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Chapter 1The Developing Brain and Adolescent-Typical Behavior PatternsAn Evolutionary ApproachLinda SpearBrain development is a lifelong process. The massive growth and differentiation ofthe nervous system occurring prior to birth and during the early postnatal period isjust one phase in its gradual elaboration and sculpting. During toddler- and childhood,developmental changes in brain continue to be elaborated (see Ornitz, 1996,for review), even in forebrain regions including the prefrontal cortex (see Happaneyet al., 2004), whose ontogeny is relatively protracted, with significant remodelingduring adolescence and into adulthood (e.g., Sowell et al., 2003). It is now knownthat myelination and associated developmental shifts in gray/white matter volumecontinue in neocortical regions well into adulthood (Sowell et al., 2003) and thatmodest numbers of new neurons are generated in certain locations in brain throughoutlife (Eriksson et al., 1998), potentially providing continued opportunities for someremodeling and plasticity. Within this framework of a developmentally dynamicbrain throughout life, it has gradually become recognized that the adolescent periodis a time of particularly dramatic developmental change. These adolescentassociatedbrain changes include a considerable loss of synaptic connections in certainbrain regions, and ultimately transform the more energy utilizing, seeminglyless efficient brain of the child into a more rapidly communicative and more energyefficient brain of the adult (for review, see Spear, 2000).This adolescent-associated sculpting of brain is highly conserved, with alterationssimilar to those seen in human adolescents also evident during the adolescent9