Adolescence is associated with continued growth of head size and substantial changes in regional brain structure. Over the last two decades, quantitative cross-sectional studies using structural magnetic resonance imaging (MRI) revealed a curvilinelar developmental trajectory of cortical gray matter with an increase from birth to about 10 years of age followed by a continuous decline through adulthood to old age (Bartzokis et al., 2001; Blanton et al., 2001; Blatter et al., 1995; Caviness et al., 1996; Courchesne et al., 2000; De Bellis et al., 2001; Giedd et al., 1996a; for reviews Giedd et al.; Giedd et al., 1996b; Gogtay et al., 2004; Jernigan et al., 2001; Jernigan and Tallal, 1990; Kennedy et al., 1998; Lange et al., 1997; Paus et al., 1999; Pfefferbaum et al., 1994; Raz, 2004; Raz and Rodrigue, 2006; Reiss et al., 1996; Sowell et al., 1999; Sowell et al., 2002; Stiles and Jernigan; Tisserand et al., 2002). A further theme of these studies was the presence of age-related differences in regional brain volumes, suggesting a posterior-to-anterior developmental order. Verification of these cross-sectional data and speculations required longitudinal study to calculate true developmental trajectories and individual differences by brain region and tissue type (Giedd et al., 1996a).
