The impact of sex, puberty, and hormones on white matter microstructure in adolescents.

BACKGROUND During adolescence, numerous factors influence the organization of the brain. It is unclear what influence sex and puberty have on white matter microstructure, as well as the role that rapidly increasing sex steroids play. METHODS White matter microstructure was examined in 77 adolescents (ages 10-16) using diffusion tensor imaging. Multiple regression analyses were performed to examine the relationships between fractional anisotropy (FA) and mean diffusivity (MD) and sex, puberty, and their interaction, controlling for age. Follow-up analyses determined if sex steroids predicted microstructural characteristics in sexually dimorphic and pubertal-related white matter regions, as well as in whole brain. RESULTS Boys had higher FA in white matter carrying corticospinal, long-range association, and cortico-subcortical fibers, and lower MD in frontal and temporal white matter compared with girls. Pubertal development was related to higher FA in the insula, while a significant sex-by-puberty interaction was seen in superior frontal white matter. In boys, testosterone predicted white matter integrity in sexually dimorphic regions as well as whole brain FA, whereas estradiol showed a negative relationship with FA in girls. CONCLUSIONS Sex differences and puberty uniquely relate to white matter microstructure in adolescents, which can partially be explained by sex steroids.