1. Introduction

Anxiety often manifests in adolescence, with over 31 % of US adolescents reporting symptoms of anxiety (Lee et al., 2006; Merikangas et al., 2010) which have been linked to a pattern of behavioral avoidance in youth (Galván and Peris, 2014; Reniers et al., 2016) and adults (Maner and Schmidt, 2006). Contrasting with this risk-averse phenotype are the typical hallmarks of adolescence such as increased risk taking and exploration, crucial aspects of healthy development (Casey et al., 2008) that can be observed across species (Brenhouse and Andersen, 2011; Steinberg, 2008) and cultures (Duell et al., 2018).

Why does this developmental period give rise to seemingly contrasting phenotypes: an increase in anxiety symptomatology characterized by avoidance and inhibition and an increase in risk taking characterized by approach behaviors? Here, we review the current literature and integrate research examining the neural correlates of anxiety and risk taking in an effort to achieve a deeper understanding of the mechanisms underlying anxiety in youth who are afflicted with symptoms at odds with typical adolescent development. We also highlight the adaptive nature of adolescent risk taking as a means of promoting independence, learning, and goal-directed behavior (Casey et al., 2008; Spear, 2000), important facets of adolescent development that are impeded by anxiety and its corresponding patterns of behavioral avoidance.

Ultimately, this paper will argue that the study of adolescent-onset anxiety demands consideration of the concurrent development of approach and avoidance systems and their influence on typical adolescent behaviors (e.g., risk taking). This is a departure from extant research that has studied each of these constructs (approach and avoidance) separately, particularly in the context of anxiety. Future longitudinal studies tracking the interactions between and regulation of approach and avoidance motivations across typical and atypical development are needed to achieve a deeper understanding of the heterogeneity in adolescent anxiety, to identify vulnerable adolescents, and to develop effective interventions for at-risk youth.

2. The development of anxiety

2.1. Background

The experience of anxiety is a normative and evolutionarily adaptive response to stressful environmental stimuli (e.g., potential threats). Rooted in the feeling of fear, anxiety triggers behavioral avoidance, which can promote safety by motivating escape from danger (Beesdo et al., 2009). While avoiding threatening stimuli is adaptive early in development (Shechner et al., 2012), a pattern of behavioral avoidance can preclude the opportunity for fear extinction and become reinforcing and habitual (LeDoux et al., 2017), resulting in impaired functioning and increased vulnerability to further anxiety (Arnaudova et al., 2017). This is especially worrisome in adolescence, a period when youth often begin to exhibit increases in risk-taking behaviors and social interaction that are critical for independence in adulthood (Casey et al., 2008).

The average age of onset for most anxiety disorders is in early adolescence (Kessler et al., 2007), with over 31 % of US adolescents meeting clinical threshold for a disorder (Merikangas et al., 2010) and countless others experiencing normative symptoms of anxiety (Beesdo et al., 2009; Siegel and Dickstein, 2011) which have been linked to negative outcomes such as depression, addiction, educational underachievement, and suicide (Chiu et al., 2016; Kendall et al., 2018; Siegel and Dickstein, 2011; Woodward and Fergusson, 2001). Despite a 17 % increase in youth anxiety disorder diagnosis over the past decade (Child Mind Institute, 2018), the majority of anxiety disorders in developing youth remain undiagnosed and untreated (Benjamin et al., 1990; Child Mind Institute, 2018; Green et al., 2019; Merikangas et al., 2010; Siegel and Dickstein, 2011). Instead of cognitive or conscious endorsement of anxiety symptoms, youth often demonstrate behavioral and somatic manifestations of the symptoms themselves (e.g., stomach aches; Siegel and Dickstein, 2011). As routine medical visits often decrease after childhood, ambiguous symptoms can be easy to miss (Siegel and Dickstein, 2011), and data suggest that youth ages 12–17 with anxiety are more likely to have an unmet health need (specifically in mental health care and wellness checkups) than those without anxiety symptoms (Green et al., 2019).

Before noticeable anxiety symptoms emerge, youth often demonstrate attention biases that can manifest as early as infancy and guide learning and behavior, thereby providing a useful marker for the development of anxiety (Shechner et al., 2012). A key predictor of adolescent anxiety is a childhood pattern of behavioral inhibition (BI) that is characterized by fear, wariness, and avoidance of unfamiliar stimuli such as new people or situations (Fox et al., 2005; Broeren et al., 2013; Domschke and Maron, 2013; Henderson et al., 2015). Inhibited children are almost four times as likely as those without BI to develop anxiety disorders in adolescence (Chronis-Tuscano et al., 2009; Essex et al., 2010; Schwartz et al., 1999); however, not all individuals with BI go on to develop anxiety later in life (Henderson et al., 2015). Therefore, a thorough examination of risk and resilience in this high-risk group is crucial for understanding and preventing the development of anxiety in adolescence.

Throughout development, anxiety is thought to affect neural functioning through an atypical modulation of attention by, or an attentional bias towards, threats and fearful stimuli. This is supported by neuroimaging studies in populations with both clinical and non-clinical anxiety that have highlighted atypical functioning of what is generally referred to as the “salience network” of the brain, comprised of regions such as the threat-sensitive amygdala and the regulatory prefrontal cortex (PFC) that together are involved in controlling attention and response to threat (for full review, see Blackford and Pine, 2012). However, altered threat processing is not the only signature of anxiety; a smaller body of research has also documented biased reward processing and atypical functioning of reward-related regions such as the striatum in anxious and at-risk youth (Guyer et al., 2006; Lahat et al., 2018). A closer look at the concurrent development of threat- and reward-processing neural networks in at-risk youth is necessary to understand how, why, and which individuals transition from normative to clinical anxiety in adolescence.

2.2. Puberty and the adolescent brain

The transition from childhood to adolescence represents a high-risk phase for the development of anxiety. The beginning of puberty triggers an overproduction of axons and synapses across the brain, which is followed by a pattern of rapid pruning later in adolescence (Crews et al., 2007). During this period, subcortical regions involved in processing reward and threat such as the ventral striatum (VS) and amygdala are hyperactive in response to stimuli, increasing desire and sensitivity for positive feedback (Galván, 2013). Simultaneously, regulatory systems in the prefrontal cortex (PFC) are still maturing (Casey et al., 2008). The differential developmental trajectories of these dynamic systems is thought to underlie the drive for exploration and risk taking—in addition to the vulnerability for negative outcomes—in adolescence (Casey and Jones, 2010; Galvan et al., 2006).

The neurobiology of adolescent motivated behavior has been explained by the Triadic Model, in which three neural systems—approach, avoidance, and regulatory—interact and compete to influence response to positive and aversive cues (Ernst et al., 2009). This model posits that while adolescents demonstrate increased striatal response to positive stimuli and increased amygdala response to negative stimuli, when appetitive and aversive stimuli are pitted against each other, regulatory systems will bias behavior towards approach responses in adolescents compared to adults (Ernst et al., 2009). This model provides a promising framework for the study of adolescent-onset anxiety, as the reciprocal roles of the striatum and amygdala in decision making is of particular relevance to the development of anxiety in youth. The fact that both reward- and threat-related systems exhibit continued development that often manifests as enhanced excitability in adolescence adds complexity to the behavioral patterns observed during this developmental period.

Previous work examining VS function during adolescence has primarily focused on its association with reward. The dopamine (DA) system, which coordinates excitatory and inhibitory neural activity, undergoes changes in the striatum during adolescence (Ernst et al., 2009; Galvan, 2010). Higher dopamine levels and greater dopaminergic response to reward in the VS have been associated with higher sensation-seeking tendencies such as increased risk taking (Derringer et al., 2010; Riccardi et al., 2006; Zuckerman, 1985). Furthermore, adolescents demonstrate heightened VS activity in response to rewards compared to children or adults (Galvan, 2010).

More recently, the role of the striatum has also been implicated in fear processing and anxiety. The striatum becomes sensitized at the same developmental timepoint when anxious symptomatology first manifests. Furthermore, the striatum is closely interconnected with the amygdala, hippocampus, and ventromedial PFC—all key players in adolescent anxiety—and is known to be highly involved in motivation, conditioning/prediction error, and attention (Lago et al., 2017). Pre-clinical animal models have demonstrated that the VS (e.g., nucleus accumbens; NAcc) is necessary for scaling fear to degree of threat: adult rats with NAcc lesions showed specific impairments in rapid uncertainty-safety discrimination, a skill that is necessary for survival and disrupted in clinical anxiety (Ray et al., 2020). While future work is needed to examine whether this association holds in juvenile rats, the striatum has also been linked to anxiety in humans; anxious youth show greater striatal response to low- rather than high-valued outcomes, perhaps due to the relative level of potential risk associated with each option, in addition to demonstrating increased VS activity during feedback anticipation (Benson et al., 2014). Furthermore, an intolerance of uncertainty—a common feature of anxiety (Dekkers et al., 2017; Osmanağaoğlu et al., 2018)—has been positively associated with striatal volume (Kim et al., 2017).

Altered striatal functioning has also been highlighted in studies of at-risk youth. Research examining reward processing in behaviorally inhibited adolescents has found that adolescents with BI—who demonstrate increased amygdala activity during threat processing—also demonstrate increased striatal activity during reward processing (Guyer et al., 2006; Lahat et al., 2018). Similarly, early life adversity has been associated with altered response to both positive and aversive cues across species (Nelson et al., 2009) as well as alterations in both amygdala and striatal development that together affect learning and mental health (Fareri and Tottenham, 2016), rendering a thorough investigation of both the amygdala and the striatum crucial for the study of anxiety across development.

The adolescent striatum receives input from the amygdala (Haber and Behrens, 2014), allowing it to translate evaluative signals into value-based action (e.g., approach or avoid; Fareri and Tottenham, 2016). The connections between these regions are crucial for affective development and may be disrupted in anxiety, as behaviorally inhibited individuals demonstrate reduced amygdala-striatal resting state connectivity (Roy et al., 2014). Furthermore, animal work suggests that amygdala-striatal communication plays a crucial role in motivated behavior, as flow of information between the amygdala and the NAcc is necessary for active avoidance behavior in rats (Ramirez et al., 2015). While studies of risk taking often focus on the reward-seeking VS and the regulatory PFC, it is imperative to consider how reward-related processes interact with the similarly sensitive threat reactivity of the adolescent amygdala. Conversely, while the increase in adolescent anxiety has been linked to the contrasting developmental trajectories of the threat-sensitive amygdala and the regulatory PFC, it is important to consider how the VS works in tandem with the amygdala to impact adolescent decision making.

2.3. Risk taking and anxiety

While aberrations in approach and avoidance motivations have been linked to both maladaptive risk taking (e.g., substance abuse; Casey and Jones, 2010) and affective disorders (e.g., anxiety; Arnaudova et al., 2017), there is currently a dearth of studies documenting risk taking in anxious adolescents. Furthermore, the extant research has primarily focused on “dangerous” risk taking (e.g., substance abuse) in anxiety, with less emphasis placed on adaptive risk-taking behaviors that might be beneficial for adolescent development (Duell and Steinberg, 2019). While the characterization of anxiety phenotypes often focuses on risk aversion (Sonuga-Barke et al., 2016), the heterogeneity of the disorder and its interaction with typical adolescent development adds complication to this narrative.

While some studies have found that anxious adolescents are at reduced risk for substance abuse due to their risk aversion (Malmberg et al., 2010), others have reported an increased risk in this population (Child Mind Institute, 2018; Kilgus and Pumariega, 2009; Low et al., 2008). Sex and gender differences may contribute to this variability in behavior; female adolescents tend to demonstrate stronger associations between anxiety and drug and alcohol use than males (Cruz et al., 2017; Wu et al., 2010).

Evidence also suggests the existence of anxiety subtypes with distinct behavioral profiles. In one study, researchers identified two subtypes of social anxiety: one characterized by the typical behavioral inhibition and risk avoidance, and the other—deemed the “approach-motivated” subtype—by impulsiveness, reward sensitivity, risk taking, and substance abuse (Nicholls et al., 2014). Another study tested a genetic moderator of loss aversion and impulsivity in anxious adolescents and found that high expression of a specific gene variant was linked to a behavioral profile characterized by low loss aversion and high impulsivity, suggesting a genetic marker of increased proclivity for risk taking in anxious youth (Ernst et al., 2014).

Understanding different behavioral profiles of adolescent anxiety is especially important given the implications of risk taking and mental health for the juvenile justice system. Symptoms of anxiety and depression are common in juvenile offenders (Cauffman, 2004) and may influence offending behaviors in justice-involved youth (Copeland et al., 2007; Hoeve et al., 2013); however, mental health needs in this population are often left unmet (Zajac et al., 2015). Taken together, these results underscore the importance of considering risk-relevant traits such as impulse control and reward sensitivity (in addition to threat sensitivity) in studies of adolescent anxiety.

2.4. Threat vs. thrill

Risky decision-making does not always necessitate the potential for a tangible reward. Instead, the presence of potential threat in a situation may be the very aspect that ignites reward-related circuitry (and the corresponding rewarding feelings) within an adolescent brain. Whether riding a roller coaster, jumping out of an airplane from 12,000 feet in the air, or forgoing a helmet on the last leg of a bike journey, potential threat can evoke strong and exciting sensations that mimic the feelings of reward in individuals of all ages (Spielberg et al., 2014). For example, a program called “Adrenaline Instead of Amphetamine” found that men addicted to stimulating psychoactive drugs such as amphetamine could be effectively treated by engaging in legal and more benign thrills such as sky diving (Makarowski et al., 2016); in other words, the adrenaline produced by potential threat could mimic the rewarding feelings of illicit drug use on the human brain. While the efficacy of this therapy has only been tested in adults, future work might benefit from employing a similar treatment strategy in a younger population.

Due to the disparate development of threat, reward, and regulatory systems, risking danger may be uniquely thrilling in adolescence compared to in other stages of life (Dahl, 2004). The sensation of thrill is involved in many aspects of adolescent risk taking, including romance and sexual experimentation. As the idea of “butterflies in the stomach” suggests, social interaction in adolescence can be as much rewarding as it is acutely terrifying. In order to explore and learn from new and potentially scary experiences, it would greatly behoove the adolescent brain to have a nuanced perception of threat that can perceive danger as both frightening and rewarding. Previous research provides initial support for this theory, as adolescents tend to be more tolerant of uncertainty during risky decision-making than either children or adults (Van Den Bos and Hertwig, 2017) and are more willing to take risks when the risk is ambiguous rather than when risks are clearly stated (Tymula et al., 2012).

Whereas risk-taking behaviors have been associated with a tolerance of uncertainty (Blankenstein et al., 2016), symptoms of anxiety are often linked to an intolerance of uncertainty (Dekkers et al., 2017; Osmanağaoğlu et al., 2018). In a study of unmedicated anxious adults, researchers tested whether risk avoidance in anxiety was driven by risk aversion—an intolerance of uncertain outcomes—or an attentional bias towards potential loss. Risk avoidance was linked to increased risk sensitivity, while loss sensitivity was equivalent across anxious and control groups (Charpentier et al., 2017). This suggests that, regardless of likelihood of loss, perhaps the very aspect of risk that is thrilling for healthy adolescents—that inherent uncertainty of the outcome—is interpreted as threat in anxious adolescents. Future studies documenting risk taking in anxious youth are necessary to understand how adolescent changes in tolerance of uncertainty influence trajectories of anxiety development.

In an attempt to test whether threat becomes uniquely rewarding during puberty, Spielberg and colleagues found that increased amygdala response to threat over time was associated with higher sensation seeking and lower anxiety in individuals who also demonstrated increased VS response to threat over time (Spielberg et al., 2014). Another study providing evidence for the potentially rewarding aspects of threat in adolescence examined learning and neural response in conditions involving evaluation threat. In this study, striatal activity during learning under evaluation threat tracked performance such that adolescents demonstrating increased striatal activity also demonstrated increased learning, a unique pattern that was not seen in adults (Depasque and Galván, 2019). These findings add nuance to a seminal study of reward processing and anxiety that found that adolescents with a history of BI demonstrated increased striatal response during decisions in which the outcome was contingent on participant response (Bar-Haim et al., 2009). How might anxiety impact striatal response to evaluation threat—and would this brain response be conducive or detrimental to learning?

Understanding the influence of amygdala-striatal interactions on adolescent behaviors and mental health across development holds great promise for tailored and effective intervention in adolescence. Perhaps amygdala reactivity can promote approach over avoidance behaviors when combined with VS activity, and promoting positive risk taking by linking threat to reward could help prevent the manifestation of anxiety in adolescence. Previous research suggests that reward-based training may be effective in reducing anxiety and—importantly—has lower risk of exacerbating future anxiety than threat-related treatments (Dandeneau and Baldwin, 2009). If the hyperactive striatum in adolescence is driving adolescents to engage and persevere in learning under threat, perhaps it works in tandem with the amygdala in a similar fashion to reinterpret threat and encourage learning during risky decision-making. An examination of the development of both reward and threat systems simultaneously—and their contributions to risk taking and learning—is imperative.

3. Measuring meaningful change

3.1. A need for longitudinal studies

While neural signatures of both clinical and non-clinical anxiety have been examined in youth, research has yet to capture the transition from normative to clinical anxiety in adolescence from a neurobiological perspective. Cross-sectional studies in childhood and adolescence have helped the field identify which neural regions underly typical anxiety phenotypes and have provided snapshots of neural development across different individuals at varying ages. However, in order to examine the interactions between fronto-amygdala-striatal circuits across adolescence and their relevance for normative and clinical anxious trajectories, longitudinal studies in youth across the anxiety continuum are crucial for accurately tracking developmental change.

Longitudinal studies also allow researchers to track the development of parallel processes in adolescence that may be bidirectionally associated with the development of anxiety. For example, sleep difficulties—which are common in adolescence—are often a precursor of anxious symptoms, can prospectively predict worsening anxiety, and may be especially impactful to mental health in early adolescence (McMakin and Alfano, 2015). Similarly, poor sleep has been associated with increases in both symptoms of anxiety (Kelly and El-Sheikh, 2014) and risk-taking behaviors (Baker et al., 2020; Telzer et al., 2013). Tracking the interactions between sleep difficulties and symptoms of anxiety as youth enter adolescence would provide valuable insight into the development of anxiety and potential interventions for at-risk youth.

3.2. Neuroimaging methods

3.2.1. Dynamic causal modeling (DCM)

The majority of current knowledge regarding brain development and neural signatures of anxiety disorders in youth focuses on correlational associations (e.g., heightened amygdala activity correlating with anxiety severity or reduced PFC functioning in anxious youth during the viewing of emotional images). However, this precludes identification of how these brain regions influence each other to affect adolescent behavior and mental health. Is it an overactive threat response in the amygdala, constant over-regulation in the PFC, or competing influences of the amygdala and VS that drive the feeling of anxiety?

Future studies would benefit from consideration of methods such as Dynamic Causal Modeling (DCM), which allow inference of causal architecture between related brain regions (e.g., amygdala, PFC, and VS) by measuring effective connectivity between brain regions to estimate how neuronal changes in one region influence activity in another region. This method is promising for developmental samples, as it has the potential to capture complex associations of competing brain networks that are continuously reshaped over development (Goldenberg and Galván, 2015). With this approach, one can answer targeted questions regarding the dynamic chain of events underlying adolescent decision making.

3.2.2. Reliability

Despite the promise of longitudinal neuroimaging research for tracking developmental change, it is important to consider the test-retest reliability—or the consistency of an assessment tool to produce stable results with each use (Khoo et al., 2007)—of neuroimaging methods in developmental and at-risk populations (for full review, see Herting et al., 2018). Without establishing reliability, delineating true developmental change from changes based on extraneous factors such as noise or artifact becomes difficult. Imaging modalities vary in their reliability; for example, structural indices of brain maturation such as grey matter measurements, white matter volume, and diffusion tensor imaging (DTI) have been shown to be highly reliable across scans in youth (Drobinin et al., 2020), while task-based fMRI demonstrates good reliability for some regions (e.g., occipital lobe) and lower reliability in subcortical areas such as the amygdala and the VS (Vetter et al., 2017). The chosen analysis method can also influence reliability; in addition to its analytic benefits, DCM demonstrates relatively high reliability between scan sessions (Frässle et al., 2015; Schuyler et al., 2010).

Tangible steps towards improving reliability in developmental samples include reducing motion in the scanner (e.g., by prioritizing participant comfort and offering breaks), structuring additional test-retest scans into the protocol with minimal time between measurements, and utilizing multiple imaging modalities in acquisition, processing, and analysis (Herting et al., 2018). For example, studies combining anatomical and functional markers of neural connectivity (e.g., DTI and fMRI, respectively) have elucidated crucial information regarding the development and maturation of brain networks in children (Supekar et al., 2010), and brain-based age prediction has been shown to improve when using multimodal neuroimaging data (Liem et al., 2017). Overall, utilizing multimodal imaging provides a rich and multidimensional view into the developing brain, while the combination of various sources of measurement mitigates risk for spurious, noise-based findings.

Finally, a strong strategy for increasing replicability and generalizability of findings is to recruit a large, diverse participant sample. Smaller sample size increases the chance of spurious or non-generalizable findings, and even a minimum of 100 participants can fall short of perfect reliability (Turner et al., 2018). A thorough and well-powered examination of individual differences in the developmental risk for anxiety requires adequate sampling from a diverse pool of youth across a continuum of anxiety.

4. Conclusion

Anxiety is common among many developing youth, greatly impairs functioning, and only tends to worsen in severity following adolescence (Beesdo et al., 2009; Bittner et al., 2007; Broeren et al., 2013; Kessler et al., 2007; Merikangas et al., 2010). Furthermore, the threat-related brain processes identified in anxiety directly conflict with typical adolescent behaviors such as increased risk taking and exploration (Casey et al., 2008). How does the simultaneous development of fronto-amygdala and fronto-striatal circuits affect attention and anxiety in adolescence? Are anxious youth who demonstrate concurrent activity in the amygdala and the VS during risk taking more prone to risky behavior, thereby achieving a more normative functioning in adolescence? Examination of this adolescent paradox—the rise of both sensation seeking and anxiety in adolescence—is crucial for answering the open questions regarding how anxiety manifests in adolescence, and for identifying targeted and effective methods and timepoints for treatment. A prospective longitudinal study of youth at risk for anxiety that tracks approach and avoidance motivations, risk taking, and mental health in the journey through puberty is necessary to answer these crucial questions regarding risk and resilience and to aid adolescents tormented by clinical anxiety.

Link to Article

The Adolescent Paradox: Examining the Interplay of Approach and Avoidance Motivations in Adolescent-Onset Anxiety

1. Introduction

Adolescence represents a period of heightened vulnerability to anxiety, with over 31% of US adolescents experiencing anxiety symptoms (Lee et al., 2006; Merikangas et al., 2010). This heightened anxiety is frequently linked to behavioral avoidance (Galván & Peris, 2014; Reniers et al., 2016), a pattern also observed in adults (Maner & Schmidt, 2006). However, this risk-averse phenotype seemingly contradicts the increased risk-taking and exploration characteristic of this developmental stage (Casey et al., 2008). These behaviors, observed across species (Brenhouse & Andersen, 2011; Steinberg, 2008) and cultures (Duell et al., 2018), are crucial for healthy development.

This paper explores the seemingly contrasting phenotypes of adolescence: heightened anxiety with avoidance and inhibition co-existing with increased risk-taking and approach behaviors. We review existing research on the neural correlates of anxiety and risk-taking, aiming to elucidate the mechanisms underpinning anxiety in youth, particularly when such symptoms appear at odds with typical development. We highlight the adaptive function of adolescent risk-taking in fostering independence, learning, and goal-directed behavior (Casey et al., 2008; Spear, 2000), all of which are potentially hindered by anxiety and behavioral avoidance.

We propose that studying adolescent-onset anxiety necessitates considering the concurrent development of approach and avoidance systems and their influence on typical adolescent behaviors, particularly risk-taking. This represents a departure from current research, which often examines these constructs independently, especially within the context of anxiety. Longitudinal studies tracking the interactions and regulation of approach and avoidance motivations across typical and atypical development are critical for a nuanced understanding of the heterogeneity in adolescent anxiety. Such research is essential for identifying vulnerable adolescents and developing effective interventions.

2. The Development of Anxiety

2.1. Background

Anxiety, an evolutionarily adaptive response to environmental stressors (e.g., potential threats), triggers behavioral avoidance rooted in fear to promote safety (Beesdo et al., 2009). While adaptive in early development (Shechner et al., 2012), persistent avoidance can prevent fear extinction, becoming reinforced and habitual (LeDoux et al., 2017). This can lead to functional impairments and increased vulnerability to anxiety (Arnaudova et al., 2017), particularly concerning during adolescence when risk-taking and social interaction become increasingly important for future independence (Casey et al., 2008).

Early adolescence marks the average age of onset for most anxiety disorders (Kessler et al., 2007). Over 31% of US adolescents meet clinical thresholds for an anxiety disorder (Merikangas et al., 2010), with countless others experiencing subclinical symptoms (Beesdo et al., 2009; Siegel & Dickstein, 2011), which are nonetheless linked to negative outcomes like depression, addiction, educational underachievement, and suicidality (Chiu et al., 2016; Kendall et al., 2018; Siegel & Dickstein, 2011; Woodward & Fergusson, 2001). Despite a recent surge in diagnoses (Child Mind Institute, 2018), most anxiety disorders in youth remain undetected and untreated (Benjamin et al., 1990; Child Mind Institute, 2018; Green et al., 2019; Merikangas et al., 2010; Siegel & Dickstein, 2011). Youth often exhibit behavioral and somatic manifestations of anxiety rather than cognitive endorsement of symptoms (e.g., stomach aches; Siegel & Dickstein, 2011). These ambiguous symptoms can be easily missed, especially as routine medical visits decline after childhood (Siegel & Dickstein, 2011). Consequently, youth (ages 12-17) with anxiety are more likely to have unmet mental health needs compared to their non-anxious peers (Green et al., 2019).

Early attentional biases towards threat, often present from infancy, can serve as a predictor of later anxiety (Shechner et al., 2012). Specifically, childhood behavioral inhibition (BI), characterized by fear, wariness, and avoidance of unfamiliar stimuli (Fox et al., 2005), significantly increases the risk of developing anxiety disorders in adolescence (Chronis-Tuscano et al., 2009; Essex et al., 2010; Schwartz et al., 1999). However, it's crucial to acknowledge that not all individuals with BI develop anxiety (Henderson et al., 2015), highlighting the need for research on risk and resilience factors.

Anxiety is believed to impact neural functioning throughout development by modulating attentional processes, specifically by biasing attention towards threatening stimuli. Neuroimaging studies, in both clinical and non-clinical samples, provide evidence for atypical functioning within the "salience network," encompassing the amygdala and prefrontal cortex (PFC), which are critical for regulating attention and threat response (for a comprehensive review, see Blackford & Pine, 2012). However, anxiety's impact extends beyond threat processing; studies also show altered reward processing and atypical functioning in reward-related regions like the striatum in anxious and at-risk youth (Guyer et al., 2006; Lahat et al., 2018). Therefore, a closer examination of the simultaneous development of threat and reward processing networks in at-risk youth is necessary to understand the transition from normative to clinical anxiety.

2.2. Puberty and the Adolescent Brain

The transition to adolescence presents a heightened risk for anxiety development. The onset of puberty initiates an overproduction of axons and synapses throughout the brain, followed by a period of pruning (Crews et al., 2007). During this time, subcortical regions—including the ventral striatum (VS) and amygdala, involved in reward and threat processing respectively—become hyperactive, increasing sensitivity to positive feedback (Galván, 2013). Simultaneously, the PFC, essential for regulatory control, remains underdeveloped (Casey et al., 2008). This asynchronous development is thought to contribute to both the drive for exploration and risk-taking, as well as the vulnerability to negative outcomes observed in adolescence (Casey & Jones, 2010; Galvan et al., 2006).

The Triadic Model provides a framework for understanding adolescent motivated behavior. This model posits that three neural systems – approach (striatum), avoidance (amygdala), and regulatory (PFC) – interact to shape responses to positive and aversive cues (Ernst et al., 2009). It suggests that while adolescents show heightened striatal response to rewards and amygdala response to threats, regulatory systems tend to bias behavior towards approach over avoidance when these motivations conflict (Ernst et al., 2009). This model holds significant promise for studying adolescent-onset anxiety, particularly given the reciprocal roles of the striatum and amygdala in decision-making. The heightened excitability of both reward and threat systems during adolescence adds complexity to the observed behavioral patterns.

Historically, research on VS function during adolescence has primarily focused on its role in reward processing. The dopamine (DA) system, crucial for coordinating neural activity, undergoes significant changes within the adolescent striatum (Ernst et al., 2009; Galvan, 2010). Elevated dopamine levels and greater dopaminergic response to reward in the VS are associated with increased sensation-seeking, including risk-taking (Derringer et al., 2010; Riccardi et al., 2006; Zuckerman, 1985). Moreover, adolescents show greater VS activity in response to rewards compared to children or adults (Galvan, 2010).

Recently, the striatum's role in fear processing and anxiety has become increasingly evident. The striatum's sensitization coincides with the developmental period when anxiety symptoms often first manifest. Additionally, the striatum's interconnectivity with the amygdala, hippocampus, and ventromedial PFC—all key regions implicated in adolescent anxiety—highlights its involvement in motivation, prediction error, and attention (Lago et al., 2017). Pre-clinical studies demonstrate that the VS (e.g., nucleus accumbens; NAcc) is essential for modulating fear responses; adult rats with NAcc lesions exhibited specific impairments in uncertainty-safety discrimination, a process disrupted in clinical anxiety (Ray et al., 2020). While further research is needed to determine if this finding extends to juvenile rats, human studies also link the striatum to anxiety. Anxious youth show greater striatal response to low-value compared to high-value outcomes, potentially reflecting the perceived level of risk (Benson et al., 2014). Additionally, intolerance of uncertainty, a hallmark of anxiety (Dekkers et al., 2017; Osmanağaoğlu et al., 2018), has been positively associated with striatal volume (Kim et al., 2017).

Altered striatal function is also evident in at-risk youth. For instance, behaviorally inhibited adolescents who show increased amygdala activity to threat, also exhibit increased striatal activity to reward (Guyer et al., 2006; Lahat et al., 2018). Similarly, early life adversity has been linked to altered responses to both positive and aversive cues across species (Nelson et al., 2009), impacting both amygdala and striatal development. This, in turn, influences learning and mental health trajectories (Fareri & Tottenham, 2016), highlighting the importance of investigating both regions in the context of anxiety.

Importantly, the striatum receives direct input from the amygdala (Haber & Behrens, 2014), allowing it to translate emotional signals into value-based actions (e.g., approach or avoidance; Fareri & Tottenham, 2016). Disruptions in this communication, crucial for affective development, are observed in anxiety; behaviorally inhibited individuals show reduced amygdala-striatal resting-state connectivity (Roy et al., 2014). Furthermore, animal models highlight the importance of this pathway for motivated behavior, showing that amygdala-NAcc communication is essential for active avoidance in rats (Ramirez et al., 2015). While studies on risk-taking often focus on the VS and PFC, it is critical to consider how reward processing interacts with the threat reactivity of the adolescent amygdala. Conversely, when investigating the heightened anxiety in adolescence, often attributed to the contrasting developmental trajectories of the amygdala and PFC, the role of the VS and its interplay with the amygdala in influencing adolescent decision-making should not be overlooked.

2.3. Risk Taking and Anxiety

While atypical approach and avoidance behaviors have been linked to maladaptive risk-taking (e.g., substance abuse; Casey & Jones, 2010) and affective disorders like anxiety (Arnaudova et al., 2017), there is a lack of research specifically investigating risk-taking in anxious adolescents. Additionally, existing research predominantly focuses on "dangerous" risk-taking (e.g., substance abuse), neglecting the potential benefits of adaptive risk-taking during adolescence (Duell & Steinberg, 2019). Although anxiety is often characterized by risk aversion (Sonuga-Barke et al., 2016), the heterogeneity of the disorder and its interaction with adolescent development adds layers of complexity.

While some studies indicate that anxious adolescents, due to their risk aversion, may be less likely to engage in substance abuse (Malmberg et al., 2010), others report an increased risk in this population (Child Mind Institute, 2018; Kilgus & Pumariega, 2009; Low et al., 2008). These inconsistencies may be partially attributed to sex and gender differences; female adolescents tend to show stronger associations between anxiety and substance use compared to males (Cruz et al., 2017; Wu et al., 2010).

Furthermore, research suggests the existence of anxiety subtypes with distinct behavioral profiles. For example, one study identified two subtypes of social anxiety: one characterized by the classic behavioral inhibition and risk avoidance, and the other, termed "approach-motivated," characterized by impulsivity, reward sensitivity, risk-taking, and substance abuse (Nicholls et al., 2014). Another study, investigating a genetic moderator of loss aversion and impulsivity in anxious adolescents, found that a specific gene variant was associated with low loss aversion and high impulsivity, suggesting a genetic predisposition for risk-taking in anxious youth (Ernst et al., 2014).

Understanding these different behavioral profiles of anxiety is paramount, especially considering the implications for the juvenile justice system. Anxiety and depressive symptoms are prevalent in juvenile offenders (Cauffman, 2004) and may contribute to offending behaviors (Copeland et al., 2007; Hoeve et al., 2013). However, mental health needs within this population often remain unaddressed (Zajac et al., 2015). These findings highlight the need to consider risk-relevant traits, such as impulsivity and reward sensitivity, in addition to threat sensitivity when studying adolescent anxiety.

2.4. Threat vs. Thrill

Risky decision-making does not always stem from the pursuit of a tangible reward. Instead, the presence of potential threat can activate reward circuitry, eliciting rewarding sensations (Spielberg et al., 2014). This phenomenon, observed across ages, suggests that the potential for threat, whether experienced on a roller coaster or by forgoing a helmet, can be perceived as rewarding. For instance, a program called "Adrenaline Instead of Amphetamine" found that engaging in activities like skydiving (a legal thrill) could effectively treat stimulant addiction in adults (Makarowski et al., 2016). This suggests that the adrenaline rush from potential threat can mimic the rewarding effects of drugs. While this therapy has only been tested in adults, future research could explore its application in younger populations.

Due to the asynchronous development of threat, reward, and regulatory systems, the experience of thrill associated with risky situations might be uniquely amplified during adolescence (Dahl, 2004). This sensation plays a role in many adolescent risk-taking behaviors, including romantic pursuits and sexual exploration. Social interactions, often described as inducing "butterflies in the stomach," illustrate the intertwining of reward and anxiety during this period. To navigate these potentially anxiety-provoking experiences, it would be advantageous for the adolescent brain to possess a nuanced perception of threat, one that can simultaneously process danger as both frightening and rewarding. Research supports this notion, showing that adolescents, compared to children and adults, exhibit greater tolerance for uncertainty during risky decision-making (Van Den Bos & Hertwig, 2017) and are more willing to take risks when the potential consequences are ambiguous (Tymula et al., 2012).

While risk-taking is associated with tolerance of uncertainty (Blankenstein et al., 2016), anxiety is often characterized by an intolerance of it (Dekkers et al., 2017; Osmanağaoğlu et al., 2018). A study on unmedicated anxious adults found that their risk avoidance was driven by risk sensitivity (intolerance of uncertain outcomes) rather than an increased sensitivity to potential loss (Charpentier et al., 2017). This suggests that for anxious adolescents, the very element of uncertainty that others find thrilling might be perceived as threatening. Future research should investigate how individual differences in tolerance of uncertainty influence anxiety trajectories.

To investigate the potential rewarding aspect of threat during puberty, Spielberg et al. (2014) found that increased amygdala response to threat over time was associated with higher sensation-seeking and lower anxiety, but only in individuals who also showed increased VS response to threat. Another study, examining learning under evaluation threat, found that striatal activity during learning tracked performance in adolescents, such that greater activity was associated with better learning, a pattern not observed in adults (Depasque & Galván, 2019). This finding adds nuance to previous research showing that adolescents with a history of BI exhibit increased striatal response during decision-making when outcomes are contingent on their actions (Bar-Haim et al., 2009). It remains unclear how anxiety might influence striatal response to evaluation threat and whether this response facilitates or hinders learning.

Further research on amygdala-striatal interactions during adolescence, and their influence on behavior and mental health, is critical for developing targeted interventions. It is plausible that amygdala reactivity, in conjunction with VS activity, can promote approach over avoidance behaviors. Encouraging positive risk-taking by framing threat as potentially rewarding could be a valuable preventative strategy for anxiety. Previous studies suggest that reward-based training can effectively reduce anxiety and, importantly, carries a lower risk of exacerbating anxiety compared to threat-focused treatments (Dandeneau & Baldwin, 2009). If the hyperactive adolescent striatum drives engagement and perseverance in learning under threat, perhaps it collaborates with the amygdala to reinterpret threat and encourage learning during risky decision-making. Therefore, a comprehensive examination of the development of both reward and threat systems and their contributions to risk-taking and learning is crucial.

3. Measuring Meaningful Change

3.1. A Need for Longitudinal Studies

While research has identified neural correlates of anxiety in youth, we lack an understanding of the transition from normative to clinical anxiety from a neurobiological perspective. Cross-sectional studies provide snapshots of neural development across different individuals at various ages. However, to examine the dynamic interplay between fronto-amygdala-striatal circuits during adolescence and their influence on anxiety trajectories, longitudinal studies that track individuals across the anxiety continuum are essential.

Longitudinal studies also allow researchers to investigate the developmental interplay of multiple factors associated with anxiety. For instance, sleep difficulties, prevalent during adolescence, often precede anxiety symptoms, predict worsening anxiety, and significantly impact mental health, particularly in early adolescence (McMakin & Alfano, 2015). Additionally, poor sleep is associated with both increased anxiety (Kelly & El-Sheikh, 2014) and risk-taking behaviors (Baker et al., 2020; Telzer et al., 2013). Investigating the relationship between sleep difficulties and anxiety as youth enter adolescence can provide valuable insights into anxiety development and potential interventions.

3.2. Neuroimaging Methods

3.2.1. Dynamic Causal Modeling (DCM)

Current knowledge about the neural underpinnings of anxiety primarily stems from correlational findings (e.g., greater amygdala activity correlating with anxiety severity). However, this limits our ability to understand how these regions causally influence each other and impact behavior. It remains unclear whether anxiety is driven by an overactive amygdala, excessive PFC regulation, or the competing influences of the amygdala and VS.

Future studies can benefit from incorporating methods like Dynamic Causal Modeling (DCM). DCM enables inferences about causal relationships between brain regions (e.g., amygdala, PFC, VS) by measuring effective connectivity. This allows researchers to estimate how neuronal changes in one region influence activity in another. This method is particularly relevant for developmental samples as it can capture the complex dynamics of interacting brain networks that undergo continuous remodeling (Goldenberg & Galván, 2015). DCM allows researchers to address targeted questions regarding the neural processes underlying adolescent decision-making.

3.2.2. Reliability

Despite the promise of longitudinal neuroimaging, it is crucial to consider the test-retest reliability of these methods in developmental and at-risk populations (Herting et al., 2018). Reliability is essential to differentiate true developmental changes from noise or artifacts. Different imaging modalities have varying levels of reliability. For instance, structural measures like grey and white matter volume, and diffusion tensor imaging (DTI) show high reliability across scans in youth (Drobinin et al., 2020). In contrast, task-based fMRI exhibits good reliability in some regions (e.g., occipital lobe) but lower reliability in subcortical areas like the amygdala and VS (Vetter et al., 2017). The chosen analysis method can also influence reliability. DCM, in addition to its analytic strengths, shows relatively high test-retest reliability (Frässle et al., 2015; Schuyler et al., 2010).

To improve reliability in developmental samples, researchers can implement strategies such as minimizing head motion during scans (e.g., prioritizing participant comfort and offering breaks), incorporating additional test-retest scans within the protocol with minimal time between measurements, and utilizing multimodal imaging approaches (Herting et al., 2018). Combining anatomical and functional connectivity measures (e.g., DTI and fMRI) has provided valuable insights into the development of brain networks in children (Supekar et al., 2010). Similarly, multimodal neuroimaging data have been shown to improve the accuracy of brain-based age prediction (Liem et al., 2017). Employing a multimodal approach offers a richer and more comprehensive understanding of the developing brain and mitigates the risk of spurious findings.

Finally, recruiting large, diverse samples is crucial for enhancing replicability and generalizability. Smaller samples increase the likelihood of spurious or non-generalizable findings. Even samples exceeding 100 participants may not guarantee perfect reliability (Turner et al., 2018). To comprehensively examine individual differences in anxiety risk, adequate sampling from a diverse population across the anxiety continuum is essential.

4. Conclusion

Anxiety, a prevalent concern among youth, can significantly impair functioning and often worsens in severity after adolescence (Beesdo et al., 2009; Bittner et al., 2007; Broeren et al., 2013; Kessler et al., 2007; Merikangas et al., 2010). The neural processes associated with anxiety seemingly contradict the increased risk-taking and exploration typical of adolescence (Casey et al., 2008). Further research is needed to clarify how the simultaneous development of fronto-amygdala and fronto-striatal circuits impacts attention and anxiety during this period. For instance, do anxious youth who exhibit concurrent amygdala and VS activity during risk-taking engage in more risky behaviors, potentially reflecting a more normative developmental trajectory? Addressing these questions is crucial for understanding how anxiety manifests in adolescence and identifying optimal treatment strategies. Prospective longitudinal studies that track approach and avoidance motivations, risk-taking, and mental health throughout puberty are necessary to understand risk and resilience factors and, ultimately, to provide effective support for adolescents struggling with anxiety.

Link to Article

1. Introduction

Anxiety is a common experience during adolescence. In fact, over 31% of teenagers in the US report feeling anxious (Lee et al., 2006; Merikangas et al., 2010). This anxiety can lead young people to avoid situations that make them uncomfortable (Galván & Peris, 2014; Reniers et al., 2016). Interestingly, this happens at the same time that teenagers are naturally driven to explore new things and take more risks (Casey et al., 2008) – behaviors that are actually important for healthy development and seen across different species and cultures (Brenhouse & Andersen, 2011; Duell et al., 2018; Steinberg, 2008).

So why do we see these seemingly opposite behaviors in adolescence – an increase in anxiety that makes teens want to avoid things, and an increase in risk-taking that makes them want to try new things? This paper examines the research on the brain's role in anxiety and risk-taking to better understand why anxiety emerges during this time of development. We'll discuss how risk-taking during adolescence is actually important for learning and becoming independent (Casey et al., 2008; Spear, 2000) – things that anxiety can get in the way of.

We argue that studying anxiety in teenagers means looking at how their brains handle both approaching things they want and avoiding things they fear. This is different from most research, which looks at these two systems separately, especially when studying anxiety. We need more research that follows young people over time to see how these systems interact and develop, both in those who experience anxiety and those who don't. This will help us better understand why anxiety affects some teenagers more than others, identify those who are vulnerable, and develop effective ways to help them.

2. The Development of Anxiety

2.1. Background

Experiencing anxiety is normal. In fact, it's a natural response to stress and potential danger that helps us stay safe. When we feel anxious, we avoid things that might be harmful (Beesdo et al., 2009). This avoidance is helpful when we're young (Shechner et al., 2012), but consistently avoiding things can become a problem. It can prevent us from learning that something isn't actually dangerous and make us even more anxious (Arnaudova et al., 2017; LeDoux et al., 2017). This is especially concerning during adolescence, as teens are starting to engage in more risk-taking and social interaction, both of which are essential for becoming independent adults (Casey et al., 2008).

Most anxiety disorders emerge during adolescence (Kessler et al., 2007), with over 31% of teenagers in the US showing signs of an anxiety disorder (Merikangas et al., 2010). Many more experience typical anxiety (Beesdo et al., 2009; Siegel & Dickstein, 2011), which can still have negative consequences like depression, substance abuse, problems in school, and even suicidal thoughts (Chiu et al., 2016; Kendall et al., 2018; Siegel & Dickstein, 2011; Woodward & Fergusson, 2001). Worryingly, even though diagnoses of anxiety disorders in young people have increased by 17% in the last decade (Child Mind Institute, 2018), most cases go undiagnosed and untreated (Benjamin et al., 1990; Child Mind Institute, 2018; Green et al., 2019; Merikangas et al., 2010; Siegel & Dickstein, 2011). Instead of talking about their anxiety, young people often show physical symptoms like stomachaches (Siegel & Dickstein, 2011). Since teenagers don't see the doctor as often as younger children, these symptoms can be missed (Siegel & Dickstein, 2011).

Even before obvious signs appear, young children might show attention biases that can predict later anxiety. These biases are noticeable even in infancy (Shechner et al., 2012). One strong predictor of anxiety in teenagers is a pattern of behavior called behavioral inhibition (BI) in childhood. Kids with BI are fearful and avoid new people or situations (Fox et al., 2005; Broeren et al., 2013; Domschke & Maron, 2013; Henderson et al., 2015). They are four times more likely to develop anxiety disorders in adolescence (Chronis-Tuscano et al., 2009; Essex et al., 2010; Schwartz et al., 1999). However, not everyone with BI becomes anxious (Henderson et al., 2015). Therefore, studying both what makes these children vulnerable and what makes them resilient is key to understanding and preventing anxiety in adolescence.

Anxiety seems to affect how the brain pays attention to threats. Brain imaging studies show that both clinically anxious and non-clinically anxious individuals show unusual activity in the brain's "salience network." This network, which includes the amygdala (involved in processing threats) and the prefrontal cortex (PFC, involved in regulating responses), helps us control our attention and reactions to potential danger (Blackford & Pine, 2012). But anxiety doesn’t just affect how our brains process threats; it also seems to impact how we process rewards. Studies in anxious and at-risk youth have found unusual activity in reward-related areas like the striatum (Guyer et al., 2006; Lahat et al., 2018). To understand how anxiety develops, we need to study how the brain develops the ability to process both threats and rewards in at-risk youth.

2.2. Puberty and the Adolescent Brain

The transition from childhood to adolescence is a time of significant change in the brain, making it a critical period for the development of anxiety. Puberty triggers a surge in the growth of connections in the brain, followed by a period of "pruning" where unnecessary connections are eliminated (Crews et al., 2007). During this time, areas like the ventral striatum (VS) and amygdala, which are involved in processing rewards and threats, become highly reactive, increasing desire for positive feedback (Galván, 2013). Meanwhile, the PFC, responsible for regulating these responses, is still developing (Casey et al., 2008). This difference in development between these systems might explain why adolescents are driven to explore and take risks, but are also vulnerable to negative outcomes (Casey & Jones, 2010; Galvan et al., 2006).

One model that helps explain how motivation works in the adolescent brain is the Triadic Model. This model proposes that three systems - approach, avoidance, and regulation - interact to shape how teenagers respond to positive and negative situations (Ernst et al., 2009). While adolescents have heightened responses to both rewards (in the VS) and threats (in the amygdala), their regulatory systems tend to favor approaching rewarding things, even when risks are involved (Ernst et al., 2009). This model is helpful for understanding adolescent anxiety because it highlights the interplay between the VS and amygdala in decision-making. The fact that both reward and threat systems are still developing and are more easily activated during adolescence adds another layer of complexity to understanding their behavior.

Historically, research on the VS during adolescence has mainly focused on its role in reward. This area is strongly influenced by the brain's dopamine (DA) system, which undergoes changes during adolescence (Ernst et al., 2009; Galvan, 2010). Higher levels of dopamine and stronger responses to rewards in the VS have been linked to a greater tendency to seek out new and exciting experiences (Derringer et al., 2010; Riccardi et al., 2006; Zuckerman, 1985). Additionally, research shows that adolescents' VS are more active than children's or adults' when they receive rewards (Galvan, 2010).

More recently, researchers have started to investigate the role of the striatum in fear and anxiety. Interestingly, the striatum becomes more sensitive around the same time that anxiety often first appears. Furthermore, the striatum has strong connections with other key brain areas involved in adolescent anxiety – the amygdala, hippocampus, and ventromedial PFC. The striatum is known to play a major role in motivation, learning, and attention (Lago et al., 2017). Studies in rats have shown that the nucleus accumbens (NAcc), a part of the VS, is important for distinguishing between safe and uncertain situations - a skill that is impaired in people with anxiety (Ray et al., 2020). While more research is needed to confirm if this is also true in young rats, studies in humans show a link between striatal activity and anxiety. Anxious youth show a stronger response in the striatum to less valuable rewards (potentially due to the perceived risk associated with them) and increased VS activity when anticipating feedback (Benson et al., 2014). Moreover, intolerance of uncertainty, a hallmark of anxiety (Dekkers et al., 2017; Osmanağaoğlu et al., 2018), has been linked to larger striatal volume (Kim et al., 2017).

Altered striatal function has also been observed in at-risk youth. For instance, behaviorally inhibited adolescents, who typically show heightened amygdala activity in response to threats, also exhibit increased striatal activity during reward processing (Guyer et al., 2006; Lahat et al., 2018). Similarly, experiencing adversity early in life has been linked to altered responses to both positive and negative situations across species (Nelson et al., 2009), as well as changes in the development of both the amygdala and striatum (Fareri & Tottenham, 2016). These changes can influence learning and mental health, underscoring the need to study both regions in the context of anxiety.

The amygdala sends signals to the striatum (Haber & Behrens, 2014), allowing it to translate emotions into actions (e.g., approach or avoid; Fareri & Tottenham, 2016). This communication is crucial for healthy emotional development and might be disrupted in anxiety. For example, people with behavioral inhibition show weaker resting-state connectivity between the amygdala and striatum (Roy et al., 2014). Additionally, animal studies suggest that communication between these areas is essential for motivated behavior. For instance, rats need proper signaling between the amygdala and NAcc to effectively avoid danger (Ramirez et al., 2015).

While studies often focus on the VS and PFC when investigating risk-taking, it's essential to consider how the amygdala, with its heightened sensitivity to threat during adolescence, interacts with reward-related processes to influence decision-making. Conversely, while the typical explanation for increased anxiety in adolescence centers on the contrasting developmental trajectories of the amygdala and PFC, it's crucial to understand how the VS interacts with the amygdala to impact decisions.

2.3. Risk Taking and Anxiety

Although problems with approaching desired things and avoiding feared things have been linked to both unhealthy risk-taking (like substance abuse; Casey & Jones, 2010) and mental health issues like anxiety (Arnaudova et al., 2017), there's limited research on risk-taking specifically in anxious adolescents. Existing research mainly focuses on risky behaviors with clear negative consequences (e.g., substance abuse) in anxiety, with less emphasis on the potential benefits of healthy risk-taking for development (Duell & Steinberg, 2019). While anxiety is often characterized by avoiding risk (Sonuga-Barke et al., 2016), the varying ways anxiety presents and its interaction with typical adolescent development make this a complex issue.

While some studies indicate that anxious adolescents might be less likely to abuse substances due to their risk aversion (Malmberg et al., 2010), others suggest they might actually be at a higher risk (Child Mind Institute, 2018; Kilgus & Pumariega, 2009; Low et al., 2008). Sex and gender differences might contribute to these differences in behavior. For example, studies show a stronger link between anxiety and drug and alcohol use in teenage girls than boys (Cruz et al., 2017; Wu et al., 2010).

Research also points to different subtypes of anxiety with distinct behavioral patterns. One study identified two types of social anxiety: one characterized by the typical pattern of behavioral inhibition and risk avoidance, and another – called the "approach-motivated" subtype – characterized by impulsivity, reward sensitivity, risk-taking, and substance abuse (Nicholls et al., 2014). Another study investigated a specific gene variant that influences how sensitive people are to losses and how impulsive they are. In anxious adolescents, high expression of this gene variant was associated with low sensitivity to losses and high impulsivity, suggesting that this gene might make some anxious youth more likely to take risks (Ernst et al., 2014).

Understanding these different behavioral profiles of adolescent anxiety is particularly important when considering the implications for the juvenile justice system. Anxious and depressed teenagers are over-represented in this system (Cauffman, 2004), and these mental health issues might contribute to their criminal behavior (Copeland et al., 2007; Hoeve et al., 2013). Unfortunately, their mental health needs often go unmet (Zajac et al., 2015). These findings highlight the need to consider factors like impulse control and reward sensitivity (in addition to threat sensitivity) in studies on adolescent anxiety.

2.4. Threat vs. Thrill

Risky decisions aren’t always about potential rewards. The presence of potential threat itself can activate the brain’s reward system and trigger feelings of excitement (Spielberg et al., 2014). This is true for people of all ages, whether it’s riding a rollercoaster, skydiving, or riding a bike without a helmet. For example, a program called “Adrenaline Instead of Amphetamine” found that men addicted to stimulating drugs like amphetamine could reduce their drug use by engaging in activities like skydiving (Makarowski et al., 2016). The adrenaline rush from these activities seemed to mimic the rewarding feelings of the drugs. While this therapy has only been tested in adults, it might also be effective for younger populations.

Because the systems responsible for processing threats, rewards, and regulating our responses develop at different rates, experiencing danger might be uniquely thrilling during adolescence (Dahl, 2004). The feeling of thrill is a part of many adolescent risk-taking behaviors, including romantic relationships and sexual exploration. As the phrase “butterflies in the stomach” suggests, social interactions during adolescence can be both exciting and terrifying. For adolescents to learn from these new and potentially scary experiences, their brains need to be able to experience danger as both frightening and exciting. This is supported by research showing that teenagers are more comfortable with uncertainty when making risky decisions than both children and adults (Van Den Bos & Hertwig, 2017) and are more willing to take risks when the risks are unclear (Tymula et al., 2012).

Risk-taking has been linked to a tolerance of uncertainty (Blankenstein et al., 2016), while anxiety is often associated with an intolerance of it (Dekkers et al., 2017; Osmanağaoğlu et al., 2018). A study of adults with anxiety found that their avoidance of risk was driven by their aversion to uncertain outcomes, not by a heightened sensitivity to potential losses (Charpentier et al., 2017). This suggests that what makes risk exciting for some adolescents – the uncertainty of the outcome – might be perceived as threatening by those with anxiety. Further research on risk-taking in anxious youth is needed to understand how changes in their tolerance of uncertainty might influence the development of anxiety.

To investigate whether threat becomes uniquely rewarding during puberty, Spielberg and colleagues (2014) found that adolescents who showed increases in both amygdala activity in response to threat and VS activity in response to threat over time also reported higher levels of sensation seeking and lower levels of anxiety. Another study found that when adolescents were learning under pressure, their striatal activity predicted how well they learned (Depasque & Galván, 2019). This pattern, where greater striatal activity was linked to better learning under pressure, was not observed in adults. These findings add to previous research showing that adolescents with a history of behavioral inhibition showed increased striatal activity when their decisions influenced the outcome (Bar-Haim et al., 2009). It raises the question of how anxiety might impact the striatum’s response to pressure and whether this brain response helps or hinders learning.

To develop effective interventions for anxiety, we need to understand how the amygdala and striatum interact to influence behavior and mental health throughout adolescence. Perhaps, in conjunction with VS activity, amygdala reactivity could promote approaching desired experiences rather than avoiding feared ones. It’s possible that by linking threat to reward, we can encourage healthy risk-taking and prevent anxiety in adolescence. Some research suggests that reward-based training can effectively reduce anxiety and, importantly, carries a lower risk of making anxiety worse compared to treatments focused on threats (Dandeneau & Baldwin, 2009). If the hyperactive striatum in adolescence drives teenagers to learn, even under pressure, perhaps it works with the amygdala to reframe threats as opportunities for learning during risky decision-making. Therefore, it’s essential to study how both reward and threat systems develop together and how they contribute to risk-taking and learning.

3. Measuring Meaningful Change

3.1. A Need for Longitudinal Studies

While we have learned a lot about the brain activity associated with anxiety in youth, we still don’t fully understand how the brain changes as typical anxiety develops into a clinical disorder during adolescence. Cross-sectional studies, which provide snapshots of brain development in different individuals at different ages, have helped identify brain regions involved in anxiety. However, to understand how these regions interact and change over time, and how these changes relate to the development of anxiety, we need longitudinal studies that follow the same individuals over time.

Longitudinal studies also allow us to track other developmental processes that occur alongside anxiety. For example, sleep problems, common during adolescence, can be both a precursor and a predictor of anxiety, especially in early adolescence (McMakin & Alfano, 2015). Poor sleep is also linked to both increased anxiety (Kelly & El-Sheikh, 2014) and more risk-taking behavior (Baker et al., 2020; Telzer et al., 2013). By tracking the relationship between sleep problems and anxiety as young people enter adolescence, we can gain valuable insights into the development of anxiety and potential ways to intervene.

3.2. Neuroimaging Methods

3.2.1. Dynamic Causal Modeling (DCM)

Most of what we know about how the brain develops and functions in anxious youth comes from studies that show correlations between brain activity and behavior. For example, these studies might show that greater activity in the amygdala is correlated with more severe anxiety, or that anxious youth have reduced PFC activity when looking at emotional images. However, these studies don’t tell us how these brain regions influence each other. Does anxiety result from an overactive amygdala, an overworked PFC, or competing influences between the amygdala and VS?

Future studies could benefit from techniques like Dynamic Causal Modeling (DCM), which allows us to investigate how activity in one brain region influences activity in another. This is done by measuring “effective connectivity” between regions. This method is particularly promising for studying development because it can capture the complex interactions within and between brain networks as they change over time (Goldenberg & Galván, 2015). Using DCM, researchers can start to untangle the chain of events that occur in the brain during decision-making.

3.2.2. Reliability

While longitudinal neuroimaging studies hold great promise for understanding developmental changes, it’s essential to consider the reliability of these methods, especially in young and at-risk populations. Reliability refers to how consistent the results of a measurement tool are over time (Khoo et al., 2007). In neuroimaging, this means that if we scan someone’s brain twice, we should get similar results (Herting et al., 2018). Without establishing reliability, it’s difficult to know whether observed changes are due to actual developmental changes or simply random variations in the data. Different imaging techniques have different levels of reliability. For example, structural measures of brain development, such as grey and white matter volume, tend to be very reliable (Drobinin et al., 2020). Task-based fMRI, where brain activity is measured while someone is performing a task, shows good reliability in some areas (e.g., the occipital lobe) but lower reliability in areas like the amygdala and VS (Vetter et al., 2017). The analysis method used can also impact reliability. In addition to its analytical advantages, DCM has demonstrated relatively good reliability across scanning sessions (Frässle et al., 2015; Schuyler et al., 2010).

There are several things researchers can do to improve reliability in developmental samples. These include minimizing movement in the scanner by making participants comfortable and allowing for breaks, scheduling repeat scans close together in time, and using multiple types of imaging techniques (Herting et al., 2018). For example, combining structural imaging (e.g., DTI) with functional imaging (e.g., fMRI) has provided valuable insights into how brain networks develop in children (Supekar et al., 2010). Researchers have also found that they can more accurately predict someone’s age based on their brain activity when using data from multiple imaging modalities (Liem et al., 2017). In general, using multiple types of imaging provides a more detailed picture of the developing brain and can reduce the likelihood of inaccurate findings.

Finally, a crucial strategy for improving the reliability and generalizability of research findings is to recruit large and diverse groups of participants. Smaller sample sizes increase the risk of inaccurate or misleading findings (Turner et al., 2018). To fully understand the individual differences in how anxiety develops, we need to study a large and diverse group of young people who fall across the entire spectrum of anxiety.

4. Conclusion

Anxiety is a common experience for many young people, can significantly impact their lives, and often worsens as they move through adolescence (Beesdo et al., 2009; Bittner et al., 2007; Broeren et al., 2013; Kessler et al., 2007; Merikangas et al., 2010). The way the brain processes threats in anxiety appears to directly clash with typical adolescent behaviors like exploring and taking risks (Casey et al., 2008). This raises important questions: How do the developing brain systems responsible for approaching desired things and avoiding feared things, along with the brain regions responsible for regulating these impulses, interact and influence attention and anxiety in adolescents? Do anxious teenagers who show simultaneous activity in the amygdala and VS during risk-taking engage in more risky behavior, potentially achieving a more typical developmental trajectory? Answering these questions about why both sensation-seeking and anxiety increase during adolescence is crucial for understanding how anxiety develops and for identifying the best time to intervene and the most effective ways to do so. To understand what makes some adolescents vulnerable and others resilient, we need to conduct longitudinal studies that follow at-risk youth through puberty and track their motivations to approach and avoid, their risk-taking behavior, and their mental health. These studies are essential for improving the lives of young people struggling with anxiety.

Link to Article

1. Introduction

Lots of teens experience anxiety – more than 30%. Anxiety can make a person want to avoid things that make them nervous (Galván & Peris, 2014; Reniers et al., 2016; Maner & Schmidt, 2006). But here's the thing: being a teenager is all about trying new things and taking risks (Casey et al., 2008). It's how we learn and grow (Brenhouse & Andersen, 2011; Steinberg, 2008; Duell et al., 2018).

So how can teenagers be both anxious and risk-takers? This article explores what's happening in the brain during adolescence and how that relates to anxiety. We'll see that risk-taking can actually be a good thing and that anxiety can get in the way of important teenage experiences.

Finally, we'll discuss why it's important to study anxiety and risk-taking together, especially in teenagers. This can help us understand why some teens struggle with anxiety and how to better support them.

2. The Development of Anxiety

2.1. Background

Everyone feels anxious sometimes – it's a normal emotion that helps keep us safe. When we sense danger, anxiety makes us want to avoid it (Beesdo et al., 2009). This is helpful when we're young (Shechner et al., 2012). But, constantly avoiding things that make us anxious can backfire. We miss out on chances to learn that things aren't so scary after all. This can lead to more anxiety and make it harder to do the things we want and need to do (Arnaudova et al., 2017; LeDoux et al., 2017). This is a big deal during the teenage years when we start to become more independent (Casey et al., 2008).

Many anxiety disorders start during the teenage years (Kessler et al., 2007). Over 30% of teenagers in the U.S. have an anxiety disorder, and many more experience some anxiety symptoms (Merikangas et al., 2010; Beesdo et al., 2009; Siegel & Dickstein, 2011). Anxiety can lead to other problems like depression, substance abuse, trouble in school, and even thoughts of suicide (Chiu et al., 2016; Kendall et al., 2018; Siegel & Dickstein, 2011; Woodward & Fergusson, 2001). Even though anxiety is common, most teenagers with anxiety disorders don't get the help they need (Benjamin et al., 1990; Child Mind Institute, 2018; Green et al., 2019; Merikangas et al., 2010; Siegel & Dickstein, 2011). This is partly because teenagers may not talk about their anxiety directly but instead show physical symptoms like stomachaches (Siegel & Dickstein, 2011).

Before anxiety even shows up, kids might start paying more attention to threats, even as babies (Shechner et al., 2012)! One sign that a teenager might develop anxiety is if they were really shy or afraid of new things as a child (Fox et al., 2005; Broeren et al., 2013; Domschke & Maron, 2013; Henderson et al., 2015). But, not every shy kid becomes an anxious teenager (Henderson et al., 2015). This means it's super important to figure out what makes some kids more resilient than others.

Scientists think anxiety changes how our brains work, particularly a network of brain areas responsible for noticing and responding to threats (Blackford & Pine, 2012). This network includes the amygdala (the "fear center") and the prefrontal cortex (PFC; involved in planning and control). But, anxiety also seems to affect how our brains process rewards. This involves areas like the striatum (Guyer et al., 2006; Lahat et al., 2018). To truly understand how anxiety develops, we need to look at how these brain areas work together.

2.2. Puberty and the Adolescent Brain

The teenage years, especially puberty, are a time of massive change in the brain. Think of it like a huge rewiring project (Crews et al., 2007)! This makes teenagers more sensitive to both rewards and threats (Galván, 2013). The teenage brain is wired to seek out exciting experiences (Casey et al., 2008). But, the part of the brain that helps us control impulses and make good decisions (the PFC) is still under construction (Casey et al., 2008; Casey & Jones, 2010; Galvan et al., 2006). This explains why teenagers are known for both their adventurous spirit and sometimes not-so-great choices.

The Triadic Model helps explain how teenagers make decisions (Ernst et al., 2009). It describes three brain systems:

• Approach: Driven by the striatum, this system makes us want good things (like rewards).

• Avoidance: Driven by the amygdala, this system makes us want to avoid bad things (like threats).

• Regulatory: Driven by the PFC, this system helps us control our impulses and make good decisions.

In teenagers, the approach and avoidance systems are super strong, while the regulatory system is still catching up (Ernst et al., 2009). This explains why teenagers are more likely to go for it, even if it means taking a risk.

The striatum is a key player in motivation and decision-making (Lago et al., 2017). It's highly influenced by dopamine, a chemical messenger in the brain that makes us feel good (Ernst et al., 2009; Galvan, 2010). Teenagers have higher dopamine levels than kids or adults, which is thought to be linked to their increased risk-taking (Derringer et al., 2010; Riccardi et al., 2006; Zuckerman, 1985; Galvan, 2010).

But, the striatum isn't just about rewards – it also plays a role in anxiety. Research shows that teenagers with anxiety may have differences in how their striatum responds to rewards and potential risks (Benson et al., 2014; Kim et al., 2017).

Studies have even shown that shy teenagers have more activity in both the amygdala (when facing threats) and the striatum (when anticipating rewards) compared to their less shy peers (Guyer et al., 2006; Lahat et al., 2018). This suggests that anxiety isn't just about being afraid but also about how we think about rewards.

The amygdala and the striatum are connected, and this connection is important for controlling our emotions and actions (Haber & Behrens, 2014; Fareri & Tottenham, 2016). Problems with this connection might contribute to anxiety. For example, shy people show weaker connections between these areas when their brain is at rest (Roy et al., 2014). Studies in rats have shown that communication between these areas is also crucial for avoiding danger (Ramirez et al., 2015). This means that to understand how anxiety develops, we need to look at how the amygdala and striatum work together.

2.3. Risk-Taking and Anxiety

We tend to think of anxiety and risk-taking as opposites. But, it's more complicated than that, especially in teenagers (Sonuga-Barke et al., 2016). While some studies suggest that anxious teenagers are less likely to use drugs and alcohol (Malmberg et al., 2010), others show they might be at higher risk (Child Mind Institute, 2018; Kilgus & Pumariega, 2009; Low et al., 2008). Gender might play a role too, with anxious girls being more vulnerable to substance abuse than boys (Cruz et al., 2017; Wu et al., 2010).

It's possible that there are different types of anxiety, each with its own behaviors. Some researchers believe there's a type of social anxiety marked by impulsivity, thrill-seeking, and risk-taking, including substance abuse (Nicholls et al., 2014). Additionally, our genes might influence how anxiety and risk-taking interact (Ernst et al., 2014).

Understanding these different profiles is important, especially for teenagers involved in the justice system. Anxiety and depression are common in young offenders and might contribute to criminal behavior (Cauffman, 2004; Copeland et al., 2007; Hoeve et al., 2013). Unfortunately, these mental health needs often go unmet (Zajac et al., 2015). This highlights the need to consider factors like impulsivity and reward sensitivity when we think about anxiety in teenagers.

2.4. Threat vs. Thrill

Here's a surprising thought: sometimes, what we perceive as dangerous can also be exciting and rewarding! Think about rollercoasters or skydiving – these activities are thrilling because they involve an element of risk (Spielberg et al., 2014). Interestingly, some adults addicted to drugs like amphetamines have found success in replacing their addiction with thrilling (but safe) activities like skydiving (Makarowski et al., 2016). The adrenaline rush from these activities seems to mimic the rewarding feelings of drugs. While this type of therapy hasn't been tested in teenagers yet, it's a promising avenue for future research.

For teenagers, the developing brain might experience thrills even more intensely than adults do (Dahl, 2004). This applies to all sorts of risks, from trying out for the school play to going on a first date. These experiences can be both nerve-wracking and exhilarating!

Research suggests that teenagers are more comfortable with uncertainty than children or adults, especially when making risky decisions (Van Den Bos & Hertwig, 2017; Tymula et al., 2012). This means they might be more willing to take a risk if they don't know what will happen. This contrasts with anxiety, which is often linked to a dislike of uncertainty (Dekkers et al., 2017; Osmanağaoğlu et al., 2018).

One study found that adults with anxiety were more sensitive to the possibility of a negative outcome, rather than being overly focused on the loss itself (Charpentier et al., 2017). This means that the uncertainty of a situation – the very thing that can make it exciting for some teenagers – might be what makes it scary for anxious teenagers.

In one study, teenagers who showed increased activity in both the amygdala (fear) and the striatum (reward) when facing threats were also more likely to enjoy taking risks and had fewer anxiety symptoms (Spielberg et al., 2014). Another study found that teenagers who showed increased striatum activity while learning under pressure actually performed better than those who didn't show this pattern (Depasque & Galván, 2019). This suggests that a little bit of pressure might actually be beneficial for teenagers, helping them learn and grow.

These findings highlight the importance of studying how the amygdala and striatum work together during adolescence. It's possible that by reframing threat as a potential reward, we can help teenagers overcome their anxiety and embrace healthy risk-taking. Reward-based training programs show promise in reducing anxiety and may be a safer alternative to therapies that focus on directly confronting fears (Dandeneau & Baldwin, 2009).

3. Measuring Meaningful Change

3.1. A Need for Longitudinal Studies

We've learned a lot about how anxiety looks in the brain, but we still don't fully understand how it develops over time, especially during the turbulent teenage years. To do this, we need longitudinal studies that follow the same group of young people over a period of years. This allows researchers to track how anxiety changes (or doesn't change) and identify factors that might contribute to these changes.

Longitudinal studies can also help us understand the relationship between anxiety and other factors, such as sleep. Sleep problems are common during adolescence and can both contribute to and be made worse by anxiety (McMakin & Alfano, 2015; Kelly & El-Sheikh, 2014). Interestingly, poor sleep has also been linked to increased risk-taking (Baker et al., 2020; Telzer et al., 2013). By following teenagers over time, we can see how anxiety, sleep, and risk-taking behaviors interact and influence each other.

3.2. Neuroimaging Methods

3.2.1. Dynamic Causal Modeling (DCM)

Brain imaging techniques like fMRI allow us to see which parts of the brain are active during certain tasks. But, to understand how anxiety develops, we need to know more than just which areas are "talking" to each other – we need to know who's driving the conversation!

This is where DCM comes in. DCM helps us understand how different brain areas influence each other. Imagine listening to a conversation between three friends: the amygdala, the PFC, and the striatum. DCM helps us figure out who's leading the conversation, who's listening, and how this changes over time (Goldenberg & Galván, 2015).

3.2.2. Reliability

When we talk about brain imaging studies, it's important to know how reliable the results are. In other words, if we scan the same person twice, will we get similar results? This is especially important when studying a developing brain, which is constantly changing (Herting et al., 2018).

Some brain imaging methods are more reliable than others. For example, measuring the size and structure of brain areas is pretty consistent over time (Drobinin et al., 2020). However, fMRI scans can be affected by things like movement, making them a bit less reliable, especially in areas like the amygdala and striatum (Vetter et al., 2017). Interestingly, DCM, despite its complexity, seems to be quite reliable (Frässle et al., 2015; Schuyler et al., 2010).

To improve the reliability of brain imaging studies, researchers can do a few things:

• Make sure participants are comfortable in the scanner to reduce movement.

• Scan participants multiple times with short breaks in between.

• Use different types of brain imaging techniques to get a more complete picture (Herting et al., 2018; Supekar et al., 2010; Liem et al., 2017).

Finally, it's crucial to study a large and diverse group of people. This helps ensure that the findings are generalizable to a wider population (Turner et al., 2018).

4. Conclusion

Anxiety is a common experience, but for some teenagers, it can become a serious problem that affects many areas of their lives. We've learned that anxiety isn't just about avoiding scary things – it's also about how we perceive and respond to rewards. Additionally, the teenage brain is wired to seek out new experiences, and this sometimes involves taking risks.

To truly understand how anxiety develops during adolescence, we need to look at how the different parts of the brain work together, including the amygdala, the striatum, and the PFC. Longitudinal studies, along with advanced brain imaging techniques like DCM, can help us track these changes over time.

By understanding the complex interplay of anxiety, risk-taking, and brain development, we can develop better ways to support teenagers struggling with anxiety and help them navigate the challenges and triumphs of adolescence.

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1. Introduction

Lots of kids start to feel anxious when they become teenagers. More than 31% of teenagers in the US say they feel anxious (Lee et al., 2006; Merikangas et al., 2010). When kids feel anxious, they might avoid things that make them feel scared (Galván and Peris, 2014; Reniers et al., 2016). But at the same time, teenagers are supposed to try new things and take risks. It's a normal part of growing up! It helps them learn and become more independent (Casey et al., 2008). These behaviors can be seen in lots of animals and cultures, too (Brenhouse and Andersen, 2011; Duell et al., 2018; Steinberg, 2008).

So how come teenagers seem to act in opposite ways? How can they be more anxious and more likely to take risks? To understand this, we'll look at what scientists have learned about anxiety and risk-taking in the brain. We'll also see why taking risks as a teenager is actually a good thing - it's how kids learn to be independent and go after what they want (Casey et al., 2008; Spear, 2000). This is much harder to do when someone is anxious and avoids things that make them nervous.

This paper will show that to understand anxiety in teenagers, we have to look at how their brains control both approaching things they want and avoiding things they fear. Most research looks at these two things separately, especially when studying anxiety. To really understand anxiety in teenagers, we need more research that follows kids over time to see how their brains control these behaviors as they grow. This will help us understand why some teenagers get anxious and others don't, spot the kids who might need help, and create better ways to help them.

2. How Anxiety Develops

2.1. What is Anxiety?

Everyone feels anxious sometimes! It's normal to feel nervous or scared when facing something challenging or new. In fact, it can help us stay safe. Feeling anxious can make us avoid danger (Beesdo et al., 2009). This is helpful when we're little (Shechner et al., 2012), but it can become a problem if we keep avoiding things as we get older. If we never learn that something is safe, we might miss out on fun experiences or chances to grow (LeDoux et al., 2017). This is a big concern for teenagers because this is a time when they start to do more things on their own, like trying new activities or hanging out with new friends (Casey et al., 2008).

Most anxiety disorders start in early adolescence - that's around the time one becomes a teenager (Kessler et al., 2007). Over 31% of teenagers in the US experience enough anxiety to be diagnosed with a disorder (Merikangas et al., 2010). Even more feel anxious sometimes, even if they don't have a disorder (Beesdo et al., 2009; Siegel and Dickstein, 2011). If these anxious feelings aren't addressed, they can lead to other problems like depression, addiction, trouble in school, and even suicidal thoughts (Chiu et al., 2016; Kendall et al., 2018; Siegel and Dickstein, 2011; Woodward and Fergusson, 2001). Even though more and more kids are being diagnosed with anxiety (Child Mind Institute, 2018), many kids with anxiety don't get diagnosed or treated (Benjamin et al., 1990; Child Mind Institute, 2018; Green et al., 2019; Merikangas et al., 2010; Siegel and Dickstein, 2011). This is because kids often show their anxiety through behaviors like complaining of stomachaches instead of saying they feel nervous (Siegel and Dickstein, 2011).

Sometimes, before kids even realize they're anxious, they start paying more attention to things that seem scary or dangerous (Shechner et al., 2012). These kids might be more likely to develop anxiety as teenagers, especially if they were very shy or afraid of new things as younger children (Fox et al., 2005; Broeren et al., 2013; Domschke and Maron, 2013; Henderson et al., 2015). These children are almost four times more likely to have an anxiety disorder as teenagers (Chronis-Tuscano et al., 2009; Essex et al., 2010; Schwartz et al., 1999). However, it's important to remember that not all shy kids develop anxiety.

Scientists believe that anxiety changes how the brain pays attention to scary things. There is a part of our brain that notices and reacts to threats called the "salience network," which includes the amygdala and the prefrontal cortex (PFC) (Blackford and Pine, 2012). The amygdala sounds the alarm when it senses danger, and the PFC helps us decide how to react. This network doesn't work quite right in people with anxiety. But it's not just about threats - anxiety also seems to affect how the brain processes rewards. This involves parts of the brain like the striatum (Guyer et al., 2006; Lahat et al., 2018). To truly understand anxiety in kids, we need to study how both the threat and reward systems in the brain change as kids grow up.

2.2. Puberty and the Teenage Brain

Becoming a teenager is a time of big changes, especially in the brain. During puberty, the brain grows new connections, but then it gets rid of some of them in order to make the connections used most often the strongest (Crews et al., 2007). This process can make the brain extra sensitive to both good and bad things. This means that parts of the brain that process emotions, like the ventral striatum (VS) and amygdala, might be more active, making a person crave good feelings and react more strongly to scary or stressful things (Galván, 2013). At the same time, the part of the brain that controls impulses and makes good decisions (the PFC) is still developing (Casey et al., 2008). This difference in development might explain why teenagers take more risks and are more likely to experience negative consequences (Casey and Jones, 2010; Galvan et al., 2006).

Scientists use something called the Triadic Model to explain how teenagers make decisions (Ernst et al., 2009). This model says there are three main systems in our brains: one for approaching good things (reward), one for avoiding bad things (threat), and one for controlling our impulses and making good choices (regulation). These systems work together, and sometimes they compete with each other. For example, when offered a piece of candy, the reward system says, "Yes, candy is delicious!" But then a person might remember that they're not supposed to eat candy before dinner. The regulatory system then kicks in and says, "Wait! Maybe we shouldn't." This model helps us understand why teenagers might take more risks because their reward system might be stronger than their regulatory system.

Let's look at one of these brain areas in more detail. The VS is a part of the brain that processes rewards and is involved in motivation (Derringer et al., 2010; Riccardi et al., 2006; Zuckerman, 1985). It's like the "feel-good" center of the brain, and it gets very active when teenagers experience something rewarding (Galvan, 2010). Recently, scientists have started to think that the VS might also be involved in fear and anxiety (Lago et al., 2017). This is because it's connected to other parts of the brain involved in anxiety, like the amygdala, hippocampus, and ventromedial PFC.

Studies have shown that anxious kids might have differences in how their VS responds to rewards. For example, they might show more activity in their VS when they are waiting for feedback, even if it's negative feedback (Benson et al., 2014). This might be because they are more worried about making mistakes.

Interestingly, studies of shy kids show that they have more activity in their VS when they experience something rewarding (Guyer et al., 2006; Lahat et al., 2018). This might seem counterintuitive, but it could be that they are more sensitive to rewards because they don't experience them as often.

The amygdala and the VS work together to help us make decisions. The amygdala tells the VS how good or bad something is, and then the VS decides whether to approach it or avoid it (Fareri and Tottenham, 2016). For example, if a person sees a piece of chocolate cake, the amygdala will send a message to the VS saying, "This is delicious!" The VS will then decide whether to eat it or not, depending on whether the person is hungry, on a diet, or has other plans. This connection is really important, and it might be disrupted in people with anxiety.

2.3. Risk-Taking and Anxiety

As we learned, taking risks can be scary, but it's also a normal and healthy part of growing up. It helps teenagers learn to be independent and make their own decisions. But what about teenagers who are anxious? Are they less likely to take risks? It turns out it's a bit complicated.

Some studies show that anxious teenagers are less likely to abuse drugs and alcohol (Malmberg et al., 2010). This makes sense, right? If a person scared of taking risks, they probably won't want to try drugs or alcohol. But other studies show the opposite - that anxious teenagers are more likely to abuse drugs and alcohol (Child Mind Institute, 2018; Kilgus and Pumariega, 2009; Low et al., 2008). So which is it?

It's possible that there are different types of anxiety, and some types might actually make kids more likely to take risks (Nicholls et al., 2014). For example, some anxious teenagers might use drugs or alcohol to cope with their anxiety. These teenagers are usually more impulsive and more sensitive to rewards. There might even be a gene that makes some anxious kids more likely to take risks (Ernst et al., 2014)!

It's really important for scientists to understand the different ways that anxiety and risk-taking can interact, especially in teenagers. This is important for understanding why some anxious teenagers engage in risky behaviors and how to help them make healthier choices.

2.4. Threat vs. Thrill

Taking risks doesn't always mean you'll get a reward. Sometimes, it's the thrill of the unknown that's rewarding! Think about riding a rollercoaster, jumping out of an airplane (with a parachute, of course!), or riding a bike without a helmet - it can be scary, but also really exciting! This is because the feeling of danger can actually activate the reward system in our brains (Spielberg et al., 2014). For some people, the thrill of danger can be as addictive as drugs. In fact, there's a therapy program called "Adrenaline Instead of Amphetamine" that helps people who are addicted to drugs like amphetamines by having them do exciting activities like skydiving (Makarowski et al., 2016).

This thrill-seeking behavior is very common in adolescence. Remember how the reward system in a teenager's brain is developing faster than the part that controls impulses? This might make teenagers more likely to find danger rewarding (Dahl, 2004). Think about all the exciting (and sometimes scary) things that teenagers do, like going on dates or trying out for the school play. These experiences can be both nerve-wracking and exhilarating!

It seems like teenagers are more comfortable with uncertainty than children or adults (Van Den Bos and Hertwig, 2017). In fact, they're more likely to take a risk if they don't know what the outcome will be (Tymula et al., 2012). On the other hand, anxiety can make people uncomfortable with uncertainty (Dekkers et al., 2017; Osmanağaoğlu et al., 2018). So, what's scary and uncertain for one person might be thrilling and exciting for another!

Scientists are still trying to figure out exactly how this works in the brain. One study found that teenagers who showed more activity in their amygdala and VS when they were faced with a threat were also more likely to be thrill-seekers (Spielberg et al., 2014). Another study found that teenagers who showed more activity in their VS when they were learning something new under pressure were also better at learning (Depasque and Galván, 2019). This is fascinating because it suggests that the brain areas that process threats and rewards might actually work together to help teenagers learn and grow.

Understanding how the amygdala and VS interact is really important for understanding how anxiety develops in teenagers. If we can figure out how to help teenagers reframe threats as challenges and opportunities for growth, we might be able to prevent anxiety from developing in the first place!

3. Measuring Meaningful Change

3.1. A Need for Longitudinal Studies

Scientists have learned a lot about anxiety in kids by studying their brains. But most of these studies only look at a single point in time. This makes it hard to know how anxiety develops over time. To really understand how anxiety develops, we need to study the same kids over a long period of time. This is called a longitudinal study.

Longitudinal studies are important because they allow scientists to track changes in the brain as kids grow. For example, we know that some kids have trouble sleeping during adolescence, which can make anxiety worse (McMakin and Alfano, 2015). Poor sleep is also linked to more risk-taking behaviors (Baker et al., 2020; Telzer et al., 2013). By following kids over time, scientists can see how sleep problems, anxiety, and risk-taking are related. This information can then be used to develop better ways to prevent and treat anxiety.

3.2. Neuroimaging Methods

3.2.1. Dynamic causal modeling (DCM)

Scientists use special tools to study the brain. One tool is called neuroimaging. Neuroimaging allows scientists to see pictures of the brain and measure brain activity. There are many different types of neuroimaging, and each one provides different information about the brain. One promising type of neuroimaging is called dynamic causal modeling (DCM).

DCM helps scientists understand how different parts of the brain communicate with each other. Remember the amygdala, PFC, and VS we talked about earlier? DCM can show scientists how these areas work together to produce thoughts, feelings, and behaviors. This information is very helpful for understanding how anxiety develops and how to treat it.

3.2.2. Reliability

When scientists are studying the brain, it's important to make sure that their tools are reliable. Reliability means that the tool will give the same results every time it is used.

Not all neuroimaging tools are equally reliable (Herting et al., 2018). Some types of brain scans are very reliable, while others are less so. For example, structural neuroimaging (which shows the size and shape of the brain) is very reliable, while functional neuroimaging (which shows brain activity) can be less reliable. This is because brain activity can be affected by many things, like how much sleep a person got the night before or what a person ate for breakfast.

Scientists are always working to improve the reliability of neuroimaging tools so that they can be more confident in their findings.

4. Conclusion

Anxiety is a common problem for teenagers. It can make it hard to do everyday things like go to school, make friends, and try new things. Left untreated, anxiety can last into adulthood and lead to other problems like depression and substance abuse (Beesdo et al., 2009; Bittner et al., 2007; Broeren et al., 2013; Kessler et al., 2007; Merikangas et al., 2010).

To better understand and treat anxiety, we need to learn more about how the brain develops during adolescence. Specifically, we need to learn more about how the parts of the brain that process rewards and threats interact. We also need to understand why some teenagers who experience anxiety engage in risky behaviors while others do not.

Longitudinal studies that use neuroimaging techniques like DCM are essential for answering these questions. By studying the same teenagers over time, we can track changes in their brains and see how those changes are related to their behavior. This information can then be used to develop more effective treatments for anxiety and help teenagers lead happier, healthier lives.

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