The adolescent brain undergoes dramatic changes in gross morphology. Human structural imaging studies have demonstrated that throughout the cerebral cortex there is a loss of gray matter during adolescence, with gray-matter reductions in portions of the temporal lobe and dorsolateral PFC occurring in late adolescence (Gogtay et al., 2004; Sowell et al., 2003; Sowell et al., 2001; Sowell et al., 2002). Gray matter reductions are also apparent in the striatum and other subcortical structures (Sowell et al., 1999; Sowell et al., 2002). These changes may be related to a massive pruning of synapses observed during this period from animal studies (Rakic et al., 1986; Rakic et al., 1994), although some question this connection as synaptic boutons make up only a small proportion of cortical volume (Paus et al., 2008). Human imaging has also revealed that white matter increase through adolescence in cortical and subcortical fiber tracts (Asato et al., 2010; Benes et al., 1994; Paus et al., 2001; Paus et al., 1999), resulting from increased myelination, axon caliber, or both (Paus, 2010). Changes in the patterns of connectivity also occur
