The prevalence and timing of these and other maturational changes in adolescent brain are regionally specific (and in some cases, sex-specific) (e.g. Lenroot & Giedd, 2006; Lenroot et al., 2007). Such regional differences can be seen at a number of levels, ranging from molecular changes evident only in invasive studies of laboratory animals to age-related changes in relative brain volumes, gray-matter volumes, and ratios of white/gray matter that are widely evident during adolescence across species. For instance, in human imaging studies, developmental declines in gray matter have been shown to occur earlier in sensory and motor regions of the cortex than in prefrontal cortex (PFC) and other cortical association areas thought to play critical roles in impulse control, response suppression, and other cognitive control functions that fall under the rubric of “executive functions” and whose development is prolonged into late adolescence and beyond (Gogtay et al., 2004; Lenroot & Giedd, 2006; Østby et al., 2009; see Casey et al., 2008, and Zucker et al., 2011, for reviews).
