A follow-up study in the same group of adolescents found that males had significantly greater apparent GM density (aGMD) in the putative cortico-spinal tract, a region containing fibers emanating from Brodman's area 4 and thought likely to be involved in motor control (Herve et al., 2009). Males showed a significant increase in aGMD with age, while females did not, such that the sex differences in volume were only present in older adolescents. Rising levels of bioavailable testosterone in males contributed to the variance in the aGMD even after accounting for age effects; females did not show a similar rise in testosterone levels or a similar relationship to aGMD.
