Maturation of neural systems supporting inhibitory control

Adolescence is a unique time in development, demarcated by puberty and characterized by an increase in impulsive sensation-seeking behaviors. In some teenagers, these changes elevate to extreme risk-taking and counter-productive behaviors, in some cases even undermining survival (e.g., careless driving, extreme sports) [1]. This adolescent phenotype has been traditionally attributed to limitations in engaging inhibitory control: the ability to voluntarily suppress a reactive response in order to generate a planned executive goal driven response [2–4]. In recent years, a more nuanced picture has emerged. Inhibitory control is evident early in development [5] with incremental improvements that continue into adulthood [6–8]. By adolescence, cognitive control has improved significantly with evidence for the ability to engage cognitive control systems at adult levels; however, the ability to engage these processes in a flexible and consistent fashion continues to be limited until adulthood [4].

Significant advances in our understanding of the specialization of the neurocognitive systems needed for optimal and reliable adult level inhibitory control have been made in recent years. Human brain imaging studies relying on functional Magnetic Resonance (fMRI) and Magnetoencephalography (MEG) have identified age-related changes in brain areas engaged during inhibitory control, most importantly in the prefrontal (PFC) and anterior cingulate cortex (ACC). Neurophysiological studies in non-human primates have also begun to reveal the neural mechanisms underlying the ability to prepare and effectively inhibit prepotent responses. In this review, we integrate findings about age-related, systems level changes affecting inhibitory control in humans, with ones about the underlying neurophysiology afforded by non-human primate work, to elucidate the neural mechanisms that support the transition from adolescence to adult-level optimal inhibitory control. Understanding the neural basis of the maturation of cognitive control in normative development can also offer insights into impaired development in psychopathologies, which are in general demarcated by disrupted inhibitory control (see Box 1) [9].

We first review the behavioral phenotype of limited inhibitory control during adolescence in humans and non-human primates. Secondly, we review the evidence for brain structural changes in relevant brain systems and their connectivity. Next, we present evidence for age related changes in brain functional processing based on human fMRI and MEG studies, as well as non-human primate neurophysiology. We end by proposing a model of the maturation of inhibitory control that encompasses the lines of evidence accrued through studies in humans and non-human primates.

Behavioral manifestations of inhibitory control

Inhibitory control is measured using tasks that require voluntary cessation of a reflexive response, or suppression of interference from an established response set, to generate a planned goal-driven response determined by an instruction. Examples of paradigms involving stopping a reflexive response include antisaccade (see Glossary), flanker, and stop-signal tasks; and examples of tasks involving suppression of interference include go/no-go and Stroop. From the neural perspective, inhibitory performance requires a number of processes: engaging neural systems that pre-emptively dampen activity of reflexive responses (e.g., premotor regions); increased engagement of executive systems supporting generating a goal driven response (e.g., prefrontal regions); and recruitment of mechanisms that support engaging the abovementioned systems in a ready manner (systems functional integration).

In terms of developmental trajectory, inhibitory control is evident relatively early on, in infancy, as evidenced by the ability of infants to voluntary inhibit responses as required by the abovementioned tasks, albeit inconsistently [5,10]. Performance rapidly improves through childhood [11,12] subsequently showing more subtle yet continued improvement through adolescence [6,13–15]. Importantly, while the ability to generate a single correct inhibitory response is evident early in development, what improves through adolescence is the proportion of trials with correct inhibitory responses [16]. From a neurobiological perspective, this implies that the circuitry that can dampen reflexive sensorimotor responses and select an appropriate action among alternatives is available early in development. Yet the ability to engage systems-level processes that recruit inhibitory and executive circuits in a flexible, controlled, and ready manner, continues to substantially improve through adolescence. As described below, these improvements proceed in parallel with maturation of relevant brain regions.

The antisaccade task [17] (AS) is a particularly useful probe of neurocognitive maturation of inhibitory control both in humans and in non-human primates. In the AS task, subjects are instructed to suppress the prepotent tendency to look toward a salient visual stimulus that appears in an unexpected location, and instead make a voluntary eye movement to its mirror location (Fig. 1A–B). Thus, the AS requires that: (1) a rule be kept on-line (“do not look at an upcoming visual stimulus”); (2) reflexive sensorimotor preparatory processes be dampened; and (3) executive processes for voluntary responses be engaged by a goal (“look in the mirror location”), rather than a sensory stimulus. It is important to note that in addition to inhibitory control, cognitive processes including working memory and attention mechanisms are also engaged, as the task instruction to suppress interference by the distractor needs to be kept on line [18]. As reviewed below, the AS task has been used extensively to understand inhibitory control and its development in humans and non-human primates, providing a wealth of information regarding the behavior, as well as the brain mechanisms behind its late maturation.

Given debates about sex differences in spatial abilities and known sex differences in the timing of puberty, the question arises whether inhibitory control, for instance as assessed via the AS task, displays differences between males and females. To date, the AS task has not revealed any noticeable sex differences. This is perhaps somewhat expected, given that the set of cognitive mechanisms this paradigm engages, in particular core top-down modulation of behavior, are foundational cognitive process across the sexes and do not tend to show marked sex-difference [6]. Of note, however, white matter does mature earlier in females [19,20] thus the developmental trajectory and time of maturation of adult level inhibitory control may differ by sex in more subtle ways that have not yet been identified.

Maturation of inhibitory control performance

Human Adolescence

As mentioned earlier, the ability to generate an inhibitory response is evident in infancy. Specifically, nine-month old infants can select between simultaneously presented locations by inhibiting response to the distractor location, similarly to adults [5,10]. Subsequently, in childhood, there is a steep increase in inhibitory abilities, across a range of inhibitory tasks (see Glossary for definitions of tasks). Flanker tasks, which require suppressing distracting peripheral stimuli, show that interference control significantly improves through childhood with little improvement after adolescence [11]. Similarly, the ability to stop an initiated response in the stop-signal task [13], to change an established response in the go/no-go task [21], and to suppress a learned response in the Stroop task [22], improve significantly into childhood but are mostly adult-like by adolescence. Together, these studies provide compelling evidence regarding the acquisition through childhood of the ability to incrementally apply executive systems to suppress responses.

The antisaccade task is particularly well-suited to probe core inhibitory processes that continue to mature through adolescence. Unlike other inhibitory tasks that require a button press and may be prone to various strategies, the AS requires a saccade response, the fastest movement the body can make. Critical to performing a correct AS is the preparatory period [23,24], which provides a useful quantifiable variable – latency to initiate a correct response – in addition to proportion of correct responses. Several studies have assessed developmental improvements in AS performance, and similar to the abovementioned inhibitory tasks, the most significant improvement occurs through childhood but there is continued significant development through adolescence [14,25–27]. The developmental trajectory is curvilinear [14,25–27], and an inverse function provides best fits to it [6,14,26]. This trajectory depicts steep decreases in error rates (Fig. 1E) and latency of correct responses (Fig. 1F) through childhood, followed by a much lower but still significant slope through adolescence, reaching stability in adulthood (Fig 1B–D). These findings have been confirmed in a longitudinal study assessing participants 8 to 30 years of age [6]. In addition, intra-subject variability in AS latency decreases with age [26,27]. It is typical for subjects, in some of the trials, to display saccadic deviations during the eye movement towards the stimulus, before correcting away the eye movement to the correct location; intra-subject variability in these saccadic deviations, similarly to the AS latency, decrease with age [28]. Interestingly, developmental improvements do not appear to be affected by IQ or sex, indicating that more general components of inhibitory control are being assessed [6]. It is important to note that in childhood 30–50% of trials are correct [14,25,27] underscoring that the ability to perform an AS is available early in development and what improves is the ability to effectively recruit executive processes in a sustained fashion. Also of note, in the presence of impending rewards AS performance in adolescence improves, approximating adult levels reflecting the ability to push the engagement of executive processes for the purpose of reward receipt [29]. Together, these findings establish that the ability to access inhibitory processes in a ready and controlled fashion underlies the transition to mature adult level cognitive control.

Non-human primates

The hallmarks of behavioral maturation in adolescence are observed not only in humans, but also in other primate species. Macaque monkeys age approximately 3 times faster than humans, entering puberty at ~3.5 years of age and reaching full sexual maturity at 5 years [30,31]. A number of physiological markers can be used to ascertain puberty, such as growth in body mass, femur length, testicular size, closure of epiphyseal plates in the bones of the extremities, and serum testosterone concentration [32]. Monkeys can be trained in the AS task (Fig. 1C–D) and tested in adolescence and in adulthood. In a longitudinal experimental study, monkeys were originally trained in the AS task at the time of puberty, allowed to reach asymptotic performance, and behavioral results were obtained through this training period [32]. The animals were then returned to their colony and were not exposed to any behavioral task. A second round of data was then obtained in adulthood, approximately 2 years after the original tests. The monkeys’ performance in the AS task greatly improved between adolescence and adulthood (Fig. 1G). Intra-subject (session-to-session) variability in the proportion of correct trials from session to session is also much greater in the adolescent than in the adult animals. One can wonder whether the improvement in overall performance is the result of slower reaction times in adult animals, which could afford them more time to process and resist the prepotent effect of the visual stimulus. In fact, the picture was quite the opposite, and consistent with results from humans: reaction times in monkeys were faster in adulthood than in adolescence (Fig. 1H). Furthermore, improvements in performance in adulthood were generally greater in more demanding versions of the AS task, e.g. the “gap” version, which involves turning off the fixation point before the appearance of the visual stimulus and thus making it more difficult to resist an eye movement at the stimulus onset [32].

Neural systems maturation

Human Structural and Functional Developmental Changes

The adolescent brain is undergoing maturation in parallel to improvements in inhibitory control. Magnetic Resonance Imaging (MRI) studies in humans show that gray matter volume decreases into adulthood, with areas of the association cortex including the prefrontal cortex continuing to mature in adolescence [33]. The striatum and thalamus, both of which are connected to fronto-parietal cortical regions, also continue to mature through adolescence [34]. Decreases in gray matter thickness are thought to be associated with synaptic pruning, which postmortem studies show proceeds from childhood into the third decade of life in prefrontal cortex [35].

White matter connectivity also shows significant changes through childhood and adolescence. Diffusion Tensor Imaging (DTI) studies show that the integrity of white matter tracts predominantly increases through childhood reaching adult levels by mid-adolescence, including the superior longitudinal fasciculus which provides connectivity between dorsal prefrontal and parietal regions [20,36]. However, within the basal ganglia integrative zones that determine action the relative extent of affective projections in relation to projections from cognitive control systems decreases with age. This age-related change was attributable solely to age-related decreases in affective inputs as cognitive inputs were stable by adolescence. Importantly, these changes were found to mediate the abovementioned greater sensitivity in adolescence to rewards when performing the AS [37]. White matter specialization through development is believed to be subserved, in part, by myelination of tracts proceeding in a Hebbian ‘use it or lose it’ fashion, predominantly fortifying the tracts that are used more frequently.

Resting state fMRI has also shown developmental progressions through adolescence. In particular, there is evidence for decreases in functional connectivity between prefrontal and subcortical regions, including frontostriatal [38,39] and frontoamygdalar [40] connectivity. These changes are thought to reflect, in part, the decreasing influence of affective processes through adolescence. At the network level, the overall network organization is established by childhood, but internetwork connectivity that engages prefrontal systems (cingulo- opercular/salience networks) with other networks, including sensory ones, strengthens through childhood into adolescence [41,42]. Taken together, evidence indicates that prefrontal connectivity with brain regions that require top-down processes for optimal and sustained inhibitory control, continues to mature through adolescence.

Maturation of Non-Human Primate Frontal Connectivity

Anatomical studies in monkeys demonstrate that inhibitory synapses of interneurons onto pyramidal neurons in the prefrontal cortex strengthen in adolescence [43]. The connections of parvalbumin interneurons, in particular, have been found to continue to mature into adulthood [44]. It may be tempting to link stronger inhibitory synaptic connections with improved inhibitory control at the behavioral level, but the effects of synaptic maturation are likely to be more indirect, in concert with the idea that cognitive mechanisms of inhibition may not be equated with neural ones [18]. Analysis of simultaneously recorded spike trains with extracellular electrodes also confirms that the overall strength of intrinsic effective prefrontal connectivity increases between the time of adolescence and adulthood [45]. Synaptic projections of neurons releasing neuromodulators, most importantly dopamine, continue to mature in adolescence [46], and computational models suggest that optimal dopamine levels may be linked to improved signal-to-noise stimulus representations [47]. Collectively, these findings suggest that adolescence is characterized by a reorganization of prefrontal circuits at the macro- (between areas) and microscopic (between neurons) levels. The functional consequences of this circuit maturation are readily observable in imaging and neurophysiological experiments.

Neurofunctional changes in adolescence

Human fMRI

fMRI studies of the development of inhibitory control show both age-related increases and decreases in prefrontal engagement [48–50]. These results, however, are not necessarily contradictory. Working on a model where adult brain function is considered the optimal mature processing, increased prefrontal activity in youth reflects greater effort to generate an inhibitory response similar to increased function with more cognitive load in adults [51]. Decreased activity would reflect inability to engage systems at optimal levels [52], as decreased blood-oxygen-level-dependent (BOLD) responses are known to result from greater synchronization of relevant prefrontal systems [53]. Accumulating evidence indicates that when considering correct trials, children show greater engagement of prefrontal systems [6,54] that is associated with better performance [6,55].

Most studies have been cross-sectional, which can be challenged by cohort effects. The one longitudinal fMRI that investigated inhibitory control found that prefrontal engagement when generating correct antisaccades was greatest during childhood, but by adolescence dorsolateral prefrontal cortex (dlPFC) was engaged at adult levels (Fig. 2A–B) [6]. The dorsal anterior cingulate cortex (dACC), which was correlated with performance, showed increasing engagement through adolescence mediating behavioral developmental improvements in AS performance (Fig. 2C–E). Age related increases in anterior cingulate function during inhibitory control have been found with fMRI in studies using Stroop, AS, and stop signal tasks [22] as well as with EEG [56,57]. The dACC is known to support performance monitoring [58] and works as an alerting system to engage cognitive control systems [59]. Thus, during adolescence immaturities in error processing may play a critical role in limitations in inhibitory control.

As discussed above, potential rewards have an impact on AS performance enhancing the ability to suppress saccades particularly in adolescence. Studies have found that during rewarded AS trials in adolescence, there is greater activation in the nucleus accumbens (NAcc) [60,61], a region rich in dopaminergic inputs and known to underlie reward processing [62,63]. Adolescents also showed greater activity in the Frontal Eye Fields (FEF), a primary region supporting AS performance, compared to adults during correct rewarded AS responses suggesting that adolescents may be exerting greater effort to perform a task that is difficult in order to obtain a reward. Thus, increased engagement of the NAcc may impact the degree that systems underlying the ability to obtain reward receipt are engaged in adolescence. When probing associations with the Zuckerman Sensation Seeking Scale, which characterizes sensation seeking traits and predispositions for thrill and risk-taking behaviors, there is no clear association with AS performance [64]. However, activation of the NAcc during the rewarded AS was found to have unique associations with sensation seeking through development. Greater NAcc activity in childhood and early adolescence was linked to reduced sensation seeking, whereas subsequently in later adolescence, greater NAcc activation was associated with greater sensation seeking [64]. These results suggest that as the system is maturing in later adolescence, inhibitory control in the presence of rewards reflects increased sensation seeking.fMRI studies have also found that the ability of the PFC to engage other brain systems in a top-down fashion plays an important role in developmental improvements in AS performance. Granger causality analyses found a significant age related increase in the number of significant connections and the strength of effective functional connectivity from PFC to other cortical and subcortical regions supporting the integration of frontal, oculomotor, and subcortical systems [65]. These results suggest that core local processing of prefrontal systems undergo significant maturation in childhood and are available at adult levels by adolescence; however, prefrontal engagement with other cortical and subcortical regions continues to strengthen into adolescence, which may underlie the lack of reliable and ready adolescent engagement of executive systems.

Human MEG

Magnetoencephalography (MEG) affords a temporal resolution at the millisecond level, allowing characterization of electrophysiological activities generated by neuronal dynamics throughout different phases of cognitive processing. MEG has indicated that Global Field Power has a delayed progression in adolescents compared to adults when performing a go/no-go task, suggesting immaturities in the ability to generate voluntary inhibitory responses [66]. Similarly, EEG studies show the importance of oscillatory activity in the preparatory period of the AS where increases in medial frontal theta and suppression of posterior alpha precede correct responses [24]. A developmental MEG study, focused on the preparatory period while performing antisaccades and prosaccades, showed marked differences in oscillatory activity in adolescents compared to adults that corresponded with performance [23], [67]. Adolescents showed adult level beta-band power in dlPFC but lower Frontal Eye Field (FEF) alpha-band power (Fig. 3A) and beta/alpha dlPFC/FEF cross-frequency coupling (Fig. 3G). Beta rhythms have been associated with cortical glutamatergic function in deep layers [68], through top down inputs activating pyramidal neurons. Alpha rhythms have been associated with dampening of neuronal activities through inhibitory processes [69] supporting inhibitory mechanisms in the AS task [70]. These results, consistent with ideas discussed earlier, indicate that dlPFC executive systems are on-line by adolescence, but prefrontal systems are not readily engaged during executive responses, undermining optimal inhibitory control.

Developmental Neurophysiology in Non-human Primates

Compared to analyses using non-invasive approaches, neurophysiological studies in monkeys have provided a more granular picture of developmental changes that occur at the level of single neurons in the context of inhibitory control maturation. As mentioned, the AS task proved particularly productive in this context. In principle, the developmental improvements in AS performance could be associated with lower neuronal activity elicited by the stimulus (i.e. more effective filtering of the prepotent stimulus that needs to be resisted) or by more effective representation of the correct target of the eye movement (i.e. enhancement of the goal). Neurophysiological studies reveal that the latter is the case (Fig. 2F–K). The activity of neurons representing the location of where the eventual eye movement needs to be directed is greater in the PFC of adult animals [32]. What is most enhanced is the activity representing the vector inversion (see Glossary), the shift of attention and preparation of a response away from the stimulus. The change was primarily localized in the prefrontal cortex, compared to the posterior parietal cortex [71]. In contrast, neurons with purely eye-movement driven responses exhibited similar activity at the two developmental stages reflecting similar processing of the presence of a target. Of note, the total level of activity, integrated across the entire period of the task and across all populations of neurons, exhibited only subtle differences between adolescence and adulthood; it was the precise timing of activation for different stimulus conditions that revealed the functional maturation. These results provide evidence that there are important developmental improvements in engaging neural systems that support generating an executive planned response in the AS task that may contribute to the ability to suppress the reflexive response.

Neurophysiological studies have also confirmed that the preparatory period of the AS task is critical for a successful inhibitory response [23]. As in humans, alpha oscillations modulate preparatory activity in non-human primates; alpha power in deep cortical layers provides a pulsed inhibition signal to deeper and upper cortical layers. [72]. Accordingly, changes in neuronal activity between non-human primate adolescence and adulthood have been found in neurophysiological recordings from the preparatory fixation period [71]. Baseline activity was higher overall in the adult group and increased (“ramped”) with a faster rate prior to the onset of the stimulus (Fig. 3C). The level of this activity was also predictive of behavior, as correct trials were characterized by a higher firing rate prior to the onset of the stimulus. Neuronal firing in the fixation period is likely driven by the activity encoding task and rule contingencies necessary to perform the AS task that engage preparatory inhibitory processes. As mentioned above, activity preceding the onset of the stimulus in saccadic tasks is predictive of errors in human EEG and fMRI experiments [73–75]. Additionally, examining responses on a neuron-by-neuron basis (Fig. 3B–F) determined that neurons that exhibited the highest levels of baseline activity in the AS task also exhibited higher levels of delay period activation in the working memory tasks, performance which also improved between adolescence and adulthood [76]. These results demonstrate that preparatory processes are critical for response inhibition and represent a neural resource shared between multiple cognitive functions, which mature in tandem between adolescence and adulthood.

Concluding Remarks

Taken together, human neuroimaging studies and animal neurophysiology delineate the specific processes that underlie the maturation of inhibitory control. Based on these studies, a primary way in which inhibitory control matures is the emergence of neural activity patterns that establish a ready preparatory state to inhibit a response. The ability to engage these preparatory systems may be mediated by improved computations afforded by increases in inhibitory circuitry and the ability to integrate systems level processes. These developmental changes support PFC integration, including error processing and planning an effective response. Importantly, adolescent immaturities in these brain processes do not undermine the ability to generate inhibitory responses but limit the ability to engage cognitive control in a sustained and controlled fashion.

The AS task involves, in addition to processes that are specific to inhibitory control, other cognitive processes that are also actively maturing in adolescence, such as working memory and attention, and these may contribute to improvement in task performance over adolescence. Working memory systems are known to undergo a protracted maturation through adolescence in humans and monkeys [76,77]. Working memory is engaged in AS, as the task instruction to inhibit a saccade is maintained online to guide behavior. Working memory development through adolescence, similarly to the maturation of other cognitive functions as discussed earlier, has also been found to rely on systems other than PFC such as visual association cortex. Attention and eye movement circuitries are greatly overlapping [78] as these systems are largely dependent on each other. It is the effective top-down modulation of these neural systems that is core to AS performance and the primary substrate of inhibitory control development during adolescence.

This neural profile of limitations in readily engaging inhibitory control in adolescence may be associated with the recognized phenotype of impulsivity in adolescence and sensation seeking. Impulsivity is characterized by reactive actions directed towards immediate rewards, and that are lacking in forethought [79]. Relatedly, sensation seeking is characterized by the drive to obtain novel experiences that result in increased reward sensations and motivate exploration often involving impulsivity [80]. As such, sensation seeking in adolescence is an adaptive process present across species and societies, believed to motivate exploration and information seeking needed to specialize systems defining adult modes of operation [1]. Sensation seeking however can sometimes lead to risk-taking undermining survival. The AS task is not a direct measure of these behavioral traits and, as discussed above, a link between sensation seeking and AS performance is not readily found except in the engagement of the NAcc in later adolescence. Nevertheless, we would argue, the AS task probes core neural processing that underlie the top-down executive systems inherent in these constructs. That is, the ability to suppress the prepotent reactive saccade to a visual stimulus in the AS requires that neural circuitry that engages executive prefrontal systems to inhibit reflexive subcortical systems be effectively recruited in a timely fashion. Impulsivity and sensation seeking are similarly subserved by a failure in engaging executive prefrontal systems to stop a subcortical reactive reward driven response. Thus, immaturities evident in the systems underlying AS performance reflect a state of development of predisposition for reactive behaviors. Further evidence however is needed to establish a more definitive link between core AS inhibitory control and the more complex motivational processes involved in sensation seeking. Delayed discounting tasks that require choosing a waiting period before receiving a large reward rather than an immediate smaller reward are valuable in characterizing the ability to contextualize suppression of a reactive response. Delayed discounting improves into adolescence [81] (i.e., subjects are able to wait longer for large rewards) adding to the profile of sensation seeking. Associations between AS performance and delayed discounting could further the ability to link maturity of executive top down circuitry and sensation seeking.

Together, human and non-human primate studies show that in adolescence – a time of increased reactive behavior including sensation seeking – inhibitory control is limited, and its neurobiological underpinnings are immature, particularly in the ability to engage top-down executive systems in an effective manner (see Outstanding Questions). Importantly, a failure to normatively strengthen inhibitory systems may play an important role in psychopathology, which across illnesses is associated with impaired response inhibition.

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Neural Maturation Supporting Inhibitory Control

Introduction

Inhibitory control, the ability to suppress reactive responses and generate planned executive actions, improves gradually from infancy through adolescence. This maturation is paralleled by significant changes in the brain's structure and function. Here, we integrate findings from human neuroimaging and non-human primate neurophysiology to elucidate the neural mechanisms underlying the transition to adult-level inhibitory control.

Behavioral Manifestations of Inhibitory Control

Inhibitory control is evident early in development, but the proportion of correct inhibitory responses improves significantly through adolescence. The antisaccade task, which requires suppressing a reflexive eye movement towards a visual stimulus and instead making a voluntary movement to its mirror location, is a particularly useful probe of inhibitory control. Performance on this task improves steeply through childhood, with continued significant improvement through adolescence.

Neural Systems Maturation

Structural and Functional Changes

MRI studies show that gray matter volume in the prefrontal cortex and other brain regions involved in inhibitory control continues to decrease into adulthood. White matter connectivity also strengthens through adolescence, particularly in tracts connecting the prefrontal cortex to other brain areas. Resting state fMRI reveals decreased functional connectivity between prefrontal and subcortical regions, suggesting a reduced influence of affective processes.

Non-Human Primate Studies

In non-human primates, inhibitory synapses in the prefrontal cortex strengthen during adolescence. Electrophysiological recordings show that the overall strength of prefrontal connectivity increases between adolescence and adulthood.

Neurofunctional Changes in Adolescence

Human fMRI

fMRI studies indicate that adolescents show greater prefrontal engagement when generating correct inhibitory responses compared to adults. However, the dorsal anterior cingulate cortex, which is involved in performance monitoring, shows increasing engagement through adolescence, mediating behavioral improvements.

Human MEG

MEG studies reveal that adolescents have delayed global field power progression compared to adults during inhibitory tasks. EEG studies show that preparatory theta and alpha oscillations in the prefrontal cortex are important for successful inhibition.

Non-Human Primate Neurophysiology

Neurophysiological recordings in non-human primates demonstrate that the activity of neurons representing the correct eye movement target is enhanced in adult animals. Preparatory activity in the prefrontal cortex is also higher and increases faster in adults prior to stimulus onset, predicting successful inhibition.

Conclusion

Evidence from human and non-human primate studies suggests that the maturation of inhibitory control involves the emergence of neural activity patterns that establish a preparatory state for response inhibition. This preparatory activity is supported by improved inhibitory circuitry and the ability to integrate systems-level processes, including error processing and response planning. Adolescent immaturities in these processes limit the ability to engage cognitive control in a sustained and controlled manner, contributing to the increased impulsivity and sensation-seeking observed during this developmental stage.

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Development of Brain Systems Supporting Impulse Control

Introduction

As teenagers mature into adults, they typically become better at controlling their impulses and making thoughtful decisions. This improvement in impulse control is linked to changes in the brain that occur during adolescence. By understanding how the brain develops during this time, we can gain insights into why teenagers may be more prone to impulsive behavior and how these changes contribute to adult-level impulse control.

Behavioral Changes in Adolescence

During adolescence, individuals show a gradual improvement in their ability to suppress automatic responses and make planned, goal-directed actions. For example, in the antisaccade task, where participants must look away from a flashing light, teenagers make more errors and take longer to respond correctly than adults. This suggests that adolescents have difficulty inhibiting the automatic response to look at the light.

Brain Structural and Functional Changes

As the brain matures during adolescence, several structural and functional changes occur that support impulse control. The prefrontal cortex, a region involved in planning and decision-making, continues to develop and strengthen its connections with other brain areas. Additionally, the connections between the prefrontal cortex and subcortical regions, such as the striatum and amygdala, which are involved in reward and emotion processing, become more refined.

Neurofunctional Changes from fMRI and MEG Studies

Brain imaging studies using fMRI and MEG have shown that adolescents engage the prefrontal cortex differently than adults when performing tasks that require impulse control. While adolescents may show similar levels of activity in the prefrontal cortex as adults, they have difficulty consistently engaging these systems. This suggests that the ability to recruit and utilize prefrontal systems for impulse control is still developing in adolescence.

Neurophysiological Changes in Non-Human Primates

Studies in non-human primates have provided further insights into the neural mechanisms underlying the development of impulse control. These studies have shown that the activity of neurons in the prefrontal cortex that represent the planned eye movement in the antisaccade task is stronger in adult animals compared to adolescents. Additionally, preparatory activity in the prefrontal cortex prior to the onset of the stimulus is higher in adults and predicts successful impulse control.

Conclusion

The development of impulse control in adolescence is a complex process involving changes in brain structure, function, and neurophysiology. These changes support the ability to engage prefrontal systems that inhibit automatic responses and promote planned, goal-directed behavior. While adolescents may have the capacity for impulse control, their ability to consistently and effectively engage these systems is still maturing. This developmental trajectory may contribute to the increased impulsivity and sensation-seeking behaviors observed in adolescence.

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How The Brain Learns to Control Impulses

Teenagers often find themselves acting on impulse, without thinking about the consequences. This is because their brains are still developing the ability to control their impulses, known as inhibitory control.

What is Inhibitory Control?

Inhibitory control is like a person putting the brakes on their actions. It helps people stop themselves from doing things they shouldn't, like blurting out something rude or eating too much junk food.

How The Brain Develops Inhibitory Control

As people grow older, their brains go through some major changes. The prefrontal cortex, the part of the brain responsible for planning and decision-making, gets stronger. It also becomes better connected to other parts of the brain that help control impulses.

The Antisaccade Task: A Test of Inhibitory Control

Scientists use a task called the antisaccade task to measure inhibitory control. In this task, the subject has to look away from a flashing light instead of towards it. This is hard because the brain is naturally drawn to bright lights.

How Teenagers Perform on the Antisaccade Task

Studies have shown that teenagers make more mistakes on the antisaccade task than adults. They also take longer to correct their mistakes. This suggests that their inhibitory control is still developing.

Why is Inhibitory Control Important?

Good inhibitory control is important for many things, like:

• Making good decisions

• Resisting peer pressure

• Controlling our emotions

• Staying out of trouble

How Brain Matures to Improve Inhibitory Control

As people get older, their brains develop in ways that help them improve our inhibitory control. For example:

• The connections between neurons in the prefrontal cortex get stronger.

• The brain releases chemicals that help us focus and control our impulses.

• We learn from our experiences and develop strategies for controlling our impulses.

Conclusion

Inhibitory control is an important skill that takes time to develop. Teenage brains are still maturing, so it's normal for them to have some difficulty with impulse control. However, as they get older, their brains will continue to develop and they will become better at inhibiting their actions. This will help them make better decisions and live more successful lives.

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How The Brain Learns to Self Control

As people grow up, they get better at controlling our actions and making good decisions. This is because the brain is still developing and learning how to help people stop and think before they act.

What is Inhibitory Control?

Inhibitory control is like a superpower that helps people stop themselves from doing things they shouldn't. It's like when someone wants to eat a cookie, but they know they should wait until after dinner. The brain uses inhibitory control to help them resist the cookie and make the better choice.

How The Brain Changes as People Grow

When kids are younger, their brains are still figuring out how to use inhibitory control. It's like they have the tools, but they don't always know how to use them properly. As they get older, their brains get better at connecting different parts together and using the right tools for the job.

What Scientists Have Learned

Scientists have used special machines to take pictures of brains while people are trying to control their actions. They've also studied monkeys, who have brains that are similar to humans.

These studies have shown that as people get older, their brains get better at preparing to stop an action. It's like their brains are getting ready to hit the brakes before they even need to. This helps them make better decisions and avoid doing things they might regret.

Why It's Important

Having good inhibitory control is important for lots of things in life. It helps people stay safe, make good choices, and get along with others. When a person's inhibitory control isn't working well, they might have trouble controlling their impulses or making good decisions.

Conclusion

The brain is an amazing organ that is constantly learning and growing. As people get older, their brains get better at helping them control their actions and make good choices. This ability is important for living a healthy and successful life.

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