and adolescents, higher FA values in the caudate and thalamus were found in boys than in girls (Menzler et al. 2011; Pal et al. 2011), suggesting that sexual dimorphism of anisotropy in the deep GM structures arises after birth. Girls from 5–18 years old displayed a trend toward increased FA with age only in the right hemisphere (arcuate fasciculus, frontal lobe and occipito-temporo-parietal white matter) while boys displayed this trend only in the left hemisphere frontal lobe (Schmithorst et al. 2008). Girls also showed a greater MD increase with age compared with boys in associative regions (Schmithorst et al. 2008). In young adults, men have higher FA than women in the genu and the splenium of the corpus callosum (Westerhausen et al. 2004; Chiang et al. 2011), while women have higher FA in the middle and superior occipital gyri (Chiang et al. 2011). In the genu and splenium of the corpus callosum, the external and internal capsules and the superior fronto-occipital fasciculus, genetic influences account for approximately 80% of the variation in FA in men (Figure 2B) (Chiang et al. 2011). No gender differences in brain structures were found for RD (Perrin et al. 2009; Bava et al. 2011) across
