Adolescence is a developmental period characterized by suboptimal decisions and actions that are associated with an increased incidence of unintentional injuries, violence, substance abuse, unintended pregnancy, and sexually transmitted diseases. Traditional neurobiological and cognitive explanations for adolescent behavior have failed to account for the nonlinear changes in behavior observed during adolescence, relative to both childhood and adulthood. This review provides a biologically plausible model of the neural mechanisms underlying these nonlinear changes in behavior. We provide evidence from recent human brain imaging and animal studies that there is a heightened responsiveness to incentives and socioemotional contexts during this time, when impulse control is still relatively immature. These findings suggest differential development of bottom-up limbic systems, implicated in incentive and emotional processing, to top-down control systems during adolescence as compared to childhood and adulthood. This developmental pattern may be exacerbated in those adolescents prone to emotional reactivity, increasing the likelihood of poor outcomes.

Adolescence has been characterized by risk-taking behaviors that can lead to fatal outcomes. This study examined the neurobiological development of neural systems implicated in reward-seeking behaviors. Thirty-seven participants (7-29 years of age) were scanned using event-related functional magnetic resonance imaging and a paradigm that parametrically manipulated reward values. The results show exaggerated accumbens activity, relative to prefrontal activity in adolescents, compared with children and adults, which appeared to be driven by different time courses of development for these regions. Accumbens activity in adolescents looked like that of adults in both extent of activity and sensitivity to reward values, although the magnitude of activity was exaggerated. In contrast, the extent of orbital frontal cortex activity in adolescents looked more like that of children than adults, with less focal patterns of activity. These findings suggest that maturing subcortical systems become disproportionately activated relative to later maturing top-down control systems, biasing the adolescent's action toward immediate over long-term gains.

Background-Adolescence is a transition period from childhood to adulthood that is often characterized by emotional instability. This period is also a time of increased incidence of anxiety and depression underscoring the importance of understanding biological substrates of behavioral and emotion regulation during adolescence. Developmental changes in the brain in concert with individual predispositions for anxiety may underlie the increased risk for poor outcomes reported during adolescence. We tested the hypothesis that difficulties in regulating behavior in emotional contexts in adolescents may be due to competition between heightened activity in subcortical emotional processing systems and immature top-down prefrontal systems. Individual differences in emotional reactivity may put some teens at greater risk during this sensitive transition in development.

This study examines important developmental differences in patterns of activation in the prefrontal cortex during performance of a Go-No-Go paradigm using functional magnetic resonance imaging (fMRI). Eighteen subjects (9 children and 9 adults) were scanned using gradient echo, echo planar imaging during performance of a response inhibition task. The results suggest four general findings. First, the location of activation in the prefrontal cortex was not different between children and adults, which is similar to our earlier pediatric fMRI results of prefrontal activation during a working memory task (Casey et al., 1995). Second, the volume of activation was significantly greater for children relative to adults. These differences in volume of activation were observed predominantly in the dorsal and lateral prefrontal cortices. Third, although inhibitory processes have typically been associated with more ventral or orbital frontal regions, the current study revealed activation that was distributed across both dorsolateral and orbitofrontal cortices. Finally, consistent with animal and human lesion studies, activity in orbital frontal and anterior cingulate cortices correlated with behavioral performance (i.e., number of false alarms). These results further demonstrate the utility of this methodology in studying pediatric populations.

Adolescence is a developmental period that entails substantial changes in affective and incentive-seeking behavior relative to both childhood and adulthood, including a heightened propensity to engage in risky behaviors and experience persistent negative and labile mood states. This review discusses the emotional and incentive-driven behavioral changes in adolescents and their associated neural mechanisms, focusing on the dynamic interactions between the amygdala, ventral striatum, and prefrontal cortex. Common behavioral changes during adolescence may be associated with a heightened responsiveness to incentives and emotional cues while the capacity to effectively engage in cognitive and emotion regulation is still relatively immature. We highlight empirical work in humans and animals that addresses the interactions between these neural systems in adolescents relative to children and adults, and propose a neurobiological model that may account for the nonlinear changes in adolescent behavior. Finally, we discuss other influences that may contribute to exaggerated reward and emotion processing associated with adolescence, including hormonal fluctuations and the role of the social environment.

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Objective: To examine the relation between specific frontostriatal structures (prefrontal cortex and basal ganglia) and response inhibition deficits observed in attention-deficitlhyperactivity disorder (ADHD). Method: Children with ADHD and age-matched normal controls were scanned using magnetic resonance imaging (MRI) and tested on three response inhibition tasks. Behavioral performance was correlated with MRI-based anatomical measures of frontostriatal circuitry (prefrontal cortex and basal ganglia) implicated in ADHD. Results: First, significant differences in performance by children with ADHD and normal volunteers were observed on all three response inhibition tasks. Second, performance on these tasks correlated only with those anatomical measures of frontostriatal circuitry observed to be abnormal in children with ADHD (e.g., the region of the prefrontal cortex, caudate, and globus pallidus, but not the putamen) in the authors' previous study. Third, significant correlations between task performance and anatomical measures of the prefrontal cortex and caudate nuclei were predominantly in the right hemisphere, supporting a role of right frontostriatal circuitry in response inhibition and ADHD. Conclusion: The data suggest a role of the right prefrontal cortex in suppressing responses to salient, but otherwise irrelevant events while the basal ganglia appear to be involved in executing these behavioral responses.

Brain magnetic resonance images (MRI) of 104 healthy children and adolescents, age 4-18, showed significant effects of age and gender on brain morphometry. Males had larger cerebral (9%) and cerebellar (8%) volumes (P < 0.0001 and P = 0.008, respectively), which remained significant even after correction for height and weight. After adjusting for cerebral size, the putamen and globus pallidus remained larger in males, while relative caudate size was larger in females. Neither cerebral nor cerebellar volume changed significantly across this age range. Lateral ventricular volume increased significantly in males (trend for females), with males showing an increase in slope after age 11. In males only, caudate and putamen decrease with age (P = 0.007 and 0.05, respectively). The left lateral ventricles and putamen were significantly greater than the right (P = 0.01 and 0.001, respectively). In contrast, the cerebral hemispheres and caudate showed a highly consistent right-greater-than-left asymmetry (P < 0.0001 for both). All volumes demonstrated a high degree of variability. These findings highlight gender-specific maturational changes of the developing brain and the need for large gender-matched samples in pediatric neuropsychiatric studies.