as poorer inhibitory control, problem solving and organisation skills. The findings suggest that the boundaries between executive functions and emotion regulation are quite porous, with executive functions subserving regulation of cognitive and well as emotional processes.

Consequently, tasks used to measure executive functions have also been adapted to assess emotion regulation. The go/no-go task is frequently used to study attention and inhibitory control. In this task, participants are required to either respond and press a button when certain stimuli appear (Go), or withhold their response when a particular target stimulus appears (No-Go). As Go trials are more common, the task measures one's ability to inhibit a prepotent response. When participants perform this task in the presence of emotional stimuli (e.g. when the no-go stimulus is emotional) greater implicit emotion regulation is required as emotion interferes with cognitive control (i.e. the stopping response). Therefore, slower reaction times on Go trials, or greater false alarm rates (responding on No-Go trials) indicate poorer emotion regulation performance.

Another task that measures inhibitory control and attentional bias is the Stroop test (Stroop, 1935) in which participants are required to name the colour of ink in which an item is printed, while attempting to ignore the item itself. Research has continuously found that it takes participants longer to name the colours when the base items are antagonistic colour names than when they are rows of meaningless stimuli (van Maanen et al., 2009). An adaptation of this is the emotional Stroop task where participants name the ink colour in which emotional and neutral words are written. Emotional words, particularly negative words most salient to an individual (e.g. cleanliness-related words in obsessive compulsive disorder), capture attention and lead to reaction time interference relative to neutral stimuli (see Williams et al., 1996 for a review). Like the go/no-go task, implicit emotion regulation here is defined as the ability to maintain cognitive control in the presence of emotional words.

Several functional neuroimaging studies have been conducted using variations of these tasks (summarised in Table 1) to investigate the neural bases and developmental trajectory of implicit emotion regulation in adolescence. For example in a variation of the go/no-go task, Hare et al. (2008) (Table 1) found that children (aged 7–12) and adolescents (aged 13–18) were slower than adults when responding to fearful target (‘go’) faces, implying that they were less efficient at overriding affective interference compared with adults, particularly when asked to override what might be considered a prepotent response to avoid (as opposed to approach) fearful faces. Neurally, adolescents showed exaggerated amygdala activity relative to both children and adults across target and non-target expressions (although this exaggerated response habituated with repeated exposure to the stimuli), providing evidence of a non-linear developmental trajectory of amygdala response, possibly in line with ‘developmental mismatch’ accounts.

This study has been followed up by several behavioural and fMRI studies examining adolescent development in more detail. Tottenham et al. (2011) used a version of this task with 100 participants aged 5–28. Emotion regulation performance was defined as the false alarm rate on no-go trials using emotional face stimuli, since these trials required inhibitory control to be performed in the presence of emotion. More generic cognitive control was defined as false alarm rate on neutral no-go trials. Both emotion regulation and cognitive control improved with increasing age, but importantly the discrepancy between the two decreased with increasing age, i.e. adults showed a smaller difference in performance in withholding responses in the presence of emotion relative to neutral faces than did children or adolescents.

An fMRI study using a variant of this go/no-go task with only appetitive (happy face) and neutral calm face cues found that the false alarm rate on no-go ‘happy’ trials relative to no-go neutral trials was disproportionately greater for adolescents (aged 13–17) than for either children (aged 6–12) or adults (18–29) (Somerville et al., 2011). This adolescent-specific performance dip was paralleled by heightened activity in the VS, an area involved in the processing and anticipation of rewards (Schultz, 2006). Conversely, activation in the inferior frontal gyrus (IFG; typically activated during inhibitory control (e.g. Aron et al., 2004), decreased with increasing age for no-go relative to go trials, and was positively correlated with overall no-go false alarms. Connectivity analyses between IFG and striatum also showed age differences: children showed reduced functional coactivation between these regions on happy no-go relative to happy go trials, compared with adolescents and adults, while adolescents showed increased coactivation between dorsal and VS relative to both children and adults. The neural mechanisms at play during adolescence seem to support the models discussed above: when required to regulate behaviour, adolescents may be driven disproportionately by subcortical signalling, (which shows a non-linear, inverted U-shaped response with age), in the presence of a functionally immature prefrontal regulatory system.

In each of the above studies, the emotional content of the stimuli was relevant for task performance, i.e. participants at least needed to be able to distinguish between emotional and calm faces before making a go vs. no-go decision, if not overtly recognise the precise emotion displayed. Facial expression recognition continues to develop in adolescence, with the ability to categorise different expressions developing at different rates; for example, categorisation of happy faces develops earlier than fear (Durand et al., 2007, Thomas et al., 2007). This factor may at least partially contribute to developmental differences seen in this version of the emotional go/no-go task, or influence the results in an unpredictable manner. There have been a couple of recent studies that have instead looked at inhibitory control in the context of task-irrelevant emotion.

Sticking with facial expression stimuli, Cohen Kadosh et al. (2014) used an emotional go/no-go task variant known as the Overlap task (Bindemann et al., 2005; Table 1) to compare groups of early (aged 11–12) and late (aged 17–18) adolescents. On go trials, the young adolescent group was disproportionately slowed by fearful faces relative to happy and neutral faces, as compared with the late adolescent group. This was interpreted as indicating poorer attentional control in the presence of fear in early adolescence, possibly underlain by continuing maturation of dlPFC. It could be that this group were more likely to have their attention captured by the fearful faces; or that they had more difficulty disengaging from these faces once attention had been captured. Another possible interpretation is that arousal caused by the fearful faces interfered with the decision-making component of the task (i.e. right/left decision), even if attention was appropriately allocated. Interestingly, unlike the emotional go/no-go task discussed above, no age differences were seen for either go or no-go accuracy, perhaps suggesting that age differences in inhibitory control during adolescence are less apparent when emotion is task-irrelevant. This interpretation is supported by a recent study which directly compared go/no-go task versions where emotion was relevant vs. irrelevant in participants aged 6–25, and found that only task-relevant emotion had a strong effect on inhibition (Schel and Crone, 2013).

However, it could also be that the development of inhibitory control in the presence of emotion during adolescence is particularly subtle and follows a non-linear trajectory, rendering it necessary to sample relatively large numbers of participants across the adolescent age range in order to see development. This approach was taken in a recent study by Cohen-Gilbert and Thomas (2013)(N = 100) which employed a go/no-go task in which task-relevant letters were presented at the centre of task-irrelevant background images portraying negative, positive, neutral or scrambled scenes. Slower reaction times were found across all age groups for negative trials. However, lower accuracy on no-go trials in the presence of negative images was seen specifically in adolescents aged 13–14 years (and in girls aged 15–16). Thus, negative emotional inputs appear to disrupt regulatory efforts more easily in early-mid adolescence even when the emotional information is not directly relevant to the task. A shortcoming of using this type of stimuli is that the images are visually less well-matched as compared to facial stimuli. Nonetheless age-related developments in emotion-related inhibitory control measured by this task show parallels with behavioural and neuroimaging data discussed above for the emotional go/no-go task in which emotion is task-relevant. It is interesting to speculate as to why task-irrelevant emotion impacted inhibitory control in this task but not others. Possibly negative pictures and scenes are more emotionally arousing than negative facial expressions; alternatively, the use of finer grained age distinctions enabled subtle age differences to emerge.

Another approach to studying the development of inhibitory control in the context of emotion is to induce emotional states in participants. In one developmental fMRI study, 20 participants aged 5–11 and 25 adult controls engaged in a go/no-go task in which they gained and lost points towards a desired prize (Perlman and Pelphrey, 2011). The task was designed such that participants lost all of the points they had previously won, in order to induce negative emotions of frustration. Five-to-11-year-olds and adults displayed distinct patterns of ACC and amygdala activation when emotion regulation was required; for example, children showed reduced amygdala response when recovering from emotional frustration, while adults showed the reverse pattern. Connectivity analyses showed that as frustration (and thus regulation demands) increased, effective connectivity between the ACC and amygdala also increased. Importantly, this connectivity increased with age in the children, suggestive of ongoing neural maturation underlying this process between childhood and early adolescence. This study did not specifically explore development on this task across adolescence. However, Lewis et al. (2006) (Table 1) conducted an event-related potential (ERP) study using a similar task with 58 participants aged 5–16 years. They found an increased response associated with inhibitory control (the N2 component) in adolescents but not children in response to a negative emotion induction (point loss). These findings suggest that differing cortical regions are involved in emotion regulation as children mature into adolescence.

In early- and mid-adolescence, peer relationships are particularly salient: individuals show an increased sensitivity to acceptance and rejection by peers (Brown, 2004, Nelson et al., 2005, Sebastian et al., 2010a), and an increase in awareness of others’ opinions (Parker et al., 2006, Vartanian, 2000). On the basis of this, Sebastian et al. (2010b) used a rejection-themed emotional Stroop task with fMRI, and found that mid-adolescents (aged 14–16) showed attenuated right vlPFC responses relative to adults during the processing of rejection-related words compared with neutral and acceptance words. This finding is in line with the above theories suggesting that prefrontal regulatory regions continue to develop between mid-adolescence and adulthood. Emotion was task-irrelevant and the requirement to regulate emotion was implicit. However, it is possible that this task tapped into immaturity in prefrontal mechanisms that contributes to hypersensitivity to rejection in adolescence; particularly, as will be seen below, there is considerable overlap in the prefrontal regions recruited during implicit and explicit social rejection tasks.

An emotional variant of the Stroop task has also been used to investigate the development of prefrontal control in late adolescence (ages 18–19) compared with early adulthood (23–25 years; Veroude et al., 2013). Adults activated dorsomedial PFC and precuneus to a greater extent than late adolescents in the presence of negative stimuli (e.g. ‘death’) compared with neutral words (e.g. ‘chair’). While the right vlPFC (inferior frontal gyrus) region identified above as showing age differences in the rejection-themed emotional Stroop did not differentiate between age groups in response to emotional stimuli in this study, left inferior frontal gyrus did show reduced activation in the late adolescents in a non-emotional contrast. This study demonstrates that the maturation of regulatory mechanisms involved in the implicit processing of emotional (and non-emotional) information continues even between late adolescence and the early twenties. This time period (approximately 18–23: ‘emerging adulthood’) is receiving increasing empirical attention in efforts to link identity and role change occurring at this time with continuing neural maturation.

While inhibitory control has so far received the most empirical attention in relation to implicit emotion regulation, there is also evidence for ongoing development of interactions between working memory and emotion processing. Ladouceur et al. (2009) (Table 1) used an emotional n-back task in which participants viewed a continuous stream of items and determined whether each item matched the stimulus presented n stimuli before, in the presence of flanking emotional or neutral faces. In this behavioural study, performance of participants (aged 8–27 years) was examined on trials with neutral and fearful faces as emotional distracters and varying in working memory load (i.e., 2-back versus 0-back condition). Age was negatively correlated with reaction times on 2-back trials in the presence of fearful distracters, i.e. participants became faster with age. However, this effect only held across participants high in trait anxiety. The role of individual differences in emotion regulation and relevant traits during adolescence is discussed in more detail in Section 6 in relation to psychopathology.

Together, these behavioural and neuroimaging studies illustrate specific implicit emotion regulation processes that continue to develop from childhood through adolescence and into adulthood, and deliver insights into their neurocognitive developmental trajectories. Reaction time and accuracy data across tasks show general improvement in the ability to resist interference by emotion between adolescence and adulthood (e.g. Cohen Kadosh et al., 2014, Tottenham et al., 2011) however, some studies have found evidence of a non-linear trajectory, with increased interference in mid-adolescence compared with earlier childhood (e.g. Cohen-Gilbert and Thomas, 2013). Neuroimaging evidence is suggesting that the mechanisms underlying these effects are largely in line with developmental mismatch and triadic model accounts of adolescent development. Studies have shown increased limbic responses to emotional stimuli (e.g. Hare et al., 2008), reduced prefrontal control (e.g. Sebastian et al., 2010b, Veroude et al., 2013), and altered or reduced connectivity between these systems (e.g. Somerville et al., 2011) during adolescence. Thus, there is considerable evidence that the ability to filter out emotional stimuli entering the processing stream in a ‘bottom-up’ manner (Gyurak et al., 2011) in pursuit of a goal continues to mature throughout adolescence. The following section will examine whether similar evidence is available for the development of explicit regulatory processes.

5. Explicit emotion regulation

Explicit emotion regulation strategies require conscious effort during initiation, and some level of monitoring during implementation (Gyurak et al., 2011). As discussed above, explicit strategies of cognitive reappraisal (reinterpreting emotion-eliciting scenarios in a more positive light) and expressive suppression (reducing the outward display of an emotional reaction) have received the most empirical attention, both in adolescence and in emotion regulation research in general. In a recent study by Lantrip et al. (2015) although it was found that reappraisal use was associated with better executive functions in a group of adolescents (aged 12–18), there were no age related differences in strategy use. However, the sample size of this study was relatively small (N = 70) in comparison to a longitudinal study of 1128 adolescents (Gullone et al., 2010). Using a similar self-report method Gullone and colleagues found that suppression use decreases between the ages of 9 and 15. Suppression is generally considered a maladaptive strategy, with reliance on this strategy associated with reduced ability to repair negative moods and decreased experience of positive affect (Gross and John, 2003). Therefore, this reduction in use in this age range makes theoretical sense, as individuals gain the experience and underlying executive and social skills to develop alternative strategies (John and Gross, 2004).

By the same logic, we would predict that use of the more adaptive reappraisal strategy would increase over this time; however, evidence to date has been mixed. Contrary to predictions, Gullone et al. (2010) found an overall decrease in the self-reported use of this strategy in everyday life between the ages of 9 and 15. However, results using a lab-based reappraisal paradigm suggest development in the ability to successfully use reappraisal, at least when instructed to do so (Silvers et al., 2012). Forty-four participants aged 10–23 viewed negative and neutral IAPS pictures and rated their current strength of negative affect on a 4-point scale when either instructed to ‘look’ at the picture and give their natural response, or ‘decrease’, i.e. use reappraisal as trained prior to the experiment. Regulation success was defined as percentage decrease in self-reported negative affect on ‘decrease’ trials relative to ‘look’ trials for negative stimuli, and was found to improve with age, following both linear and quadratic trends. It is worth noting significant methodological differences between these two studies that could explain the discrepant findings, including different age ranges, sample sizes and operationalisations of reappraisal (frequency vs. success). Studies which combine self-reported and experimental measures of reappraisal use and success across the adolescent age range are therefore needed (see Box 2 ‘Outstanding Questions’). While there is research on adults investigating this, there are still many confounds involved such as the different methods used and the timescales in which frequency and success are measured. More research is needed to assess real-world sampling of emotion regulation success over longer time periods both in adults and adolescents (see McRae, 2013, for a discussion on future directions).

Neuroimaging studies of explicit emotion regulation strategies in adolescence have recently begun to investigate age differences in both spontaneous and instructed regulatory processes. In a study by McRae et al. (2012) participants aged 10–22 years completed a reappraisal task similar to that reported by Silvers et al. (2012) above, whilst undergoing fMRI. A linear increase in cognitive reappraisal ability was found with age (in line with Silvers et al., 2012) and this was accompanied by a concomitant age-related increase in left vlPFC. As discussed above, this brain region has been implicated in cognitive control processes in both emotional and non-emotional contexts, and is also associated with cognitive reappraisal in adults (Ochsner and Gross, 2005, Ochsner and Gross, 2008). When participants were not specifically asked to reappraise (i.e. during an unregulated emotional response) adolescents (aged 14–17 years) showed less activation in brain areas associated with social cognition, such as medial prefrontal, posterior cingulate and temporal regions than did either children (aged 10–13 years) or emerging adults (aged 18–22 years). However, these regions were activated to a greater extent during reappraisal (i.e. a regulated emotional response) in adolescents compared to the other age groups. The authors interpreted this as suggesting that adolescents may not automatically engage in these social cognitive processes during unregulated responding, but are able to do so when specifically instructed. However, these inferences should be treated with some caution. The study did not directly test whether social cognitive processes were indeed responsible for activation in these regions (although this is a reasonable assumption based on previous studies); and it is further unknown whether activation of these regions during passive viewing in the children and emerging adults truly constituted spontaneous regulation.

Studies have also looked at the development of reappraisal in the regulation of appetitive cravings for unhealthy foods (Silvers et al., 2014, Giuliani and Pfeifer, 2015). In a recent study, females aged 10–23 were asked to use reappraisal to reduce cravings (Giuliani and Pfeifer, 2015). Across all participants reappraisal engaged regions commonly activated during self-regulation such as the vlPFC and the ACC. While there was a lack of age-related changes in reappraisal success, activation in the right IFG was found to be positively correlated with age, suggesting that older participants may have needed to work harder to regulate their desires for unhealthy food. The authors state however that the age-related changes seen in the reappraisal of negative emotion may not be as pronounced in the reappraisal of food craving.

Given theories linking emotional behaviours in adolescence to maturational processes in underlying brain structure, it makes sense to examine the relationship between structural maturation and successful development of regulatory strategies. This approach was taken in a recent longitudinal study (Vijayakumar et al., 2014), in which 92 participants underwent structural scans at ages 12 and 16, and reported their usage of reappraisal and suppression at age 19. Greater cortical thinning in left dlPFC and vlPFC over the course of adolescence was associated with greater use of reappraisal at age 19, but only in female participants. The direction of the result is in line with the idea that cortical thinning indexes maturation (e.g. Shaw et al., 2008, Tamnes et al., 2013), and thus may underpin more efficient usage of regulatory processes reliant on these brain regions. While it is unclear why the effect was specific to females, the authors suggest that peak cortical thickness may have been reached by the first time point in females but not males, meaning that continuing increases in cortical thickness could have obscured in males the pattern that was observed in females. Studies of reappraisal in adults have also shown that females may recruit prefrontal regions to a greater extent than males (McRae et al., 2008): maturation of the prefrontal regions of interest studied here may therefore be of greater relevance for females than males.

As is the case for adult emotion regulation research, the majority of behavioural and neuroimaging studies in adolescents have focused on strategies that are most tractable for use in the laboratory, namely reappraisal and suppression. However, some researchers have argued that focusing on specific strategies may be problematic for understanding the everyday use of a broad range of explicit emotion regulation strategies (Aldao and Nolen-Hoeksema, 2013). One recent experience sampling study (Heiy and Cheavens, 2014) identified approximately 40 strategies that adult participants (aged 18–31) reported using over the course of the study for the regulation of both negative and positive states (summarised in Table 2). Indeed it is often necessary to regulate positive as well as negative states, e.g. one may wish to upregulate positive responses by savouring a recent happy experience, or conversely downregulate positive reactions if they are socially inappropriate, e.g. schadenfreude.Table 2. The range of explicit emotion regulation strategies used in everyday life by young adults (adapted from Heiy and Cheavens, 2014, with author permission). Experience sampling methods have shown that adolescents also use many of these strategies (e.g. Silk et al., 2003); although as yet it is unclear whether adolescents have access to the same breadth of strategies as adults, or how adolescents recognise the need for regulation and select particular strategies. It is possible that these processes may relate to neural maturation associated with underlying executive function and social cognitive skills.

Experience sampling methods have been used for some time to investigate emotion regulation in adolescence. For example, Silk et al. (2003) asked adolescents (aged 12–15) to provide multiple reports about the intensity, lability, and strategies used to regulate their naturally occurring emotional experience throughout the day across one week. Adolescents also completed self-report measures of adjustment. It was found that adolescents who reported using disengagement (e.g. denial, avoidance, escape, or wishful thinking) or rumination strategies to regulate their emotions were associated with higher levels of depressive symptoms and externalising behaviours. It is worth considering whether it may be possible to incorporate aspects of this more ecologically valid approach with neuroimaging techniques to understand emotion regulation in typical adolescence. As will be seen in the following section, several studies have taken an important step in this direction, linking neural responses as measured in the laboratory with evidence of emotion regulation and dysregulation in everyday life in relation to psychopathology. As discussed above, adolescence is associated with increased emotional reactivity and the developmental trajectory of certain brain areas may render adolescents less able to regulate their emotions effectively, putting them at greater risk of internalising and externalising problems. Examples from the internalising (depression) and externalising (conduct problem) literature will be given in the following section.

6. Emotion regulation, the adolescent brain and adolescent psychopathology

6.1. Internalising symptoms

Psychopathology associated with internalising symptoms notably increases during the adolescent years (Lee et al., 2014, Paus et al., 2008). Major depressive symptoms rise drastically from around 2% in early adolescence (ages 13–15) to 15% in middle adolescence (ages 15–18) (Hankin et al., 1998). In addition, adolescents classified as having internalising problems such as depression have been shown to score highly on the use of maladaptive emotion regulation strategies such as self-blame and rumination, whilst obtaining low scores on reappraisal use (e.g. Garnefski et al., 2005). Recent neuroimaging studies have therefore attempted to shed light on mechanisms underlying poor emotion regulation in adolescent depression.

Neuroimaging studies of explicit emotion regulation in depressed adolescents have largely focused on reappraisal, where this group are known to exhibit behavioural deficits. Studies of instructed reappraisal in depressed adults have found reduced dlPFC response and reduced PFC–amygdala coupling relative to healthy controls (e.g. Erk et al., 2010), in line with findings in typical adults that successful reappraisal relies on the ability of regions including dlPFC, dACC and vlPFC to downregulate emotional responses in amygdala, VS and insula (Ochsner et al., 2012). However, to date, fMRI studies of reappraisal in depressed adolescents suggest a different pattern. Perlman et al. (2012) compared 14 adolescents with depression and 14 controls (aged 13–17) on a task requiring participants to either ‘maintain’ or ‘reduce’ emotional responses to negatively valenced images. During the ‘maintain’ condition, the authors found increased amygdala response and decreased PFC–amygdala connectivity in the depressed adolescents relative to controls, in line with predictions. However, this pattern did not hold for the ‘reduce’ condition: conversely, greater connectivity was found in depressed adolescents when instructed to ‘reduce’. This suggests that dysregulation of PFC–limbic circuitry may contribute to adolescent depression under some circumstances (in this case the instruction to ‘maintain’), but that this is not necessarily a constant marker in adolescent depression.

A similar pattern of results was seen in an fMRI study using a more ecologically valid ‘chatroom’ task in which social stress is created by participants being rejected by virtual peers, relative to being accepted (Guyer et al., 2009). Adolescents are likely to encounter peer rejection in everyday life, and may show greater sensitivity to its effects than do adults (Sebastian et al., 2010a). It has further been argued that rejection may play a special role in the aetiology of adolescent depression, with reciprocal relationships developing over the course of adolescence between social rejection and depressive symptoms (Platt et al., 2013). Platt et al. (2015) instructed 15 depressed and 15 non-depressed adolescents aged 15–17 to either ‘attend’ or to ‘reappraise’ instances of social rejection. Both groups were able to implement reappraisal, reducing negative affect in response to rejection; however, the depressed group showed increased connectivity between right frontal pole and regions including amygdala and hippocampus, specifically during reappraisal. Together, the two extant studies of reappraisal in adolescent depression raise the possibility that mechanisms underlying poor emotion regulation may not be identical to those in adult depression. However to date there have been no studies directly comparing depressed adolescents and adults on emotion regulation abilities in the same sample. Platt et al. (2015) speculate that this increased connectivity during instructed reappraisal may reflect an ability for depressed adolescents to address their pre-existing emotion regulation deficits using cognitive strategies, and suggest that reappraisal training may therefore represent a particularly fruitful avenue for treating adolescent depression. This is an intriguing possibility, but will require additional studies with larger samples to confirm. Another possibility is that depressed adolescents need to engage regulatory mechanisms to a greater extent to achieve the same behavioural effect.

There have also been several studies which have looked at the neural bases of typical adolescent responses to peer rejection in the absence of an explicit instruction to regulate (Guyer et al., 2009, Masten et al., 2009, Sebastian et al., 2011), although participants are fully aware of being rejected and of the negative emotions generated, meaning participants may use explicit regulatory strategies spontaneously. One longitudinal fMRI study explored relationships between neural responses to social rejection and depressive symptoms one year later in 20 13-year olds (Masten et al., 2011). This study used the ‘Cyberball’ paradigm (Williams et al., 2000), in which participants play an online ball tossing game and are unknowingly systematically included or excluded at particular points during the game by the experimenter. Responses in the subgenual ACC predicted depressive symptoms at follow-up. This region was of particular interest given evidence that heightened activity here has been associated both with depressive symptoms (Saxena et al., 2003) and with heightened responses to peer rejection in typically developing adolescents (Masten et al., 2009). Future work could investigate whether instructed strategies such as reappraisal could influence the responsivity of this region in adolescent depression.

6.2. Externalising symptoms

While conduct disorder sometimes onsets before the age of 10 (childhood onset), the majority of externalising symptoms, which include physical aggression, theft, destruction of property and truancy, emerge during adolescence (Moffitt, 1993). Aggressive behaviour is often categorised as either reactive or proactive: reactive aggression refers to aggression triggered by external provocation or frustration, and is associated with poor executive function (Giancola et al., 1996) and impulsivity (Raine et al., 2006); whereas proactive aggression refers to aggression used instrumentally in pursuit of a goal, and is associated with psychopathic traits in adulthood (Patrick, 2001) and callous–unemotional traits in childhood/adolescence (Frick et al., 2003). Poor emotion regulation is thus particularly associated with reactive as opposed to proactive aggression (Eisenberg et al., 2010), although reactive and proactive aggression are moderately correlated and proactive aggressors often display low frustration tolerance.

Neuroimaging studies have only recently begun to investigate conduct problems in adolescence, and early studies in this area have not differentiated between subtypes (e.g. Herpertz et al., 2008). One study which did differentiate groups of adolescents with conduct problems on the basis of low vs. high levels of callous–unemotional traits found that low levels of such traits (i.e. those whose aggressive behaviour is more reactive in nature) were associated with amygdala hyperactivity in response to fearful faces presented implicitly, i.e. below the level of conscious awareness (Viding et al., 2012). This study illustrated inherent overreactivity in response to emotion at the very earliest levels of processing, suggested to be due to an attentional orienting response effect (Gamer and Büchel, 2009, Moul et al., 2012). This is likely to have downstream consequences that contribute to poorly regulated behaviour, since hypervigilance to threatening stimuli is a hallmark of many psychological disorders including anxiety (Richards et al., 2014) and post-traumatic stress disorder (Dalgleish et al., 2001), as well as reactive aggression (Dadds et al., 2006). However, this study did not target regulatory mechanisms specifically.

Sebastian et al. (2014) tested an overlapping sample of adolescents with conduct problems on an implicit emotion regulation task in which participants made a perceptual decision (is a blue dot present or absent?) in the presence of fearful or calm faces. Importantly, when the blue dot was present, it was either presented in the eye region of the face (a particularly salient region for interpreting fear cues: Adolphs et al., 2005) or elsewhere in the face. Adolescents with conduct problems and low callous–unemotional traits (reactive-aggressive subtype) were disproportionately slowed in making the dot/no dot decision in the presence of fearful eyes relative to typically developing controls; and slower reaction times in the presence of fearful eyes in this group were associated with increased left amygdala response. This group also showed increased neural responses during the presentation of fearful eyes in subgenual ACC and OFC relative to controls; two regions involved in directing attention to affective stimuli (Zikopoulos and Barbas, 2012) and integrating emotion and cognitive control (Pessoa, 2008). These findings suggest that emotion may disproportionately interfere with executive processes in adolescents with reactive-aggressive conduct problems, although future studies could additionally examine interactions between prefrontal and limbic circuitry to uncover more detail as to the mechanisms of poor implicit emotion regulation in this group.

If ineffective prefrontal-limbic control is important in the aetiology of reactive aggression, then we might predict that improvement in symptoms would be accompanied by improvement in cortical function. Lewis et al. (2008) investigated this hypothesis using the frustration-inducing emotional go/no-go task described in Section 4) in an ERP study with 27 participants aged 8–12 with mixed externalising an internalising symptoms and 15 typically developing controls. Participants completed the task before and after a 14-week community intervention involving elements of cognitive behavioural therapy and parent management training. Following treatment, children who showed behavioural improvement also showed a normalisation of their N2 ‘inhibitory control’ response, generated by ventral frontal regions, while non-responders did not. Interestingly, the normalisation seen was actually a reduction in N2 amplitude. The authors suggest that previously this group had relied on an inflexible, threat-focused regulatory style which generated a strong N2 response. While still preliminary, this study illustrates that interventions designed to reduce externalising and internalising symptoms may concomitantly help to normalise neural mechanisms tapped by implicit emotion regulation tasks. It is potentially interesting to ask whether the reverse would hold true, for example whether training neural circuits involved in implicit (or explicit) emotion regulation would lead to downstream positive consequences for behaviour.

7. Conclusions

The development of emotion regulation during adolescence has enjoyed a recent surge in interest, largely prompted by discoveries over the past 15 years or so regarding ongoing adolescent development of the cortical and subcortical circuitry underpinning regulatory processes. This review brings together models concerning the structural and functional development of the adolescent brain with models of emotion regulatory processes. It is likely that development continues to occur in processes underpinning all three stages of the extended process model, namely Identification, Selection and Implementation. However, the majority of behavioural and neuroimaging work to date has focused on Implementation. There is some evidence that both behavioural and neural responses during implicit emotion regulation tasks such as emotional go/no-go task variants develop in a non-linear manner, with mid-adolescents showing exaggerated responses to emotion compared with younger and older individuals. This would support models suggesting that non-linear structural brain development has consequences for brain function and adolescent behaviour. However, not all studies show this pattern, and it is unlikely that links between brain structure, brain function and behaviour will be straightforward. For example, even if brain and behaviour are shown to follow similar developmental trajectories for a given function, this does not necessarily mean that one trajectory causes the other (Pfeifer and Allen, 2012). Regarding explicit strategies such as reappraisal, some studies show an increase in the use of this strategy over adolescence, in line with theories suggesting that reappraisal use should increase as underlying executive, verbal and social cognitive skills develop. However, others suggest that instructed use may not be paralleled by increasing spontaneous use with age in everyday life. As there are still relatively few studies in the area, methodological differences across studies make it difficult to draw overall conclusions. These include whether emotion is relevant or irrelevant to task performance, whether particular strategies are instructed or not, how tasks are adapted for neuroimaging, and sample age range and size. As more empirical work becomes available, an important next step will be to synthesise evidence through the use of meta-analysis. Some outstanding research questions are listed in Box 2. Of most practical relevance will be work delineating relationships between the neural bases of emotion regulation and the emergence and prevention of psychopathological symptoms. The plasticity of the adolescent brain at this time could yield opportunities for positive intervention before symptoms escalate to clinical levels.

Link to Article

1. Introduction

Emotion regulation encompasses the intricate processes of monitoring, evaluating, and modifying emotional reactions to achieve desired goals (Thompson, 1994). This multifaceted construct encompasses both implicit and explicit emotion regulation. Implicit emotion regulation refers to automatic, unconscious processes occurring in the early stages of emotional response generation. Conversely, explicit emotion regulation involves conscious strategies employed to modulate emotional experiences (Gyurak et al., 2011). Effective emotion regulation necessitates the ability to discern the emotional significance of stimuli, recognize the need for regulation, and select and execute appropriate strategies (Sheppes et al., 2015). This complex interplay of cognitive processes includes executive functions (Kesek et al., 2009) and, in certain instances, social cognitive skills like perspective-taking.

Adolescence (roughly ages 10–19; Sawyer et al., 2012) presents a compelling period for examining emotion regulation. This developmental stage is characterized by significant biological, physical, and social changes, including increased autonomy, academic demands, and fluctuating social dynamics (Casey et al., 2010). These challenges frequently coincide with heightened emotional reactivity and stress. It is hypothesized that ongoing brain development during adolescence may limit the capacity for successful emotion regulation, potentially increasing the risk of anxiety and stress-related disorders (Powers & Casey, 2015). Adolescence is marked by a higher incidence of internalizing and externalizing symptoms (Lee et al., 2014; Paus et al., 2008; Spear, 2000). This suggests a particular vulnerability to emotional dysregulation during this period, though disentangling the contributions of poor regulation and heightened affective responses remains a challenge.

Cognitively, adolescence is a time of significant development in executive functions and social cognitive processes essential for emotion regulation. This includes advancements in working memory, inhibitory control, abstract reasoning, decision-making, and perspective-taking (e.g., Blakemore & Robbins, 2012; Dumontheil, 2014; Sebastian et al., 2010a; Somerville & Casey, 2010). These cognitive refinements are thought to be underpinned by structural and functional brain development, particularly in the prefrontal cortex and its connections with limbic regions. Concurrently, adolescents navigate increasingly complex social environments (Sebastian et al., 2010a; Vartanian, 2000). The interplay between these neurocognitive advancements and social pressures may contribute to the non-linear developmental trajectory observed in aspects of adolescent emotional processing and regulation. This, in turn, may partially explain the heightened emotional volatility and risk-taking observed during this stage compared to both adulthood and earlier childhood (Casey & Caudle, 2013).

Adolescence, therefore, represents a critical window for the development of adaptive emotion regulation, with potential long-term implications for future emotional well-being and mental health. This period of heightened learning and flexibility (Casey et al., 2008; Steinberg, 2005) underscores the importance of understanding the development of emotion regulation strategies and potential interventions.

This review examines the burgeoning behavioral and neural evidence on implicit and explicit emotion regulation development during adolescence and highlights potential research avenues. We first provide a concise overview of structural brain development in regions implicated in emotion detection, expression, and regulation during adolescence (for comprehensive reviews, see Blakemore, 2012; Giedd, 2008; Giedd & Rapoport, 2010; Lenroot & Giedd, 2006; Paus, 2005). Subsequently, we delve into human behavioral and neuroimaging data exploring the development of various emotion regulation facets, ranging from automatic, implicit control (e.g., attentional filtering of emotional information) to effortful, explicit strategy use. This section aligns with the Process model of emotion regulation (e.g., Gross, 1998) and the more recent Extended Process model (Sheppes et al., 2015). Existing fMRI evidence suggests that despite their conceptual distinctions, implicit and explicit processes may share neural substrates (e.g., Drabant et al., 2009). Notably, we do not delve into risky decision-making, as comprehensive reviews already exist (Blakemore & Robbins, 2012; Casey & Caudle, 2013; Steinberg, 2008). Nonetheless, the role of emotion regulation in risky decision-making is acknowledged.

2. Managing Emotions as the Brain Develops

Adolescence is marked by heightened emotional reactivity, instability, and risk-taking tendencies. Self-report studies consistently reveal increased sensitivity to peer rejection and influence among adolescents compared to adults and children (Kloep, 1999; Larson & Richards, 1994; O’Brien & Bierman, 1988). Longitudinal data indicate that while average emotional states decline during early adolescence, this trend stabilizes by late adolescence (around 18 years of age; Larson et al., 2002). This increased reactivity is mirrored in behavioral studies employing experimental ostracism. For example, adolescents exhibit lower mood and higher state anxiety following ostracism compared to adults, who show no significant changes (Sebastian et al., 2010a). Furthermore, adolescents place greater emphasis on rewards, particularly social rewards, potentially leading to risk-taking behaviors driven by perceived benefits outweighing perceived risks (Reyna & Farley, 2006; Steinberg, 2008).

Neuroimaging studies suggest that ongoing structural and functional brain development during adolescence contributes to these age-specific behaviors. Structural brain development in regions subserving emotion regulation extends into adulthood (Paus et al., 2008). For instance, the prefrontal cortex (PFC), particularly its dorsolateral (dlPFC), ventrolateral (vlPFC), and ventromedial (vmPFC) subregions, plays a crucial role in generating and maintaining emotion regulation strategies (Kalisch, 2009; Ochsner & Gross, 2008; see Box 1). PFC development is protracted, with gray matter volume, density, and thickness continuing to decline through adolescence and into the third decade of life (Gogtay et al., 2004; Shaw et al., 2008).

These reductions in gray matter are thought to reflect maturational processes, potentially synaptic pruning—the elimination of redundant synapses to optimize neural circuitry (Blakemore, 2008). However, other interpretations, such as increased myelination of intracortical axons, have been proposed (Bourgeois & Rakic, 1993; Paus, 2005; Paus et al., 2008). Disentangling these possibilities remains a methodological challenge.

Subcortical and limbic structures, heavily involved in emotion generation and regulation, also undergo significant developmental changes during adolescence. For instance, the amygdala, implicated in processing emotional salience, exhibits increased volume between 7.5 and 18.5 years of age (Schumann et al., 2004). Amygdala connectivity with regulatory regions, including the orbitofrontal cortex, anterior cingulate cortex (ACC), and dlPFC, strengthens during adolescence (Bracht et al., 2009; Johansen-Berg et al., 2008). These structural refinements, attributed to increased white matter volume and density, enhance top-down control and strengthen frequently used pathways (Gee et al., 2013). This white matter development, thought to reflect ongoing axonal myelination, improves the efficiency of interregional neurotransmission (Perrin et al., 2009).

In summary, brain regions implicated in emotion generation and regulation undergo significant development throughout adolescence, suggesting a period of heightened plasticity. However, this development is neither linear nor uniform across brain regions. Instead, regions within the same individual develop at different rates, with their interconnectivity also in flux. These dynamic changes likely have functional implications for socioemotional processing and behavior during this developmental period.

Several models attempt to bridge the gap between adolescent brain development and behavior. The "developmental mismatch" or "imbalance" model posits that prefrontal regions mature later than limbic structures (e.g., amygdala, ventral striatum (VS), orbitofrontal cortex (OFC); Casey et al., 2008; Somerville & Casey, 2010; Steinberg, 2008). This purported lag in prefrontal maturity renders adolescents more susceptible to emotional influences and less effective at regulating emotional responses, particularly in emotionally charged contexts. The more recent "Triadic Systems Model" (Ernst, 2014) emphasizes the interplay between the PFC (regulatory control), striatum (approach behavior), and amygdala (avoidance behavior). This model acknowledges the importance of both approach and avoidance motivations and proposes age-related differences in the functioning of these systems, characterized by quantitative and qualitative shifts in regional engagement and connectivity.

While these models offer compelling frameworks, it is crucial to acknowledge their limitations. Some studies have challenged the notion of heightened amygdala reactivity during adolescence (McRae et al., 2012; Pfeifer et al., 2011; Vasa et al., 2011) and highlighted the adaptive role of VS responses (Pfeifer et al., 2011; Masten et al., 2009). Incorporating hormonal influences, Crone and Dahl (2012) propose that pubertal hormonal changes impact the limbic system, contributing to social and affective changes. These, in turn, interact with developing cognitive control systems, leading to greater flexibility in frontal cortical engagement depending on the motivational context.

The study of adolescent emotion regulation has often deviated from the traditional cognitive neuroscience approach where behavioral characterization precedes neuroscientific investigations. The focus on brain development during this period has fueled research into the functions these developing regions support. Consequently, functional neuroimaging has taken center stage, while behavioral work, until recently, has been relatively scarce (Adrian et al., 2011). This imbalance is gradually being addressed, with neuroimaging findings providing valuable context for behavioral investigations. Moreover, adolescent emotion regulation research benefits from the extensive theoretical and empirical work conducted on adult populations.

3. Adolecent Emotional Regulation

Emotion regulation encompasses a diverse array of strategies, often categorized based on their temporal relationship to emotion-eliciting situations. The "process model" (Gross, 1998, 2014; see Figure 1a) proposes a sequential unfolding of emotion generation and regulation.

The first two processes, situation selection and situation modification, involve shaping the emotional landscape. Emotionally salient situations elicit early emotional reactivity, often characterized by intense, involuntary reactions and physiological responses. As awareness increases, individuals can actively select and modify the emotional impact of situations (e.g., by limiting exposure time). Attentional deployment further allows individuals to shift focus away from emotionally provocative aspects. Explicit appraisal and evaluation then occur, engaging cognitive change strategies like reappraisal (reinterpreting the situation) or response modulation (influencing physiological, experiential, or behavioral responses). The process model also incorporates a feedback loop, acknowledging the dynamic interplay between emotional responses and the eliciting situation. These processes exist on a continuum from implicit to explicit, with increasing awareness contributing to more deliberate regulation.

While valuable, the process model primarily focuses on strategy implementation success (or failure). Adaptive emotion regulation, however, requires a broader skillset, including flexible strategy selection (Bonanno & Burton, 2013). This limitation led to the "extended process model" (Gross, 2014; Sheppes et al., 2015; see Figure 1b), proposing three stages: (1) Identification: recognizing and deciding whether to regulate an emotional state; (2) Selection: choosing an appropriate regulatory strategy; and (3) Implementation: executing the chosen strategy. Each stage involves perceiving the situation, evaluating its valence, and taking action based on this evaluation.

This model raises several questions about adolescent development. Does the perception-valuation-action cycle unfold similarly across age groups? For example, given the heightened salience of social rewards (Blakemore & Mills, 2014), do adolescents perceive the need to regulate positive emotions in social contexts? Immaturities at the Selection stage are also plausible. Adolescents may have limited access to the full repertoire of regulatory strategies available to adults due to lack of awareness, practice, or the required executive function and social cognitive skills (Hofmann et al., 2012; Gross, 2014). This limitation could lead to less effective strategy selection and implementation.

Executive function and social cognition further influence strategy implementation. For instance, reappraisal, a commonly studied strategy, relies on working memory, verbal fluency, and perspective-taking (Hofmann et al., 2012; Gross, 2014). However, perspective-taking undergoes protracted development, both behaviorally (e.g., Dumontheil et al., 2010) and neurally (e.g., Pfeifer & Blakemore, 2012).

The following sections review evidence for the ongoing development of emotion regulatory processes and their neural underpinnings during adolescence, including the contributions of executive function and social cognition. Although research predominantly focuses on strategy implementation, we highlight aspects related to Identification and Selection when possible. Despite the common distinction between implicit and explicit processes, this categorization may be overly simplistic. As proposed by Gyurak et al. (2011), implicit regulation may arise from the habitual use of explicit strategies.

4. Unconciously Emotion Management

Implicit emotion regulation encompasses processes that operate without conscious awareness or deliberate intention, aiming to modulate the quality, intensity, or duration of emotional responses (Koole & Rothermund, 2011). While this definition includes the automatic use of explicit strategies, our focus remains on regulatory processes occurring in the early stages of emotion perception and processing, even in the absence of subjective emotional experience.

Emotional stimuli, particularly negative or threatening ones, capture attention (Carretié, 2014), activating limbic regions like the amygdala, which triggers an orienting response (Gamer & Büchel, 2009). While adaptive in some contexts (e.g., threat detection), exaggerated attentional capture by negative stimuli characterizes disorders like anxiety and depression (Eysenck & Derakshan, 2011; Williams et al., 1996). However, emotional stimuli are often irrelevant and can interfere with goal-directed behavior. To mitigate this, prefrontal circuits are automatically recruited to downregulate limbic responses, particularly when emotional stimuli conflict with ongoing executive tasks. A meta-analysis highlighted the involvement of the ACC, inferior frontal junction, dlPFC, and posterior medial OFC in mediating interactions between emotional stimuli and cognitive control (Cromheeke & Mueller, 2014).

Executive functions, crucial for goal representation, outcome anticipation, and response planning and execution, are frequently recruited during emotion regulation (Zelazo & Cunningham, 2007). Adult studies demonstrate the association between executive functions, such as verbal fluency, and emotion regulation abilities (Gyurak et al., 2009, 2012). Lantrip et al. (2015) found a similar pattern in adolescents, where better executive function predicted greater reappraisal use, while suppression was linked to poorer executive function. This interconnectedness highlights the shared cognitive resources underlying cognitive and emotional regulation.

Consequently, executive function tasks have been adapted to assess emotion regulation. The go/no-go task, measuring inhibitory control, requires participants to respond to frequent "go" stimuli while withholding responses to infrequent "no-go" stimuli. Emotional go/no-go variants employ emotional stimuli (e.g., faces), with poorer emotion regulation reflected in slower reaction times or increased false alarms on emotionally salient trials.

Similarly, the emotional Stroop task, an adaptation of the classic Stroop test (Stroop, 1935), measures attentional bias and interference. Participants name the ink color of emotional and neutral words, with slower responses to emotionally salient words indicating greater interference (Williams et al., 1996).

Functional neuroimaging studies utilizing these tasks (Table 1) provide insights into the neural substrates and developmental trajectory of implicit emotion regulation during adolescence.

For instance, Hare et al. (2008) found that children (7-12 years) and adolescents (13-18 years) were slower than adults in responding to fearful "go" faces in an emotional go/no-go task, suggesting greater susceptibility to affective interference. This behavioral difference was accompanied by exaggerated amygdala activity in adolescents, supporting the developmental mismatch model.

Tottenham et al. (2011), using a similar paradigm with participants aged 5-28 years, observed improvements in both emotion regulation and cognitive control with age. Crucially, the performance gap between the two narrowed with age, indicating that adults are more adept at inhibiting responses in emotionally evocative contexts.

Examining the influence of reward-related stimuli, Somerville et al. (2011) found that adolescents (13-17 years) displayed a disproportionate increase in false alarms to "happy" no-go trials compared to children (6-12 years) and adults (18-29 years). This adolescent-specific dip in performance coincided with heightened VS activity, suggesting an increased sensitivity to reward cues. Conversely, IFG activity, implicated in inhibitory control, decreased with age.

These studies highlight the dynamic interplay between limbic and prefrontal regions during implicit emotion regulation. Adolescents, characterized by heightened emotional reactivity and an underdeveloped prefrontal cortex, may rely more heavily on subcortical signaling when regulating behavior, particularly in emotionally charged contexts.

However, it's crucial to acknowledge the complexities of this developmental process. Cohen Kadosh et al. (2014), using an emotional Overlap task, found that early adolescents (11-12 years) were disproportionately slowed by fearful faces compared to late adolescents (17-18 years) on "go" trials, suggesting age-related improvements in attentional control. This finding underscores the importance of considering the specific demands of different tasks and the potential for non-linear developmental trajectories.

Further complicating the picture, Cohen-Gilbert and Thomas (2013) reported that task-irrelevant negative images disrupted inhibitory control specifically in mid-adolescents (13-14 years). This suggests that even emotionally irrelevant stimuli can impact cognitive control during this period, potentially reflecting the ongoing maturation of prefrontal regions.

Examining the neural correlates of emotion regulation in response to frustration, Perlman and Pelphrey (2011) employed an emotional go/no-go task with a frustration-inducing component. They observed distinct patterns of ACC and amygdala activation in children (5-11 years) and adults, with increasing age and frustration levels associated with stronger ACC-amygdala connectivity in children. Similarly, Lewis et al. (2006) found that adolescents, but not children, exhibited an enhanced N2 component (associated with inhibitory control) following negative emotion induction. These findings suggest developmental shifts in the neural mechanisms underlying emotion regulation, with increasing reliance on prefrontal-limbic circuitry.

Social contexts add another layer of complexity. Sebastian et al. (2010b), using a rejection-themed emotional Stroop task, reported attenuated right vlPFC responses in mid-adolescents (14-16 years) compared to adults when processing rejection-related words. This finding points to the ongoing maturation of prefrontal regions implicated in regulating social emotional responses. Similarly, Veroude et al. (2013) found that adults exhibited greater activation than late adolescents (18-19 years) in dorsomedial PFC and precuneus when processing negative stimuli, highlighting continued neural refinement into early adulthood.

These studies collectively provide compelling evidence for the protracted development of implicit emotion regulation from childhood through adolescence and into adulthood. While general improvements in attenuating emotional interference are observed, the developmental trajectory is not always linear, highlighting the importance of considering task-specific demands and individual differences. Neuroimaging studies support the role of developmental mismatches between limbic and prefrontal regions, with adolescents potentially relying more heavily on subcortical signaling in emotionally evocative contexts.

5. Consciously Managing Emotions

Explicit emotion regulation strategies require conscious effort during initiation and monitoring during implementation (Gyurak et al., 2011). Reappraisal (cognitive reframing) and suppression (inhibiting emotional expression), the most extensively studied strategies, have garnered significant attention in adolescent research. Lantrip et al. (2015) reported an association between reappraisal use and better executive function in adolescents (12-18 years) but found no age-related differences in strategy use. However, a larger longitudinal study by Gullone et al. (2010) with 1,128 adolescents revealed a decline in suppression use between 9 and 15 years of age. This decline aligns with the notion that suppression, considered maladaptive due to its association with negative mood regulation difficulties (Gross & John, 2003), diminishes as individuals develop alternative strategies (John & Gross, 2004).

Conversely, evidence regarding reappraisal development is mixed. While Gullone et al. (2010) reported a decrease in self-reported reappraisal use between 9 and 15 years of age, laboratory-based studies suggest improvements in successful reappraisal implementation (Silvers et al., 2012). Silvers et al. (2012), using a reappraisal task with participants aged 10-23 years, found that age predicted successful reappraisal, measured as the reduction in self-reported negative affect. Methodological differences between these studies, including age ranges, sample sizes, and reappraisal operationalization, may contribute to the inconsistent findings. Future research should address these discrepancies by combining self-report and experimental measures across the adolescent age range to gain a more comprehensive understanding of reappraisal development.

Neuroimaging studies are beginning to unravel the neural substrates of explicit emotion regulation during adolescence, focusing on both spontaneous and instructed regulation. McRae et al. (2012), using a reappraisal task similar to Silvers et al. (2012), reported a linear increase in reappraisal ability with age, paralleled by increased left vlPFC activation. This region, implicated in cognitive control in both emotional and non-emotional contexts, is also associated with reappraisal in adults (Ochsner & Gross, 2005, 2008). Interestingly, during unregulated emotional responding, adolescents (14-17 years) exhibited less activation in social cognitive regions (medial prefrontal cortex, posterior cingulate, temporal regions) than children (10-13 years) and emerging adults (18-22 years). However, these regions were more active during instructed reappraisal in adolescents, suggesting that while they may not automatically engage these processes, they can recruit them when explicitly instructed. However, caution is warranted in interpreting these findings, as the study did not directly assess the specific cognitive processes underlying these activations.

Further exploring reappraisal development, recent studies have examined its role in regulating food cravings, particularly for unhealthy foods (Silvers et al., 2014; Giuliani & Pfeifer, 2015). Giuliani and Pfeifer (2015), asking female participants aged 10-23 years to reappraise food cravings, found that while reappraisal success did not vary with age, right IFG activation increased with age. This suggests that older participants may have exerted greater effort to regulate their cravings.

Given the links between brain maturation and emotion regulation, investigating the relationship between structural brain development and regulatory strategy development is crucial. Vijayakumar et al. (2014) conducted a longitudinal study where participants underwent structural scans at ages 12 and 16 and reported their reappraisal and suppression use at age 19. Greater cortical thinning in left dlPFC and vlPFC, reflecting maturation, predicted greater reappraisal use at age 19, but only in females. While the underlying reasons for this sex difference remain unclear, the study highlights the potential influence of sex-specific developmental trajectories on emotion regulation.

Despite the increasing focus on explicit emotion regulation, research predominantly centers around reappraisal and suppression, neglecting the broader repertoire of strategies employed in everyday life (Aldao & Nolen-Hoeksema, 2013). Experience sampling studies in adults (e.g., Heiy & Cheavens, 2014) have identified a diverse array of strategies used to regulate both negative and positive emotional states (Table 2), highlighting the need to expand research beyond these two commonly studied strategies.

Experience sampling methods have also been used to investigate emotion regulation in adolescents. For instance, Silk et al. (2003) found that adolescents who reported using disengagement (e.g., denial, avoidance) or rumination strategies to regulate their emotions were more likely to experience depressive symptoms and externalizing behaviors. This highlights the potential of ecologically valid approaches to shed light on emotion regulation in real-world settings.

Integrating these ecologically valid methods with neuroimaging techniques holds promise for understanding the complexities of adolescent emotion regulation. Several studies have taken initial steps in this direction, linking laboratory-based neural responses to real-world emotion regulation and dysregulation in the context of psychopathology. As discussed previously, adolescence is characterized by heightened emotional reactivity, and the developmental trajectory of certain brain regions may render adolescents more susceptible to internalizing and externalizing problems. The following section examines examples from the depression (internalizing) and conduct disorder (externalizing) literature.

6. Understanding Emotions, the Brain, and Mental Health

6.1. Internalizing Symptoms

Internalizing symptoms, particularly depressive symptoms, increase dramatically during adolescence (Lee et al., 2014; Paus et al., 2008). The prevalence of major depressive symptoms rises from approximately 2% in early adolescence (13–15 years) to 15% in middle adolescence (15–18 years; Hankin et al., 1998). Adolescents with internalizing problems tend to rely on maladaptive strategies like self-blame and rumination while exhibiting lower reappraisal use (e.g., Garnefski et al., 2005).

Neuroimaging studies are beginning to elucidate the mechanisms underlying emotion regulation difficulties in adolescent depression. Studies in depressed adults implicate reduced dlPFC activity and PFC-amygdala coupling during reappraisal (e.g., Erk et al., 2010), aligning with findings that successful reappraisal relies on prefrontal regions (dlPFC, dACC, vlPFC) downregulating limbic responses (amygdala, VS, insula; Ochsner et al., 2012). However, studies in depressed adolescents suggest a different pattern. Perlman et al. (2012), comparing depressed and healthy adolescents (13–17 years) during a reappraisal task, found increased amygdala activation and decreased PFC-amygdala connectivity in the depressed group during emotion maintenance, but not during emotion reduction. This suggests that PFC-limbic dysregulation may be context-dependent in adolescent depression, potentially reflecting an ability to compensate when explicitly instructed to regulate.

This context-dependent pattern is echoed in a study employing a "chatroom" task simulating social rejection (Guyer et al., 2009). Platt et al. (2015) found that while both depressed and non-depressed adolescents (15–17 years) successfully implemented reappraisal to reduce negative affect following rejection, the depressed group exhibited increased connectivity between the right frontal pole and limbic regions (amygdala, hippocampus) specifically during reappraisal. These studies suggest that the neural mechanisms underlying emotion regulation difficulties in adolescent depression may differ from those observed in adults. However, direct cross-sectional comparisons are needed to confirm this.

Studies examining neural responses to peer rejection in typically developing adolescents (Guyer et al., 2009; Masten et al., 2009; Sebastian et al., 2011) offer further insights. Masten et al. (2011), using the Cyberball paradigm (Williams et al., 2000) to induce social rejection, found that subgenual ACC activity during rejection predicted depressive symptoms one year later. This region has been implicated in both depressive symptoms (Saxena et al., 2003) and heightened responses to peer rejection in adolescents (Masten et al., 2009). Future research could explore whether reappraisal training can modulate subgenual ACC activity in adolescents vulnerable to depression.

6.2. Externalizing Symptoms

While conduct disorder can emerge in childhood, externalizing symptoms, including aggression, theft, and property destruction, predominantly surface during adolescence (Moffitt, 1993). Aggression can be categorized as reactive (provoked, impulsive) or proactive (instrumental, goal-directed): Reactive aggression is associated with poor executive function (Giancola et al., 1996) and impulsivity (Raine et al., 2006), while proactive aggression is linked to psychopathic traits (Patrick, 2001) and callous-unemotional traits (Frick et al., 2003). While both types are moderately correlated, poor emotion regulation is more strongly associated with reactive aggression (Eisenberg et al., 2010).

Neuroimaging studies investigating conduct problems are beginning to emerge. Viding et al. (2012) found that adolescents with conduct problems and low callous-unemotional traits (reactive-aggressive subtype) exhibited amygdala hyperactivity to implicitly presented fearful faces, suggesting an exaggerated orienting response to threat cues. This hypervigilance, a hallmark of several disorders (Richards et al., 2014; Dalgleish et al., 2001), may contribute to poorly regulated behavior in this population.

Sebastian et al. (2014), studying a similar population using an implicit emotion regulation task, found that adolescents with reactive-aggressive conduct problems were disproportionately slowed when making perceptual judgments in the presence of fearful eye cues, a finding associated with increased left amygdala activation. This group also showed heightened activation in subgenual ACC and OFC, regions involved in attention to affective stimuli and integrating emotion and cognitive control, respectively (Zikopoulos & Barbas, 2012; Pessoa, 2008). These findings suggest that emotional stimuli may disproportionately interfere with executive function in adolescents with reactive-aggressive conduct problems, potentially reflecting ineffective prefrontal-limbic control.

If prefrontal-limbic dysregulation contributes to reactive aggression, then symptom improvement should coincide with improved cortical function. Lewis et al. (2008), using a frustration-inducing go/no-go task and ERP, found that children with externalizing and internalizing symptoms who showed behavioral improvements after a 14-week intervention also exhibited normalization of their N2 (inhibitory control) response. This normalization, characterized by a reduction in N2 amplitude, suggests a shift from a threat-focused regulatory style to a more adaptive response. While preliminary, this study highlights the potential of interventions to positively influence neural mechanisms underlying emotion regulation.

7. Conclusions

Recent years have witnessed a surge in research on emotion regulation development during adolescence, driven by advancements in our understanding of the neural circuitry involved. This review integrates models of adolescent brain development with models of emotion regulation, highlighting the ongoing development of processes underlying Identification, Selection, and Implementation stages.

While most research has focused on Implementation, emerging evidence suggests that both behavioral and neural responses during implicit emotion regulation tasks follow non-linear trajectories, with mid-adolescents often displaying exaggerated responses compared to younger and older individuals. This supports the notion that brain development influences behavior during this period. However, it's crucial to acknowledge that these links are complex and not always straightforward (Pfeifer & Allen, 2012).

Regarding explicit strategies like reappraisal, findings are mixed, with some studies indicating increased use with age and others reporting a decline. Methodological variations across studies make it challenging to draw firm conclusions. Future research should address these discrepancies and incorporate more ecologically valid measures to capture the complexities of real-world emotion regulation.

Key research questions remain unanswered, including:

Outstanding Questions

• What is the developmental trajectory of spontaneous versus instructed emotion regulation strategy use in adolescence?

• What are the neural correlates of the Identification and Selection stages of the extended process model in adolescents?

• Can neuroimaging biomarkers predict the development of emotion regulation difficulties or psychopathology during adolescence?

• Can interventions targeting specific neural circuits implicated in emotion regulation mitigate risk or improve outcomes for adolescents with internalizing or externalizing problems?

Link to Article

1. Introduction

Emotion regulation is a broad term that refers to how we manage our emotional reactions to achieve our goals (Thompson, 1994). It encompasses two main types: implicit and explicit emotion regulation. Implicit emotion regulation happens automatically, often outside of our conscious awareness, at the very beginning stages of processing an emotion. Explicit emotion regulation involves consciously using strategies to change our emotional responses (Gyurak et al., 2011).

Effective emotion regulation requires several skills: recognizing the emotional importance of what we perceive, understanding when regulation is needed, and choosing and using the right strategy for the situation (Sheppes et al., 2015). This means our brains have to coordinate complex processes like executive functions (Kesek et al., 2009) and social skills like understanding other people's perspectives.

Adolescence (roughly ages 10-19; Sawyer et al., 2012) is a key period for understanding emotion regulation. Adolescents face major biological and social changes, a growing need for independence, and pressures from school and relationships (Casey et al., 2010). These challenges often lead to increased emotional reactivity and stress. Some researchers believe that adolescent brains, still under development, are not as equipped to regulate emotions, making them more vulnerable to anxiety and stress-related disorders (Powers and Casey, 2015). Notably, adolescence is marked by a rise in internalizing and externalizing symptoms, suggesting a potential vulnerability to emotional dysregulation (Lee et al., 2014; Paus et al., 2008; Spear, 2000).

The teenage years are also when higher-level thinking and social skills essential for emotion regulation—like working memory, impulse control, abstract reasoning, decision-making, and perspective-taking—are still developing (Blakemore & Robbins, 2012; Dumontheil, 2014; Sebastian et al., 2010a; Somerville & Casey, 2010). These cognitive developments are linked to physical changes in the brain, particularly in the prefrontal cortex and its connections with emotion centers (see below). At the same time, teenagers are navigating increasingly complex social situations (Sebastian et al., 2010a; Vartanian, 2000).

The interaction of these brain changes and social pressures could explain why emotional development in adolescence isn't always linear. This might contribute to the emotional ups and downs and risk-taking behaviors often seen in teenagers (Casey & Caudle, 2013). Therefore, adolescence might be a crucial period for developing healthy emotion regulation, impacting long-term emotional well-being and mental health. Because adolescence is a time of significant learning and adaptability (Casey et al., 2008; Steinberg, 2005), it's a prime window for interventions that could have long-lasting positive effects on mental health (Wekerle et al., 2007).

This review will explore the growing body of behavioral and brain imaging research on implicit and explicit emotion regulation in adolescents, highlighting promising areas for future research. We'll begin with a brief overview of how brain structures involved in emotion detection, expression, and regulation change during adolescence (see Blakemore, 2012; Giedd, 2008; Giedd & Rapoport, 2010; Lenroot & Giedd, 2006; Paus, 2005, for detailed reviews of adolescent brain development). Next, we'll delve into behavioral and neuroimaging data from humans, investigating the development of emotion regulation from automatic, implicit control (like filtering out emotional distractions) to conscious, effortful strategies. This section will generally follow the Process Model of Emotion Regulation (Gross, 1998) and the more recent Extended Process Model (Sheppes et al., 2015). fMRI research suggests that although conceptually distinct, implicit and explicit processes might share some neural mechanisms (Drabant et al., 2009). Due to existing comprehensive reviews (Blakemore & Robbins, 2012; Casey & Caudle, 2013; Steinberg, 2008), we won't cover risky decision-making, although emotion regulation undoubtedly plays a role.

2. Adolescent Brain Development and Emotion Regulation

Adolescence is a period of heightened emotional reactivity, characterized by fluctuating emotions and increased risk-taking. Studies using questionnaires show that compared to adults and children, teenagers are more sensitive to peer rejection and influence (Kloep, 1999; Larson & Richards, 1994; O’Brien & Bierman, 1988). A longitudinal study found that, on average, emotional states become more negative during early adolescence but stabilize by late adolescence (around 18 years old) (Larson et al., 2002). This suggests that emotional experiences become steadier with age.

Behavioral studies have also demonstrated this heightened emotional reactivity. For instance, in experiments manipulating social exclusion, adolescents reported significantly lower moods and higher anxiety after being excluded compared to adults, who showed no difference in mood or anxiety (Sebastian et al., 2010a). Adolescents also seem to place a higher value on rewards, especially social ones, which might explain why they sometimes perceive benefits as outweighing risks (Reyna & Farley, 2006; Steinberg, 2008).

In recent decades, neuroimaging studies have started to provide evidence that ongoing brain development during adolescence could contribute to these adolescent-specific behaviors. Research suggests that brain regions involved in emotion regulation, particularly the prefrontal cortex (PFC), continue to develop into adulthood (Paus et al., 2008). The PFC is crucial for creating and maintaining emotion regulation strategies (Ochsner & Gross, 2008; see Box 1). Key PFC areas for emotion processing and regulation include the dorsolateral PFC (dlPFC), ventrolateral PFC (vlPFC), and ventromedial PFC (vmPFC) (Kalisch, 2009; Ochsner & Gross, 2008).

The PFC follows a prolonged developmental trajectory, with gray matter volume, density, and thickness continuing to decrease throughout adolescence and even into the third decade of life (Gogtay et al., 2004; Shaw et al., 2008). These decreases are thought to reflect brain maturation, possibly due to synaptic pruning—the elimination of unnecessary connections between brain cells (Blakemore, 2008). Post-mortem studies have shown that the density of synapses (connections between neurons) increases throughout childhood, peaks in early adolescence, and then drops by about 40% during adolescence and early adulthood before stabilizing (Huttenlocher & de Courten, 1987). This pruning process refines brain networks, potentially leading to more efficient information processing (Blakemore, 2008).

However, some scientists argue that the decrease in synapse numbers during adolescence is unlikely to be the sole reason for the significant decrease in gray matter volume observed in MRI scans. Gray matter contains various cell types, including neurons, glial cells, and blood vessels. Therefore, the observed gray matter decline might be an artifact of increased myelination—the process of coating nerve fibers with myelin, a fatty substance that speeds up signal transmission (Bourgeois & Rakic, 1993; Paus, 2005; Paus et al., 2008). Due to methodological limitations, directly linking these structural brain changes observed in MRI with changes at the cellular level remains challenging.

Subcortical and limbic regions, deeply involved in generating and regulating emotions, also undergo developmental changes during adolescence. For example, the amygdala, which plays a crucial role in processing emotions, particularly fear, increases in volume between the ages of 7.5 and 18.5 years (Schumann et al., 2004). The amygdala has extensive connections with regulatory regions, including the medial and lateral orbitofrontal cortices, anterior cingulate cortex (ACC), and dlPFC (Bracht et al., 2009; Johansen-Berg et al., 2008). These connections continue to mature during adolescence, leading to enhanced top-down control and strengthening frequently used pathways (Gee et al., 2013). This enhanced connectivity results from a steady increase in white matter volume and density, although this slows down in adulthood (Giedd et al., 1999; Ostby et al., 2009; Tamnes et al., 2013). This increase in white matter likely reflects ongoing myelination, improving communication efficiency between brain regions (see Perrin et al., 2009 for a discussion on sex differences in white matter maturation).

These structural findings demonstrate that brain regions responsible for generating and regulating emotions continue to develop throughout adolescence and beyond. Adolescence, therefore, presents a window of opportunity for these circuits to be shaped by experience. It is also clear that structural development does not always follow a linear path, with both quadratic and cubic trajectories observed (Mills et al., 2014; Shaw et al., 2008). Moreover, different brain regions develop at varying rates within the same individual, with connectivity between these regions also in flux. This uneven development is thought to have significant implications for socioemotional processing and behavior during the teenage years. However, we still have much to learn about how these well-documented structural changes in the adolescent brain translate into functional differences in brain activity and, subsequently, behavior.

Nevertheless, several models have been proposed to explain the link between adolescent brain development and behavior. For instance, some researchers suggest a "developmental mismatch" or "imbalance" between brain systems responsible for emotional reactivity and those responsible for regulation. According to this theory, the development of prefrontal regions, crucial for control and regulation, lags behind the development of limbic structures like the amygdala, ventral striatum (VS), and orbitofrontal cortex (OFC), which are involved in emotional responses (Casey et al., 2008; Somerville & Casey, 2010; Steinberg, 2008). As a result, during this period of lagging prefrontal development, adolescents may be less effective at regulating their emotions and more susceptible to emotional influences (like peer pressure) when making decisions.

More recently, the "Triadic Systems Model" (Ernst, 2014) proposes an imbalance between three key systems: the PFC (regulatory control), striatum (approach behaviors), and amygdala (avoidance). Unlike the dual-system models, it highlights the importance of both approaching rewarding situations and avoiding threatening ones. It suggests that these three systems mature at different paces, and this asynchronous development, coupled with less mature connections between brain regions, might contribute to adolescent risk-taking.

Although these models provide valuable insights, they have also faced criticism for oversimplifying the relationship between brain development and behavior (Pfeifer & Allen, 2012). Contrary to these models, not all studies have consistently found heightened amygdala responses to emotional stimuli during adolescence (McRae et al., 2012; Pfeifer et al., 2011; Vasa et al., 2011). Additionally, increased VS responses have been linked to positive outcomes like reduced risky behavior, increased resistance to peer influence, and fewer negative feelings after social exclusion (Pfeifer et al., 2011; Masten et al., 2009). Conversely, diminished VS activity (and increased prefrontal activity) in response to reward anticipation and outcomes has been associated with lower self-reported positive emotions and higher levels of depression in typically developing adolescents (Forbes et al., 2010). Therefore, it's crucial to consider the complexity of these interactions rather than attributing adolescent behavior solely to an immature PFC.

To better understand the complexities of adolescent emotional development, researchers have started to integrate hormonal factors into these models. For example, Crone and Dahl (2012) suggest that hormonal changes during puberty influence the limbic system, contributing to shifts in social and emotional responses. These social and emotional influences interact with developing cognitive control systems, leading to greater flexibility in how adolescents engage their frontal lobes depending on the situation. While this interplay is usually adaptive and helpful for learning, certain situations—perhaps due to individual vulnerabilities or risky environments—can lead to negative consequences like substance abuse or depression.

Typically, in cognitive neuroscience, a cognitive function is first thoroughly investigated through behavioral experiments. Then, neuroscientific techniques like brain imaging are employed to examine the neural underpinnings of these functions, refining our understanding of how the brain supports these processes. However, research on adolescent emotion regulation has taken a slightly different path. Discoveries about the ongoing and uneven brain development during adolescence sparked renewed interest in how the functions supported by these brain regions evolve. While functional neuroimaging studies have examined specific aspects of emotion regulation in adolescents, surprisingly, behavioral studies on this topic have been relatively scarce until recently (Adrian et al., 2011). Fortunately, this is changing, with neuroimaging findings providing a valuable context for behavioral investigations. Additionally, adolescent emotion regulation research is beginning to benefit from the extensive theoretical and practical knowledge gained from decades of research on adult emotion regulation.

In the next section, we'll discuss influential models of adult emotion regulation, providing a framework for understanding how emotion regulation develops during the teenage years.

3. Models of Emotion Management

There are numerous strategies for regulating emotional responses. One prominent approach to understanding these strategies focuses on the timing of their deployment in response to emotionally charged situations. The "Process Model" of Emotion Regulation proposes that emotions and their regulation unfold in a specific sequence (Gross, 1998, 2014). The first two processes, situation selection and situation modification, involve shaping the situation itself. Emotionally charged situations trigger early emotional reactivity—an immediate, often intense, and involuntary reaction accompanied by responses like attentional bias and physiological changes. This early reactivity is largely implicit, occurring before conscious awareness. As awareness increases, individuals can actively choose which situations to engage in (situation selection) and modify their emotional impact (e.g., by limiting exposure time; situation modification). Situation selection is frequently observed in mental health conditions like social anxiety disorder, where individuals avoid social situations to manage their anxiety (Wells & Papageorgiou, 1998).

Attentional deployment is the next step, directing focus away from aspects of the situation that trigger unwanted emotions. Once an emotional situation is recognized, individuals engage in cognitive change. This can involve reappraisal—reinterpreting the situation's meaning to lessen its negative impact—or response modulation—directly influencing physiological, experiential, or behavioral emotional responses after they've been triggered. For example, exercise and relaxation techniques can be used to diminish the physiological and experiential effects of negative emotions (Oaten & Cheng, 2006). A well-studied form of response modulation is expressive suppression, which involves inhibiting outward emotional expressions (Gross, 2002).

The Process Model also includes a feedback loop, acknowledging that emotional responses can change the situation that triggered them, suggesting a dynamic and ongoing cycle of emotion generation (Gross & Thompson, 2007). The processes in this model can be visualized on a spectrum from implicit to explicit regulation: as we become more aware of our emotional reactions, our regulation becomes more conscious and deliberate. However, pinpointing the exact moment when regulation transitions from implicit to explicit is challenging, as it likely varies between individuals and situations.

However, while the Process Model focuses primarily on the success or failure of implementing specific strategies, adaptive emotion regulation involves a broader set of skills, including choosing the right strategy for the situation (Bonanno & Burton, 2013). This recognition led to the development of the "Extended Process Model" (Gross, 2014; Sheppes et al., 2015; see Figure 1b).

This model proposes that emotion regulation occurs in three stages:

1. Identification: Recognizing an emotional state and deciding whether or not to regulate it.

2. Selection: Choosing an appropriate regulation strategy.

3. Implementation: Putting the chosen strategy into action (corresponding to the original Process Model).

Each stage involves three steps: 1) Perception: becoming aware of the situation, 2) Valuation: judging whether the situation is good or bad, and 3) Action: responding based on that judgment.

For example, during Identification, you might perceive a feeling of sadness, evaluate it as exceeding your tolerance, and decide you need to regulate it. This then leads to the Selection stage, where you consider and evaluate potential regulation strategies and choose the most appropriate one. Finally, during Implementation, you put the selected strategy into action.

When we consider models of adolescent brain development alongside the Extended Process Model, several questions arise. Does the perception-valuation-action cycle unfold similarly in adolescents compared to adults at each stage? For instance, considering the importance of social rewards during adolescence (Blakemore & Mills, 2014), could it be that positive emotions experienced with peers don't trigger the need to regulate during the Identification stage? Conversely, adolescents might face challenges during the Selection stage. While a wide array of regulatory strategies exists, adolescents might not have access to the same range as adults. This could be because they are unaware of certain strategies, haven't had enough practice using them, or because some strategies require advanced executive functions (Hofmann et al., 2012) or social cognition skills (Gross, 2014), which are still developing during adolescence. If these skills are not fully developed, adolescents might struggle to select from the same range of strategies as adults or choose strategies they cannot effectively implement. Developing executive function skills might also impact the ability to flexibly switch between strategies during Selection if the initial strategy proves ineffective.

Executive functions and social cognitive skills likely play crucial roles in the Implementation stage as well. For instance, reappraisal (cognitively reframing a situation) requires executive functions like working memory and verbal fluency (Hofmann et al., 2012). Furthermore, it requires the ability to take another person's perspective (Gross, 2014). For example, if a teacher is short with a student, a typical reappraisal response would be to consider that the teacher might be having a bad day. However, research shows that the ability to take another's perspective undergoes significant development throughout adolescence, both behaviorally (Dumontheil et al., 2010) and neurally (Pfeifer & Blakemore, 2012).

The following sections will delve into the evidence for the continuous development of emotion regulation processes and their neural bases during adolescence. We will also discuss the role of executive functions and social skills in these processes. To date, research has primarily focused on the Implementation stage, providing participants with a strategy and measuring its effectiveness. However, we will touch upon Identification and Selection whenever possible.

These sections will broadly distinguish between implicit and explicit processes, recognizing that this distinction might be overly simplistic, and the lines between them are likely blurred. For example, Gyurak et al. (2011) proposed that implicit emotion regulation might emerge from the habitual use of specific explicit strategies. For instance, consciously reminding oneself that an angry coworker had a bad day might, over time, lead to the same regulation process occurring automatically, without conscious effort.

4. Implicit Management of Emotions

Implicit emotion regulation is defined as "any process that operates without the need for conscious supervision or explicit intentions, and aims at modifying the quality, intensity, or duration of an emotional response" (Koole & Rothermund, 2011, p. 1). While this definition encompasses the automatic and habitual use of strategies typically considered explicit, this section will focus on regulatory processes occurring at the earliest stages of emotion perception and processing. These processes happen even when we are unaware of experiencing a subjective emotional response.

Emotional stimuli grab our attention (see Carretié, 2014 for a review), activating brain regions like the amygdala, which triggers an orienting response to important stimuli (Gamer & Büchel, 2009). This can be adaptive, as such stimuli might require immediate action (e.g., avoiding danger). However, emotional stimuli in our environment are often irrelevant and can interfere with our current goals. Therefore, our brains automatically engage regulatory processes, often involving the PFC, to downregulate these limbic responses, especially when emotional stimuli could disrupt an ongoing task requiring focus and control. A recent meta-analysis of how emotional stimuli and cognitive control interact in adults highlighted the involvement of the ACC, inferior frontal junction, dlPFC, and posterior medial OFC in these processes (Cromheeke & Mueller, 2014).

It's no surprise then that executive functions are frequently recruited during emotion regulation. We need to remember our goals, anticipate outcomes, and plan and execute responses (Zelazo & Cunningham, 2007). Studies in adults have shown that stronger executive functions, like verbal fluency, are associated with a greater ability to both decrease and increase emotional responses (Gyurak et al., 2009, 2012). A recent study in adolescents found similar results. Using questionnaires, Lantrip et al. (2015) found that better executive functions were linked to greater use of reappraisal, while relying on suppression was associated with weaker executive functions, such as poorer inhibitory control, problem-solving, and organizational skills. These findings suggest a close relationship between executive functions and emotion regulation, with executive functions supporting the regulation of both cognitive and emotional processes.

Therefore, tasks designed to measure executive functions have been adapted to assess emotion regulation. The go/no-go task is frequently used to study attention and inhibitory control. In this task, participants respond by pressing a button when certain stimuli appear (Go) and withhold their response when a specific target stimulus appears (No-Go). Because Go trials are more frequent, the task measures the ability to inhibit a dominant response. When emotional stimuli are incorporated (e.g., the No-Go stimulus is emotional), the task requires more implicit emotion regulation, as emotions can interfere with the ability to inhibit the response. Slower reaction times on Go trials or more errors on No-Go trials indicate poorer emotion regulation.

Another task measuring inhibitory control and attentional bias is the Stroop test (Stroop, 1935), where participants name the ink color of a word while ignoring the word itself. Research consistently shows that it takes longer to name the color when the word is an incongruent color name (e.g., the word "RED" written in blue ink) compared to a neutral stimulus (van Maanen et al., 2009). The emotional Stroop task is an adaptation where participants name the ink color of emotional and neutral words. Emotionally charged words, especially those personally relevant, tend to capture attention more than neutral words, leading to slower reaction times (see Williams et al., 1996 for a review). As with the go/no-go task, implicit emotion regulation here is defined as the ability to maintain cognitive control in the presence of these emotionally charged words.

Several neuroimaging studies have employed variations of these tasks (summarized in Table 1) to investigate the neural underpinnings and developmental trajectory of implicit emotion regulation in adolescents. For example, Hare et al. (2008) used a modified go/no-go task and found that children (aged 7-12) and adolescents (aged 13-18) were slower than adults when responding to fearful faces. This suggests that they were less effective at overriding the emotional interference, particularly when the response involved avoiding a potentially threatening stimulus. At the neural level, adolescents displayed greater amygdala activity compared to both children and adults across different facial expressions. However, this heightened response decreased with repeated exposure to the stimuli, indicating a non-linear developmental trajectory of amygdala response, potentially consistent with "developmental mismatch" theories.

This study was followed by several behavioral and fMRI studies examining adolescent development in more detail. Tottenham et al. (2011) used a similar go/no-go task with 100 participants aged 5-28 years. Emotion regulation performance was defined as the error rate on No-Go trials with emotional faces, reflecting the ability to inhibit responses in emotionally charged situations. General cognitive control was measured as the error rate on No-Go trials with neutral faces. Both emotion regulation and cognitive control improved with age, but importantly, the gap between the two narrowed. This means that adults showed a smaller difference in performance between inhibiting responses to emotional faces and neutral faces compared to children and adolescents.

An fMRI study using a go/no-go task with happy and neutral faces found that adolescents (13-17 years) made significantly more errors on No-Go trials with happy faces compared to both children (6-12 years) and adults (18-29 years) (Somerville et al., 2011). This adolescent-specific dip in performance was accompanied by increased activity in the VS, a brain region involved in processing and anticipating rewards (Schultz, 2006). Conversely, activity in the inferior frontal gyrus (IFG), typically activated during inhibitory control (Aron et al., 2004), decreased with age for No-Go trials relative to Go trials and was positively correlated with overall errors on No-Go trials. Connectivity analyses between the IFG and striatum also revealed age-related differences. Children exhibited reduced functional coactivation between these regions on happy No-Go trials compared to happy Go trials, unlike adolescents and adults. Adolescents, on the other hand, showed increased coactivation between the dlPFC and VS compared to both children and adults. These neural patterns during adolescence seem to support the models discussed earlier: when needing to regulate their behavior, adolescents might be disproportionately driven by signals from subcortical regions like the VS, which shows this inverted U-shaped developmental trajectory, while their prefrontal regulatory systems are still maturing.

In these studies, the emotional content of the stimuli was directly relevant to task performance. Participants had to distinguish between emotional and neutral faces to make the go/no-go decision, even if they didn't have to explicitly identify the specific emotion. However, the ability to recognize facial expressions continues to develop throughout adolescence, with different expressions developing at different rates (Durand et al., 2007; Thomas et al., 2007). This factor could partially explain the developmental differences observed in these go/no-go tasks or introduce unexpected variability in the results.

To address this, recent studies have explored inhibitory control in the context of task-irrelevant emotional information. Cohen Kadosh et al. (2014) used a modified emotional go/no-go task called the Overlap task (Bindemann et al., 2005) to compare younger (11-12 years) and older (17-18 years) adolescents. They found that younger adolescents were disproportionately slower on Go trials with fearful faces compared to happy or neutral faces. This suggests that younger adolescents might have weaker attentional control in the presence of fear-related stimuli, potentially reflecting ongoing dlPFC maturation. It's possible that fearful faces captured their attention more readily, or they had more difficulty disengaging their attention once it was captured. Interestingly, unlike the previous emotional go/no-go tasks, this study found no age differences in accuracy for either Go or No-Go trials, suggesting that developmental differences in inhibitory control during adolescence might be less pronounced when emotional information is not directly relevant to the task. This interpretation is supported by a study by Schel and Crone (2013), who directly compared go/no-go task versions with task-relevant and task-irrelevant emotional stimuli in participants aged 6-25 years. They found that only task-relevant emotion significantly influenced inhibition.

However, it's also possible that the development of inhibitory control in emotionally charged situations during adolescence follows a subtler, non-linear trajectory, requiring larger samples and a wider age range to be detected. This approach was taken by Cohen-Gilbert and Thomas (2013) in a study with 100 participants. They used a go/no-go task where participants responded to letters presented on backgrounds of negative, positive, neutral, or scrambled images. While all age groups were slower on trials with negative backgrounds, lower accuracy on No-Go trials with negative images was specifically observed in adolescents aged 13-14 years. This suggests that negative emotional input might disrupt regulatory efforts more easily during early to mid-adolescence, even when the emotional information isn't directly relevant to the task. However, this study used less controlled visual stimuli (pictures and scenes) compared to facial expressions, which could have influenced the results. Nevertheless, the age-related patterns observed in emotion-related inhibitory control in this study align with the findings from emotional go/no-go tasks where emotion is task-relevant. Further research is needed to understand why task-irrelevant emotion affected inhibitory control in this study but not others. One possibility is that negative images are more emotionally arousing than negative facial expressions, or that the use of finer-grained age distinctions in this study allowed for the detection of subtler developmental differences.

Another approach to studying inhibitory control in the context of emotion is to directly elicit emotional states in participants. Perlman and Pelphrey (2011) conducted a developmental fMRI study where children (5-11 years) and adults performed a go/no-go task while gaining and losing points towards a reward. The task was designed to induce frustration by having participants lose all their previously earned points. Children and adults showed distinct patterns of activation in the ACC and amygdala when emotion regulation was required. For instance, children showed decreased amygdala activity while recovering from frustration, while adults showed the opposite pattern. Connectivity analyses revealed that as frustration (and thus the need for regulation) increased, the functional connection between the ACC and amygdala also increased. Importantly, this connectivity became stronger with age in children, indicating that the neural maturation of this pathway might continue into early adolescence. While this study didn't specifically examine adolescent development, an ERP study by Lewis et al. (2006) using a similar task with participants aged 5-16 years found an increased N2 component (associated with inhibitory control) in adolescents but not children in response to frustration. These findings suggest that different brain regions might be involved in emotion regulation as children transition into adolescence.

During early and mid-adolescence, peer relationships become particularly salient. Individuals become increasingly sensitive to acceptance and rejection by their peers (Brown, 2004; Nelson et al., 2005; Sebastian et al., 2010a) and more aware of others' opinions (Parker et al., 2006; Vartanian, 2000). Based on this, Sebastian et al. (2010b) used a rejection-themed emotional Stroop task with fMRI and found that mid-adolescents (aged 14-16) showed reduced right vlPFC activity compared to adults when processing rejection-related words. This finding aligns with theories suggesting continued development of prefrontal regulatory regions between mid-adolescence and adulthood. While emotion was task-irrelevant and regulation implicit in this study, it's possible that this task tapped into immature prefrontal mechanisms that contribute to heightened sensitivity to rejection during adolescence, especially considering the overlap in prefrontal regions recruited during both implicit and explicit social rejection tasks.

An emotional Stroop task was also used to compare late adolescents (18-19 years) and young adults (23-25 years; Veroude et al., 2013). Adults showed greater activation in the dorsomedial PFC and precuneus than late adolescents when processing negative words. While the right vlPFC region, which differentiated age groups in the rejection-themed Stroop task, didn't show age differences in response to emotional words in this study, the left inferior frontal gyrus exhibited reduced activation in late adolescents in a non-emotional contrast. This study demonstrates that the maturation of regulatory mechanisms involved in processing emotional information continues even between late adolescence and early adulthood. This period, often referred to as "emerging adulthood," is receiving increasing attention as researchers aim to understand how the identity formation and role changes occurring during this time relate to ongoing brain development.

While most research on implicit emotion regulation has focused on inhibitory control, there's also evidence for ongoing development in how working memory and emotional processing interact. Ladouceur et al. (2009) used an emotional n-back task where participants viewed a sequence of items and indicated whether each item matched the one presented n items back, all while emotional or neutral faces were presented as distracters. In this behavioral study, they examined performance on trials with fearful and neutral faces and varying working memory loads. They found that reaction times on trials with higher working memory load and fearful distracters decreased with age, but only for participants with high trait anxiety. The role of individual differences in emotion regulation and personality traits during adolescence will be discussed further in Section 6, focusing on psychopathology.

In summary, these behavioral and neuroimaging studies shed light on specific implicit emotion regulation processes that continue to develop from childhood through adolescence and into adulthood, providing valuable insights into their developmental trajectories. Data from reaction time and accuracy measures across different tasks generally show improvements in the ability to resist emotional interference between adolescence and adulthood (Cohen Kadosh et al., 2014; Tottenham et al., 2011). However, some studies indicate a non-linear developmental path, with increased interference in mid-adolescence compared to earlier childhood (Cohen-Gilbert & Thomas, 2013).

Neuroimaging research suggests that the mechanisms underlying these effects align with developmental mismatch and triadic model accounts of adolescent brain development. Studies have reported increased limbic responses to emotional stimuli (Hare et al., 2008), reduced prefrontal control (Sebastian et al., 2010b; Veroude et al., 2013), and altered or reduced connectivity between these systems during adolescence (Somerville et al., 2011). These findings strongly suggest that the ability to effectively filter out emotional distractions and maintain focus on goals continues to mature throughout adolescence. The next section will explore whether similar evidence exists for the development of explicit emotion regulation processes.

5. Explicit Management of Emotions

Explicit emotion regulation strategies require conscious effort to initiate and some degree of monitoring during implementation (Gyurak et al., 2011). As previously discussed, cognitive reappraisal (reinterpreting emotionally evocative situations in a more positive light) and expressive suppression (masking outward displays of emotional reactions) have been the focus of most research, both in adolescents and in emotion regulation research generally. Lantrip et al. (2015) found that while reappraisal use was linked to better executive functions in adolescents (12-18 years), there were no age-related differences in strategy use. However, their sample size was relatively small (N = 70) compared to a longitudinal study by Gullone et al. (2010) involving 1128 adolescents. Gullone et al. (2010) used self-report measures and found that suppression use decreased between ages 9 and 15.

Suppression is often considered a less adaptive strategy, as it's associated with difficulty managing negative moods and experiencing positive emotions (Gross & John, 2003). Therefore, this decrease in its use during adolescence makes sense, as individuals gain experience and develop the executive functions and social skills needed for more effective strategies (John & Gross, 2004). Following this logic, we might expect the use of the more adaptive strategy, reappraisal, to increase during this period. However, the evidence so far has been mixed. Contrary to expectations, Gullone et al. (2010) observed an overall decrease in self-reported reappraisal use in everyday life between ages 9 and 15. However, lab-based studies using reappraisal tasks suggest that the ability to effectively use reappraisal, at least when instructed, might improve with age (Silvers et al., 2012).

Silvers et al. (2012) had 44 participants aged 10-23 view negative and neutral images and rate their negative feelings. Participants were either instructed to simply "look" at the image and report their natural response or to actively "decrease" their negative feelings using reappraisal techniques taught before the experiment. Reappraisal success was defined as the percentage decrease in self-reported negative affect during "decrease" trials compared to "look" trials for negative images. The study found that reappraisal success improved with age, following both linear and quadratic trends.

It's worth noting the methodological differences between these studies that might explain the inconsistent findings, such as variations in age range, sample sizes, and how reappraisal was measured (frequency vs. success). Future research should combine self-report and experimental measures of reappraisal use and success across adolescence to address these discrepancies (see Box 2 "Outstanding Questions"). While such research exists in adults, challenges remain due to varying methodologies and timeframes for measuring frequency and success. More research is needed to understand how emotion regulation success unfolds in real-world settings over extended periods, both in adults and adolescents (see McRae, 2013 for a discussion on future directions).

Neuroimaging research on explicit emotion regulation strategies in adolescents has begun to investigate age-related differences in both spontaneous and instructed regulation. McRae et al. (2012) had participants aged 10-22 complete a reappraisal task while undergoing fMRI. Similar to Silvers et al. (2012), they found a linear increase in cognitive reappraisal ability with age, accompanied by an age-related increase in left vlPFC activity. As previously mentioned, this brain region is involved in cognitive control in various contexts.

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1. Introduction

Emotion regulation is basically how we control our emotions to reach our goals. It involves noticing, checking, and changing how we react to things. We can regulate our emotions automatically without realizing it (implicit emotion regulation) or consciously use strategies to change how we feel (explicit emotion regulation). To regulate our emotions well, we need to understand the emotional meaning of things, know when we need to control our feelings, and then pick the right way to do it. This involves many complex processes in our brains, like paying attention, controlling impulses, understanding abstract ideas, making decisions, and seeing things from other people's perspectives.

Adolescence (roughly ages 10–19) is a fascinating time for understanding emotion regulation. This period brings major changes in our bodies, a desire for independence, pressure from school and maybe even jobs, and ups and downs in our social lives. These challenges often come with stronger emotional reactions and stress. Some scientists believe that the developing teenage brain struggles to regulate emotions effectively, making adolescents more vulnerable to anxiety and stress-related problems. This might be why we see more emotional difficulties during adolescence.

The teenage brain is still developing the advanced thinking and social skills needed for good emotion regulation. These skills include things like remembering information, controlling impulses, thinking abstractly, making decisions, and understanding other people's viewpoints. At the same time, teenagers face increasingly complex social situations. These social pressures combined with changes in the brain might explain why emotional development during adolescence can be unpredictable. This might also be one reason why teenagers experience more emotional ups and downs and risk-taking compared to adults and younger children. Adolescence is likely a crucial time for developing healthy emotion regulation, which can have lasting effects on mental health. Because teenage brains are flexible and adaptable, this period could be a golden opportunity for learning effective emotion regulation strategies, which could have positive and long-lasting benefits for mental well-being.

This review looks at the growing evidence from behavior and brain imaging about how implicit and explicit emotion regulation develops during adolescence and suggests exciting areas for future research. We'll start by discussing how the parts of the brain responsible for recognizing, expressing, and regulating emotions develop throughout adolescence. Then, we'll delve into studies on teenagers' behavior and brain activity that explore how various aspects of emotion regulation develop, ranging from automatic emotional control (like filtering out emotional distractions) to conscious and deliberate strategies for managing emotions. We won't be talking about risky decision-making, even though emotion regulation definitely plays a role, because other in-depth reviews already cover that.

2. Adolescent Emotion Management

Adolescence is often marked by heightened emotional sensitivity, fluctuating moods, and risk-taking behaviors. Several studies have found that, compared to adults and children, adolescents are more sensitive to peer rejection and influence. Additionally, while young people experience a dip in emotional well-being during early adolescence, this stabilizes by late adolescence (around 18 years old). This increased emotional reactivity is also evident in studies where teenagers were intentionally excluded from social interactions. These studies showed that exclusion negatively impacted the mood and increased anxiety in adolescents more than in adults. Teenagers also tend to place a higher value on rewards, especially social rewards, compared to adults, which might explain why they sometimes perceive the benefits of risky behavior as outweighing the risks.

In recent decades, brain imaging studies have provided clues about how the developing teenage brain contributes to these adolescent-specific behaviors. The prefrontal cortex (PFC) plays a crucial role in devising and maintaining emotion regulation strategies. Within the PFC, the dorsolateral (dlPFC), ventrolateral (vlPFC), and ventromedial (vmPFC) regions are particularly important for processing and regulating emotions. The PFC takes a long time to fully develop, with changes in its size, density, and thickness continuing well into adulthood.

These changes likely reflect the brain's way of fine-tuning itself. One theory is that these changes are due to synaptic pruning, where the brain removes unnecessary connections between brain cells. Studies have found that the number of connections between brain cells increases throughout childhood, peaks in early adolescence, and then decreases by roughly 40% during adolescence and early adulthood. This pruning process might be how the brain refines remaining connections, making cognitive processing more efficient. However, other researchers believe that this reduction in connections is not the main reason for the changes in the brain's size observed on MRI scans. They argue that these changes might be due to increased insulation (myelination) of the connections between brain cells, which speeds up communication within the brain. More research is needed to fully understand this.

Other areas of the brain important for emotions, like the subcortical and limbic regions, also undergo significant development during adolescence. For instance, the amygdala, which plays a crucial role in processing emotions like fear, grows in volume between the ages of 7.5 and 18.5. The amygdala has numerous connections with brain regions involved in regulation, like the prefrontal cortex (including the medial and lateral orbitofrontal cortices, the anterior cingulate cortex (ACC), and the dlPFC). These connections continue to mature throughout adolescence, resulting in better control over emotional responses. This enhanced connectivity is primarily due to a steady increase in the volume and density of white matter, the brain's wiring, during adolescence; however, this growth slows down as we enter adulthood.

The research on brain structure reveals that areas responsible for generating and regulating emotions keep developing during adolescence and beyond, suggesting that adolescence might be a period of significant adaptability for these brain circuits. Importantly, brain development doesn't always follow a straight path. Instead, different brain areas that work together for emotion processing and regulation mature at different speeds within the same individual. Some researchers believe that this uneven development might explain certain social and emotional behaviors during adolescence. However, more research is needed to understand how these structural changes in the brain actually impact brain function and behavior.

Despite these challenges, scientists have proposed various models to explain the relationship between brain development and behavior during adolescence. For example, several researchers suggest a "developmental mismatch" or "imbalance" theory. They argue that during adolescence, the prefrontal cortex, which is responsible for self-control, develops slower than areas of the brain that drive emotional reactivity, such as the amygdala, ventral striatum (VS), and orbitofrontal cortex (OFC). This lag in development might make teenagers less effective at controlling their emotions and more susceptible to emotional influences (like peer pressure) when making decisions.

Building on this idea, the "Triadic Systems Model" emphasizes the interplay between three key brain systems: the PFC (control), the striatum (approach), and the amygdala (avoidance). This model highlights the importance of both approaching rewards and avoiding threats and suggests that these systems mature at different rates. This difference in timing, along with immature connections between these brain regions, might contribute to risky behavior in adolescence.

Although these models present a compelling narrative about how immature prefrontal regions might contribute to poor emotion regulation in adolescents, some scientists have challenged this view. Some studies haven't consistently found heightened amygdala responses to emotional stimuli during adolescence. Moreover, some studies even suggest that increased activity in the VS, an area associated with reward, might be linked to positive outcomes like reduced risk-taking, better resistance to peer pressure, and fewer negative feelings after social exclusion. Conversely, decreased VS activity (and increased prefrontal activity) in response to rewards has been linked with lower levels of happiness and more depressive symptoms in typically developing teens. These findings suggest that the "developmental mismatch" models might oversimplify the relationship between brain development and behavior in teenagers.

Recognizing the role of hormones in brain development, Crone and Dahl proposed a model suggesting that hormonal changes during puberty influence the limbic system (the emotional center of the brain). This influence interacts with developing cognitive control systems in the frontal cortex, leading to flexibility in how teenagers engage these systems depending on the situation. This interplay is usually adaptive and helpful for navigating the learning demands of adolescence. However, certain situations, especially when combined with personal vulnerabilities and risky environments, can lead to negative consequences like substance abuse or depression.

Traditionally, scientists first study a cognitive function through behavioral experiments and then use neuroscientific techniques to understand its neural basis. However, research on emotion regulation in adolescents has taken a different route. Discoveries about the ongoing and uneven development of the adolescent brain have sparked renewed interest in how the functions controlled by these developing brain areas evolve. While neuroimaging studies have explored specific aspects of emotion regulation in teenagers, there haven't been enough behavioral studies on this topic until recently. Fortunately, this is changing, as brain imaging studies are now guiding behavioral research.

In the following sections, we will use well-established models of emotion regulation in adults as a framework to understand how emotion regulation develops during adolescence.

3. Models of Emotion Management

There are numerous ways to manage our emotional responses. A widely recognized approach, called the "process model" of emotion regulation, suggests that emotions and their regulation unfold in a specific sequence (see Figure 1a).

This model, proposed by James Gross, identifies several stages in the process. First, we encounter a situation that triggers an emotional response. This early emotional reaction often happens unconsciously and before we have time to think. As we become more aware of our emotions, we can start to actively manage the situation. We can choose to avoid certain situations (situation selection) or try to change aspects of the situation to minimize its emotional impact (situation modification). For example, someone with social anxiety might avoid social gatherings to regulate their anxiety. Next, we can use attentional deployment to shift our focus away from things that trigger unwanted emotions. Then, we consciously appraise and evaluate the emotional situation. We can engage in cognitive change, such as reappraisal, where we reinterpret the situation in a more positive light. Alternatively, we can use response modulation to directly influence our physiological, emotional, or behavioral reactions once they've been triggered. For instance, exercise and relaxation techniques can help decrease the physical and emotional effects of negative emotions. Another common response modulation strategy is expressive suppression, where we try to hide our emotional expressions. The process model also recognizes that our emotional responses can change the very situation that triggered them, implying that emotions and their regulation are constantly interacting and evolving.

While the process model helps us understand how well we implement emotion regulation strategies, it doesn't fully capture the complexity of adaptive emotion regulation, which involves choosing the right strategy for the situation. This realization led to the "extended process model" (see Figure 1b).

This model, developed by James Gross and others, suggests that emotion regulation happens in three stages:

1. Identification: Recognizing an emotional state and deciding whether to regulate it.

2. Selection: Choosing an appropriate regulation strategy.

3. Implementation: Putting the chosen strategy into action (this corresponds to the original process model).

Each stage involves three steps:

1. Perception: Noticing what's happening in the world around us.

2. Valuation: Judging whether it's good or bad.

3. Action: Doing something based on that judgment.

For example, during Identification, we might notice that we're feeling sad, decide that it's too intense, and choose to do something about it. This leads to the Selection stage, where we consider different regulation strategies, evaluate them, and take action by choosing the best one.

The extended process model raises intriguing questions about adolescent development. Do teenagers go through the perception-valuation-action cycle the same way adults do? Since social approval is very rewarding for adolescents, they might not feel the need to regulate their emotions in situations where they're seeking social rewards. Also, teenagers might face challenges during the Selection stage. While many emotion regulation strategies exist, adolescents may not be familiar with all of them, haven't practiced them enough, or lack the necessary advanced thinking skills and social understanding, which are still developing. This could limit their ability to effectively select and implement strategies compared to adults. Furthermore, developing executive functions might also affect their ability to switch strategies flexibly if the initial strategy doesn't work.

The development of executive functions and social cognition is also crucial during the Implementation stage. For example, cognitive reappraisal, where we reinterpret a situation to feel better, requires good working memory, verbal fluency, and, importantly, the ability to take another person's perspective. Imagine a teacher snapping at a student. A classic reappraisal strategy would be to think, "Maybe the teacher is just having a bad day." However, research shows that the ability to see things from other people's perspectives takes time to develop.

The following sections explore the development of emotion regulation and its neural underpinnings during adolescence, including the role of executive functions and social skills. Most studies have focused on the Implementation stage, where participants are given a strategy and researchers measure how well they use it. However, we'll also touch upon the Identification and Selection stages whenever possible.

We'll divide the discussion into implicit and explicit processes because the research methods used to study them are different. However, it's important to remember that this distinction is not always clear-cut, and there's likely overlap between implicit and explicit emotion regulation. For instance, some scientists believe that implicit emotion regulation might develop from repeatedly using certain explicit strategies.

4. Implicit Emotion Regulation

Implicit emotion regulation refers to any process that happens automatically, without conscious effort, to change the intensity, quality, or duration of an emotional response. While this definition includes the automatic use of strategies typically considered explicit, this section will focus on regulation happening in the very early stages of emotion perception and processing, even when individuals are not consciously aware of feeling an emotion.

Emotional stimuli, like a scary image or a smiling face, naturally grab our attention, especially by activating areas like the amygdala. This can be helpful because it prepares us to react quickly, like avoiding danger. However, constantly paying attention to every emotional cue can be overwhelming, especially for individuals with anxiety or depression who are more sensitive to negative emotions.

Thankfully, our brains have developed mechanisms to manage this. As emotional stimuli activate the brain's emotional centers, areas in the prefrontal cortex automatically step in to regulate these responses, especially when emotions might interfere with our goals. A recent study found that several brain regions, including the ACC, inferior frontal junction, dlPFC, and posterior medial OFC, work together to manage the interplay between emotional stimuli and cognitive control in adults.

It's no surprise that executive functions, those mental skills that help us control our thoughts and actions, are crucial for emotion regulation. We need good executive functions to remember our goals, predict outcomes, and plan our responses. Studies have shown that adults with better executive function, like being able to think of words easily (verbal fluency), are better at both increasing and decreasing their emotional responses. Recent research suggests that this might be true for adolescents as well. A study using questionnaires found that teenagers with better executive function were more likely to use reappraisal (reframing a situation to feel better), while those who relied on suppression (hiding their emotions) had poorer executive function, including difficulty with impulse control, problem-solving, and organization. These findings suggest a strong link between executive functions and emotion regulation.

Researchers often use tasks designed to measure executive functions to study emotion regulation as well. One such task is the go/no-go task, which measures attention and inhibitory control (the ability to stop ourselves from doing something). In this task, participants see a series of stimuli and have to press a button for most of them (go trials) but withhold their response when a specific stimulus appears (no-go trials). Since go trials are more frequent, this task measures how well someone can inhibit a dominant response. When emotional stimuli are used in this task, it becomes more challenging because emotions can interfere with our ability to control our responses. Therefore, slower reaction times on go trials or more errors on no-go trials might indicate difficulties with emotion regulation.

Another task that measures inhibitory control and attentional bias (paying more attention to certain things) is the Stroop test. In this task, participants see words printed in different colors and have to name the ink color while ignoring the word itself. The classic example is the word "red" printed in green ink. This task is challenging because reading words is automatic for most people. The emotional Stroop task is a variation where the words have emotional meanings. Research has consistently shown that people take longer to name the color of emotionally charged words, especially negative ones that are personally relevant (like words about cleanliness for someone with OCD), compared to neutral words.

Scientists have used brain imaging studies with variations of these tasks to understand how implicit emotion regulation develops in the brain during adolescence (see Table 1 for a summary). For instance, a study by Hare and colleagues used a modified go/no-go task where children (aged 7–12), adolescents (aged 13–18), and adults had to respond to fearful or calm faces. They found that children and adolescents were slower than adults in responding to fearful faces, suggesting that they were less effective at overriding the emotional interference. Brain imaging revealed that adolescents showed stronger amygdala activity than both children and adults when processing facial expressions, which might reflect ongoing development in this brain region.

This study has been followed up by several others. Tottenham and colleagues used a similar task with participants aged 5–28 and found that both emotion regulation and cognitive control improved with age. However, the gap between the two narrowed as people got older, meaning that adults were less affected by emotional information when trying to control their responses compared to children and adolescents.

Another study using a go/no-go task with happy and neutral faces found that adolescents (aged 13–17) made significantly more errors on no-go trials with happy faces compared to both children (aged 6–12) and adults (aged 18–29). This unique dip in performance during adolescence was accompanied by increased activity in the VS, a brain area associated with rewards. In contrast, activity in the IFG, a region involved in inhibitory control, increased with age. These findings support the idea that adolescent behavior might be more influenced by their brain's reward system while their prefrontal control system is still maturing.

It is important to note that recognizing facial expressions continues to develop during adolescence, with different emotions being recognized at different speeds. For instance, recognizing happy faces develops earlier than recognizing fear. This factor might partially explain the developmental differences observed in these studies. Some studies have tried to address this by examining inhibitory control in situations where emotions are irrelevant to the task.

For example, Cohen Kadosh and colleagues used a modified go/no-go task called the Overlap task to compare early (aged 11–12) and late (aged 17–18) adolescents. They found that early adolescents were disproportionately slower in responding to fearful faces compared to happy or neutral faces, suggesting poorer attentional control when processing fear. The authors proposed that this might be due to the ongoing maturation of the dlPFC. Interestingly, unlike the previous emotional go/no-go task, there were no age differences in accuracy, suggesting that age-related differences in inhibitory control during adolescence might be less apparent when emotions are not directly relevant to the task. This interpretation is supported by another study that directly compared different versions of the go/no-go task and found that only emotions relevant to the task significantly affected inhibition.

However, it's also possible that the development of inhibitory control in emotional contexts during adolescence is subtle and requires studying a large group of participants across the entire adolescent age range. This approach was taken by Cohen-Gilbert and Thomas, who studied 100 participants aged 6–25 using a go/no-go task where task-irrelevant background images (negative, positive, neutral, or scrambled) were presented with the target stimuli. They found that negative images disrupted inhibitory control specifically in adolescents aged 13–14 years (and girls aged 15–16). This suggests that even when emotional information is not directly related to the task, it can still interfere with self-control during early to mid-adolescence.

Another way to study inhibitory control in the context of emotion is to induce emotional states in participants. Perlman and Pelphrey used a go/no-go task where children (aged 5–11) and adults could earn points. The task was designed to induce frustration by making participants lose all their earned points. Brain imaging revealed distinct brain activity patterns in children and adults when they had to regulate their frustration. Importantly, the connection between the ACC and amygdala, two key regions for emotion regulation, became stronger with age, suggesting ongoing brain development in this network. Another study using a similar task with participants aged 5–16 found that adolescents, but not children, showed a specific brainwave pattern (N2 component) associated with inhibitory control after experiencing frustration.

During adolescence, peer relationships become increasingly important, and individuals become more sensitive to social acceptance and rejection. Based on this, Sebastian and colleagues used a variation of the emotional Stroop task with rejection-themed words. They found that mid-adolescents (aged 14–16) showed reduced activity in the right vlPFC, a region involved in emotion regulation, compared to adults when processing rejection words. This finding suggests that prefrontal regions responsible for regulating emotions continue to develop between mid-adolescence and adulthood.

Another study using the emotional Stroop task found that young adults (aged 23–25) showed greater activation in the dorsomedial PFC and precuneus (areas involved in attention and self-awareness) compared to late adolescents (aged 18–19) when processing negative words. This finding indicates that the maturation of brain systems involved in processing emotional information continues even into early adulthood.

While most research on implicit emotion regulation has focused on inhibitory control, there's also evidence suggesting that interactions between working memory (holding information in mind) and emotion processing continue to develop during adolescence. Ladouceur and colleagues used a task where participants had to remember sequences of items while ignoring distracting emotional faces. They found that older participants were faster at the task when fearful faces were present, but only if they were generally anxious. This highlights how individual differences in anxiety can impact emotion regulation during adolescence.

In conclusion, these studies provide valuable insights into the development of implicit emotion regulation from childhood to adulthood. They show that teenagers gradually get better at resisting emotional distractions and that this improvement is linked to brain development, particularly in areas responsible for controlling impulses and regulating emotions. However, some studies also suggest that emotion regulation during adolescence might follow a less straightforward path, with mid-adolescents sometimes showing more difficulty with emotional interference compared to younger children. These findings generally align with models emphasizing the ongoing development of prefrontal control regions and their connections with emotional centers like the amygdala. In essence, the ability to filter out emotional distractions and stay focused on goals continues to mature throughout adolescence. Next, we'll explore whether similar developmental patterns are observed for explicit emotion regulation.

5. Explicit Emotion Regulation

Unlike implicit strategies, explicit emotion regulation requires conscious effort and involves actively choosing and using strategies to manage our emotions. Two commonly studied strategies are cognitive reappraisal (reinterpreting a situation more positively) and expressive suppression (hiding our emotional expressions). A recent study by Lantrip and colleagues found that while adolescents' use of reappraisal was linked to better executive function, their use of specific strategies didn't change with age. However, another study with a larger group of adolescents found that the use of suppression decreased between ages 9 and 15. This finding makes sense because suppression is generally considered an unhealthy strategy linked to difficulties managing negative moods and experiencing positive emotions. As individuals mature and develop better executive function and social skills, they can learn alternative and healthier strategies.

Following this logic, we would expect the use of reappraisal to increase during adolescence. However, the evidence is mixed. While Gullone and colleagues found a decrease in self-reported reappraisal use between ages 9 and 15, Silvers and colleagues found that the ability to effectively use reappraisal in a lab setting improved with age in participants aged 10–23. It is important to note that these studies used different methods, age ranges, and definitions of reappraisal. Future studies should combine self-report and experimental measures of reappraisal use and success across adolescence to understand how this strategy develops.

Neuroscience research has begun investigating age-related differences in both spontaneous and instructed emotion regulation during adolescence. In a study by McRae and colleagues, participants aged 10–22 completed a reappraisal task while undergoing brain imaging. They found that reappraisal ability improved linearly with age and that this improvement was associated with increased activity in the left vlPFC, a brain area linked to cognitive control and reappraisal in adults. Interestingly, when not explicitly asked to reappraise, adolescents showed less activation in social cognition areas (like the medial prefrontal cortex, posterior cingulate, and temporal regions) compared to children and emerging adults. However, these regions were more active during reappraisal in adolescents compared to other age groups. This suggests that adolescents might not automatically engage in these social cognitive processes when not instructed but can do so when specifically asked.

Given that brain development during adolescence might influence emotional behavior, researchers are interested in understanding how structural brain changes relate to the development of emotion regulation strategies. Vijayakumar and colleagues conducted a longitudinal study where participants underwent brain scans at ages 12 and 16 and reported their use of reappraisal and suppression at age 19. They found that increased cortical thinning (which reflects maturation) in the left dlPFC and vlPFC was associated with greater reappraisal use at age 19, but only in females. This finding supports the idea that brain maturation in these areas might be important for using reappraisal effectively. The authors suggested that the absence of this finding in males might be due to sex differences in the timing of brain maturation. Previous studies have also shown that females might rely more on prefrontal regions for emotion regulation compared to males.

Most research on explicit emotion regulation in adolescents has focused on reappraisal and suppression because they are easy to study in a lab setting. However, some researchers argue that focusing on specific strategies might not accurately reflect how people regulate their emotions in everyday life. A study using experience sampling methods (where participants report their experiences at different points throughout the day) identified around 40 strategies that young adults used to regulate both positive and negative emotions. Similar studies have shown that adolescents use many of these strategies as well. However, it's still unclear whether adolescents have access to the same range of strategies as adults or how they decide when and how to regulate their emotions. Future research should explore these questions, considering the role of brain development, executive function, and social cognition.

Experience sampling has been used to study emotion regulation in adolescents for some time. Silk and colleagues asked adolescents to report their emotions, their intensity, and the strategies they used to regulate them throughout the day for a week. They found that using disengagement strategies (like denial or avoidance) or rumination (dwelling on negative thoughts) was associated with higher levels of depression and behavioral problems. It would be interesting to combine this ecologically valid approach with neuroimaging techniques to gain a more comprehensive understanding of emotion regulation in typical adolescents. As we'll see in the next section, some studies have already started exploring this by examining how brain responses in the lab relate to emotion regulation in everyday life, particularly in the context of mental health. Given that adolescence is a period of heightened emotional reactivity and that the teenage brain is still developing its emotion regulation abilities, understanding these links is crucial for preventing and treating mental health issues.

6. Understanding Emotions, the Teen Brain, and Mental Health

6.1. Internalizing symptoms

Mental health problems, particularly those involving internalizing symptoms like sadness and anxiety, become more common during adolescence. For example, the rate of depressive symptoms increases dramatically from early to middle adolescence. Teenagers struggling with internalizing problems like depression tend to use unhealthy emotion regulation strategies like self-blame and rumination and have difficulty using reappraisal. Recent neuroimaging studies have begun to shed light on the brain mechanisms associated with poor emotion regulation in adolescent depression.

These studies have mainly focused on reappraisal, an area where depressed adolescents often face challenges. Studies on adults with depression have found that they exhibit reduced activity in the dlPFC (a key area for cognitive control) and weaker connections between the PFC and amygdala when trying to reappraise negative emotions. These findings are consistent with research suggesting that successful reappraisal relies on the ability of prefrontal regions to regulate the amygdala and other areas involved in emotional responses. However, fMRI studies on depressed adolescents suggest a slightly different pattern.

Perlman and colleagues compared brain activity in depressed and non-depressed adolescents (aged 13–17) while they were asked to either maintain or reduce their emotional responses to negative images. They found that during the 'maintain' condition, depressed adolescents showed increased amygdala activity and weaker PFC-amygdala connectivity compared to controls. However, this pattern reversed during the 'reduce' condition, with depressed adolescents showing stronger connectivity when instructed to reappraise. This suggests that disrupted PFC-limbic circuitry might contribute to adolescent depression in some situations but might not be a constant feature.

A similar pattern was observed in a study using a more realistic "chatroom" task where adolescents experienced social rejection from virtual peers. Given that peer rejection is a common experience during adolescence and has been linked to depression, understanding how teenagers regulate their emotions in such situations is important. Platt and colleagues instructed depressed and non-depressed adolescents (aged 15–17) to either pay attention to or reappraise instances of social rejection. While both groups successfully used reappraisal to reduce negative emotions, the depressed group showed increased connectivity between the right frontal pole (another area involved in cognitive control) and the amygdala and hippocampus (regions involved in emotion and memory) specifically during reappraisal. These findings suggest that the neural mechanisms of emotion dysregulation in adolescent depression might differ from those in adults. Future research should directly compare depressed adolescents and adults to confirm these findings.

Platt and colleagues speculate that the increased connectivity observed during reappraisal in depressed adolescents might reflect their ability to compensate for existing emotion regulation difficulties by using cognitive strategies. This suggests that reappraisal training could be a promising approach for treating adolescent depression.

Several studies have also examined how typically developing adolescents respond to peer rejection in the absence of explicit instructions to regulate their emotions. While participants in these studies were aware of being rejected, they were not told how to manage their emotions. Therefore, any regulation observed would be considered spontaneous.

Masten and colleagues used the "Cyberball" paradigm, a virtual ball-tossing game designed to induce feelings of social exclusion. They found that brain activity in the subgenual ACC during social exclusion predicted depressive symptoms one year later in a group of 13-year-olds. This finding is particularly interesting because increased activity in this brain region has been linked to both depression and heightened sensitivity to peer rejection in adolescents. Future studies could explore whether teaching emotion regulation strategies like reappraisal can influence activity in this brain region and potentially reduce the risk of depression.

6.2. Externalizing Symptoms

While some individuals develop conduct disorder (a pattern of violating rules and rights of others) before age 10, most externalizing symptoms, such as physical aggression, theft, property damage, and truancy, emerge during adolescence. Aggression can be categorized as either reactive or proactive. Reactive aggression is an impulsive response to provocation or frustration and is linked to poor impulse control. Proactive aggression, on the other hand, is planned and goal-directed and is associated with callous-unemotional traits in children and adolescents. While poor emotion regulation is more strongly associated with reactive aggression, both types are often correlated, and proactive aggressors often have low frustration tolerance.

Neuroimaging research on conduct problems in adolescence is still in its early stages. One study by Viding and colleagues found that adolescents with conduct problems who displayed low levels of callous-unemotional traits (suggesting more reactive aggression) showed heightened amygdala activity when implicitly shown fearful faces. This finding suggests an exaggerated automatic response to emotional cues in this group, possibly reflecting an attentional bias towards threat. This heightened sensitivity to threat is a hallmark of several mental health issues, including anxiety, PTSD, and reactive aggression. However, this study didn't specifically examine emotion regulation mechanisms.

Sebastian and colleagues addressed this gap by studying adolescents with conduct problems using an implicit emotion regulation task. Participants had to make a perceptual judgment (detecting a blue dot) while being presented with fearful or calm faces. Crucially, when the blue dot was present, it was either placed on the eyes (a highly salient area for interpreting fear) or elsewhere on the face. They found that adolescents with conduct problems and low callous-unemotional traits were disproportionately slower in detecting the blue dot when it was placed on fearful eyes compared to typically developing adolescents. This slower reaction time was associated with increased left amygdala activity. Additionally, this group showed greater activity in the subgenual ACC and OFC, regions involved in attention to emotions and integrating emotions with cognitive control, when processing fearful eyes compared to controls. These findings suggest that emotional information might interfere more with executive processes in adolescents with reactive aggression.

If impaired prefrontal-limbic control contributes to reactive aggression, we would expect improvements in these brain regions to accompany symptom reduction. Lewis and colleagues investigated this hypothesis using a go/no-go task designed to elicit frustration in children (aged 8–12) with externalizing and internalizing symptoms. Participants completed the task before and after a 14-week intervention program that included elements of cognitive behavioral therapy and parent training. Following treatment, children who showed behavioral improvements also exhibited normalization of their N2 brainwave, which is generated by the ventral frontal regions and reflects inhibitory control. Interestingly, this normalization involved a reduction in the N2 amplitude. The authors suggest that before treatment, these children might have relied on an inflexible, threat-focused regulatory style that generated an exaggerated N2 response. Although preliminary, this study highlights that interventions aimed at reducing externalizing symptoms might also improve neural mechanisms involved in implicit emotion regulation. Future research should explore whether directly training these neural circuits could lead to positive behavioral changes.

7. Conclusions

The study of emotion regulation during adolescence has gained significant momentum in recent years, largely due to groundbreaking discoveries about the ongoing development of brain regions responsible for regulating emotions during this period. This review aimed to connect models of brain development with models of emotion regulation, highlighting the complex interplay between these processes. It's highly likely that all stages of emotion regulation (identification, selection, and implementation) continue to develop throughout adolescence. However, most studies to date have focused on the implementation stage.

Some evidence suggests that both behavioral performance and brain activity during implicit emotion regulation tasks might follow a non-linear developmental trajectory, with mid-adolescents sometimes exhibiting greater sensitivity to emotional information compared to younger and older individuals. These findings seem to support the idea that uneven brain development during adolescence can influence behavior. However, it's crucial to remember that the relationship between brain structure, function, and behavior is not always straightforward.

Regarding explicit strategies like reappraisal, findings are mixed. Some studies show increased use of this strategy throughout adolescence, which aligns with the notion that reappraisal use might improve as executive functions, verbal abilities, and social cognitive skills develop. However, other studies suggest that instructed reappraisal use in the lab might not translate to increased spontaneous use in everyday life. Given the limited research in this area, methodological differences between studies make it challenging to draw definitive conclusions. Future research should address these limitations by using consistent methods, larger sample sizes, and a wider age range.

As more research emerges, it will be crucial to synthesize findings through meta-analyses. Furthermore, understanding the relationship between neural mechanisms of emotion regulation and the emergence and prevention of mental health problems is crucial. Given the plasticity of the adolescent brain, this period presents a unique opportunity for interventions that could promote healthy emotion regulation and potentially prevent mental health issues from escalating.

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1. Introduction

Our emotions are like waves in the ocean, sometimes calm and sometimes rough. Just like we learn to surf, we also learn to manage our emotions, which is called emotion regulation. We can do this without even realizing it, like when we automatically calm down after a friend makes us laugh. This is called implicit emotion regulation. We can also use our thoughts and actions to change how we feel, like when we take deep breaths to calm down when we're upset. This is called explicit emotion regulation.

Being a teenager (ages 10-19) is full of big changes like growing taller, becoming more independent, dealing with schoolwork, and navigating friendships. These changes can bring lots of emotions! Scientists believe that because teenagers' brains are still developing, they might find it a bit harder to manage their emotions compared to adults. This can sometimes lead to feeling more anxious or stressed.

This article will explore how emotion regulation develops during the teenage years. We'll look at how the brain changes and learn about different ways teenagers manage their emotions, both automatically and on purpose.

2. The Teenage Brain: A Work in Progress

Have you ever noticed how you get better at things like riding a bike or playing video games the more you practice? Our brains are similar! During our teenage years, our brains go through amazing changes, especially the part at the front called the prefrontal cortex (PFC). The PFC helps us make plans, control our impulses, and manage our emotions. Think of it as the brain's control center!

Imagine the PFC as a garden. During childhood, the garden is full of new plants and flowers (connections in the brain) growing everywhere. As we become teenagers, gardeners (brain development) come in and start trimming the garden, removing extra plants and making space for the remaining ones to grow stronger. This "trimming" process is called synaptic pruning, and it helps our brains work more efficiently.

At the same time, other parts of the brain involved in emotions, like the amygdala (which helps us understand and respond to fear and other strong emotions), are also developing. Sometimes, the amygdala might react more strongly to emotions in teenagers compared to adults, like a smoke alarm going off for a small puff of smoke. This is because the PFC, the brain's control center, is still being "trimmed" and getting better at its job of managing those strong emotions.

Scientists have different ideas about how these brain changes affect teenagers' emotions and behavior. Some believe that the PFC, being a bit slower to develop, might not be able to control the amygdala's strong reactions as effectively, leading to more impulsive behaviors or stronger emotional responses.

3. Understanding How We Manage Our Emotions

Imagine you're about to give a presentation in class. Your heart might start racing, and you might feel butterflies in your stomach. This is your body's natural reaction to feeling nervous. But how do you deal with these feelings? Do you try to avoid eye contact and rush through your presentation? Or do you take deep breaths, remind yourself that it's okay to be nervous, and focus on sharing your ideas?

Scientists have developed models to understand how we manage our emotions. One model, called the Process Model, says that we go through different steps when dealing with our emotions, starting from when we first encounter a situation to how we react and then try to manage those reactions.

A newer model, called the Extended Process Model, adds more steps to this process. It suggests that we first need to recognize that we're experiencing an emotion and decide if we need to manage it. Then, we have to choose a strategy to manage that emotion, and finally, we put that strategy into action.

Think about the presentation example again. First, you recognize that you're feeling nervous (Identification). Then, you decide that you want to calm down (Selection). Finally, you take deep breaths and remind yourself that it's okay to be nervous (Implementation).

4. Automatic Emotion Control: Like a Reflex!

Sometimes, we manage our emotions without even realizing it. This is called implicit emotion regulation. It's like a reflex—we don't have to think about it; it just happens.

Remember the example of the amygdala acting like a sensitive smoke alarm? Well, the PFC, even though still developing, can learn to quickly respond to the amygdala's signals and calm things down.

Scientists use different tasks to understand how teenagers get better at this automatic emotion control. One task is called the go/no-go task. Imagine playing a game where you have to press a button every time you see a picture of a cat (go) but not when you see a picture of a dog (no-go). This game requires you to control your impulses and stop yourself from pressing the button when you see a dog.

Now, imagine playing this game while also seeing pictures of happy or scared faces. It becomes a bit harder to focus, right? This is because those emotional faces can distract us, especially if we're already feeling anxious or stressed.

Studies using the go/no-go task and brain scans have found that teenagers generally get better at controlling their impulses and ignoring distractions as they grow older. However, some teenagers might find it more challenging to ignore emotional distractions, especially during middle adolescence, when the PFC is still undergoing those "trimming" changes.

5. Effortful Emotion Management: Choosing Your Strategies

In addition to automatic emotion control, we also use explicit emotion regulation, which involves consciously choosing strategies to manage our emotions. Two common strategies are reappraisal, where we try to change how we think about a situation, and suppression, where we try to hide our emotions.

Let's say you fail a test. You could use reappraisal and tell yourself, "It's okay, it's just one test, and I'll study harder next time." Or you could use suppression and try to hide your disappointment by pretending you don't care.

Studies show that teenagers tend to use suppression less as they get older, which is a good thing because suppression can make it harder to cope with negative emotions in the long run. Instead, teenagers, as their brains develop and they gain more experience, learn to use more helpful strategies like reappraisal.

However, learning to use reappraisal effectively takes time and practice. It requires us to control our thoughts and see situations from different perspectives, which are skills that improve with age and experience.

Brain imaging studies have shown that when teenagers use reappraisal, they activate the PFC, the brain's control center, more than younger children. This suggests that teenagers are learning to use their PFC to manage their emotions more effectively, even if it's still a work in progress!

6. Emotion Regulation and Mental Health

Sometimes, teenagers might face bigger challenges in managing their emotions. This can happen for different reasons, such as genetics, life experiences, or difficulties in how their brains are developing. When teenagers struggle with their emotions for a long time, it can lead to mental health challenges like depression or anxiety.

6.1. Depression: When Sadness Lingers

Depression is more than just feeling sad; it's like feeling a heavy weight in your chest that makes it hard to enjoy things you used to love. Teenagers with depression might struggle to manage negative emotions and get stuck in a cycle of negative thoughts. They might blame themselves for things they can't control or have trouble seeing the positive side of things.

Brain imaging studies have shown that teenagers with depression sometimes have differences in how their PFC and amygdala communicate with each other. This can make it harder for them to regulate their emotions, especially when trying to use strategies like reappraisal.

6.2. Externalizing Problems: Outward Expressions of Difficulty

Some teenagers might express their emotional struggles through their behavior, like getting angry easily, having trouble following rules, or getting into fights. This is often called "acting out" or having "externalizing problems."

Just like with depression, brain imaging studies have shown that teenagers with externalizing problems might have differences in their brain activity, particularly in regions involved in controlling impulses and managing emotions.

The good news is that just like we can train our bodies to become stronger and faster, we can also train our brains to become better at managing emotions! There are effective therapies, like cognitive behavioral therapy (CBT), that help teenagers learn helpful thinking patterns and coping strategies.

7. Conclusion: A Lifetime of Learning

Learning to manage our emotions is a lifelong journey, and adolescence is a crucial time for developing these skills. The teenage brain is constantly changing, adapting, and growing, and with it, our ability to understand and manage our emotions improves.

Scientists are still unraveling the complexities of the teenage brain and how it influences emotion regulation. However, we already know that teenagers are capable of learning and using a variety of strategies to navigate the ups and downs of their emotional world.

By understanding how our brains develop and learning healthy coping mechanisms, teenagers can build a strong foundation for emotional well-being that will serve them throughout their lives.

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