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468 Conclusionscentral role in emotional responses. Evidence suggests that the developmentalcourse is not as protracted as the PFC. It is not surprising that dysfunction in theseregions is posited to subserve symptoms of mood disorder and sociointerpersonaldeficits that arise in adolescence.The striatum (caudate, putamen, and nucleus accumbens) may be among theearlier maturing brain regions. It is most often cited in relation to the etiology ofserious, often chronic, disorders that are assumed to involve congenital origins,including genetic factors and prenatal insults. Schizophrenia and mood disorderswith psychotic features fall in this category, and often entail signs of risk in earlychildhood. This region may also play a role in the onset of sensation-seeking needsthat are hypothesized to underlie the onset of risky behavior in adolescence suchas drug use, sex, gambling, and self-injurious behavior.Preventive Intervention: Time Is of the Essence!The developmental models and theories of neural mechanisms discussed abovehave provided a foundation for the authors in this volume to speculate on promisingpreventive interventions. It is clear that past assumptions about the unidirectionalrelation between biology and behavior are not valid. The individual’sbiological constitution is not fixed by genetics and does not have immutable effectson behavior. Instead, we see that the relation between biology and behavioris complex and bidirectional. Environmental factors, including the psychosocialenvironment, influence brain structure, function, and development. In part, this ismediated by the effects of the environment on the expression of genes. Further,both the environment and the brain affect behavior.These new insights in developmental neuroscience have changed our views ofthe opportunities for preventive intervention. First, we now realize that we canenhance brain functioning by reducing stress and improving the quality of thepsychosocial environment, not only by the administration of drugs. Second, wehave a greater appreciation for the importance of timing these interventions tooptimize neuromaturation.Early Childhood Stress and TraumaEffects of stress during pregnancy and early development suggest that this periodcan have lasting effects on later development of mental disorder. High levels ofstress can sensitize the HPA system (see Gunnar, chapter 6) and influence geneticexpression of various stress responses, including impaired cognitive functioningunder stressful conditions (see Meaney, chapter 7). Meaney’s research suggeststhat these effects are mediated by the nurturing behavior of the primary caregiver,which in his animal models is the female rat. Neglectful and nonnuturing parentingin this model produces genetic effects that influence the parenting behavior of