social skills needed for independence, and appropriate adult behavioral repertoires, including becoming leaders and/or followers. The high impulsivity of adolescence likely represents an important risk factor for binge drinking and initiation of drinking experiences(de Wit, 2009). Major changes occur in brain during adolescence with absolute PFC volume declines during adolescence in both humans (Sowell et al., 2001; Sowell et al., 1999) and rats (van Eden et al., 1990). Changes occur in brain regional volumes, chemistry and circuitry. For example, dopamine and serotonin (5-HT) inputs to PFC increase during adolescence to peak levels well above those seen earlier or later in life (Kalsbeek et al., 1988; Rosenberg and Lewis, 1994). Similarly, cholinergic innervation of PFC also increases in adolescence to reach mature levels in both rats (Gould et al., 1991) and humans (Kostovic, 1990). Neuronal circuitry as investigated by stress-induced Fos-like immunoreactivity in cortical and amygdaloid nuclei differs between adolescent and adults (Kellogg et al., 1998; Waters et al., 1997), as do cortisol responses (Walker et al., 2001). Thus, remodeling of the adolescent brain is associated with high impulsivity, high plasticity, and development of more complex adult behaviors.
