Cerebral maturation in adolescence: behavioral vulnerability

Recent neurodevelopmental research has been focusing on the transition period of adolescence into adulthood. This growing interest was spurred by the long-standing realization of the high cost of this transition period in terms of morbidity and mortality, and the emergence of research tools that permit direct examination of brain function in humans. The cost of reaching adulthood is understood as resulting from the typical behavioral and environmental changes that accompany adolescence [4]. The present review describes how the current research helps formulate neurobiological models that can be used to guide future work. One example of such a model, the triadic neural systems model [8], will be examined in more detail. This review will proceed in three stages. First, we will show how neural development results from the confluence of maturational changes that are quantitatively and qualitatively heterogeneous across brain regions, neurochemical and molecular systems. This normative developmental heterogeneity is translated into typical adolescent behavioral patterns, including risk-taking, novelty-seeking, emotional intensity and lability, and peer-group social primacy [5, 9]. Second, based on the notion that motivated behavior can be operationally decomposed into the three core modules of approach, avoidance and control, any alteration in the balance of these three core entities can affect behavior in unique ways. This formulation will serve as the foundation of the neural systems model framework proposed in this review. Third, functional neuroimaging is being used to examine how neural systems underlie this balance within the neural systems model. We will provide a summary of the state of research in this area. Finally, we will show how this research is important for understanding not only normal development, but also the psychopathology. The role of genetic or environmental factors will not be addressed here, despite their critical roles in determining and modulating the balance among the nodes of the triadic model.