In girls, estradiol levels were negatively associated with global gray matter volumes and regionally with the inferior frontal gyrus (Peper et al. 2009). In contrast, testosterone levels correlated positively with gray matter volumes in boys (Peper et al. 2009). Testosterone levels also correlated with white matter volumes depending on the androgen receptor (AR) genotype: boys with the more “efficient” (short) AR gene had greater WM volume than those with the less “efficient” (long) AR gene (Figure 2D) (Perrin et al. 2008). Similarly, boys with the more “efficient” AR gene had a less-steep age-related loss in cortical thickness at the inferior parietal lobule. However, girls with the more “efficient” short AR gene had more rapid thinning of the left inferior frontal gyrus (Raznahan et al. 2010 Raznahan et al. 2010). Since the left inferior frontal gyrus is involved in language and impulse-control domains, the more rapid thinning of this brain region suggests earlier maturation in the girls. This longitudinal study of changes cortical thickness in adolescents showed that the AR gene contributes to sexual dimorphism during brain development. Additionally, manipulation of
