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Conclusions 467associated with mental disorders may arise more gradually following the onset ofpuberty, and hormones may be implicated (Karen Bales & Sue Carter, chapter 8).A mechanism for this is suggested by the increasing evidence that gene expressionchanges with development and experience, and that hormones play a role inthe expression of genes (Scott Hemby & Joann O’Connor, chapter 5). It has beensuggested that the rise in risk for various mental disorders during adolescence maybe a consequence of the effects of gonadal and adrenal hormones on the expressionof genes that confer vulnerability for these disorders (Walker, McMillan, &Mittal, chapter 12). Thus, hormonal surges during puberty may trigger the expressionof a gene, or more likely, multiple genes, that code for an abnormality in brainfunction.In summary, the models that have attempted to account for the emergence ofpsychiatric symptoms and syndromes during adolescence vary with respect towhether they assume that postpubertal neuromaturational process are intact versusdisrupted, and whether they assume the existence of a congenital versus graduallydeveloping brain abnormality. It is likely that all of the above models have validityfor at least some disorders. It may be that substance abuse and mood disorders, forexample, are less likely to involve congenital vulnerability and more likely to entailan interaction between environmental factors and normal brain maturation. Forschizophrenia and major mood disorders, however, both congenital vulnerabilityand abnormal adolescent brain development may be key etiologic factors.The Neural Mechanisms in VulnerabilityMoving to the level of specific neural mechanisms, the chapters in this volumehighlight both specific and nonspecific associations between various brain regionsand disorders. It is clear that the prefrontal cortex (PFC), especially the dorsolateralprefrontal cortex, is prominent in many of the discussions. It shows a protractedcourse of development and may be the last region to come fully online.The “executive functions” subserved by the PFC appear to play an important rolein a range of disorders. It is a focal point of developmental models of disorders ofbehavioral inhibition that often first emerges in the postpubertal period. For somebehavioral problems that involve deficits in impulse control, such as attention,substance abuse, and conduct disorders, the PFC may indeed be the key region.For other disorders, such as the psychoses, the PFC may play a secondary role, inthat it determines how vulnerabilities in other regions are behaviorally expressed.Given the ability of the PFC to modulate the response of other brain regions, it isoften the target of interventions designed to enable coping with stressors and otherchallenges to mental health.The limbic system, typically assumed to include the amygdala, hippocampus,and limbic regions of the cortex (cingulate gyrus and entorhinal cortex), plays a