Given the remarkable heterogeneity in the lobar GM development, it became important to study GM development at functionally distinct sub-regional levels. This was achieved in the subsequent studies using finer-scale GM mapping methods. These studies confirmed the maturation related loss of cortical GM density over time across the entire age span, with rapid attrition of frontal lobe gray matter in late adolescence (E. R. Sowell et al., 2003; E. R. Sowell, Thompson, Holmes, Jernigan, & Toga, 1999). When these techniques were applied to longitudinal samples, the first dynamic maps of gray matter maturation were created. In the pre- and post- pubertal period, individual sub-regions followed temporally distinct maturational trajectories. Typically, the primary sensorimotor cortices and the frontal and occipital poles matured first, and the remainder of the cortex developed in a parietal to frontal (back-to-front) direction. The superior temporal cortex, which contains association areas that integrate information from several sensory modalities, matured last suggesting that the higher-order association areas mature only after the lower-order sensorimotor regions, whose functions they integrate, have matured (Gogtay, Giedd et al., 2004). Time-lapse maps of
