Both grey matter volume decreases and FA increases in frontoparietal regions occur well into adolescence, suggesting a close spatiotemporal relationship (Gogtay et al. 2004; Lebel et al. 2008). Changes in tissue morphometry are attributable to synaptic proliferation and pruning (Huttenlocher 1979) as well as myelination. Diminutions in gray matter density and concomitant brain growth in dorsal parietal and frontal regions suggest an interplay between regressive and progressive changes (Sowell et al. 2001), and the coupling of these neurobiological processes is associated with increasingly economical neural activity (Huttenlocher and Dabholkar 1997).
