SEXUAL DIMORPHISM OF THE DEVELOPING HUMAN BRAIN

1. Sexual dimorphism of human brain anatomy has not been well-studied between 4 and 18 years of age, a time of emerging sex differences in b ehavior and the sexually specific hormonal changes of adrenarche (the predominantly androgenic augmentation of adrenal cortex function occur ring at approximately age 8) and puberty. 2. To assess sex differences in brain structures during this developmental period volumes of the c erebrum, lateral ventricles, caudate, putamen, globus pallidus tempora l lobe, amygdala, and hippocampus, and midsagittal area measurements o f the corpus callosum were quantified from brain magnetic resonance im ages of 121 healthy children and adolescent and examined in relation t o age and sex. 3. Males had a 9% larger cerebral volume. When adjusted for cerebral volume by ANCOVA only the basal ganglia demonstrated sex differences in mean volume with the caudate being relatively larger i n females and the globus pallidus being relatively larger in males. Th e lateral Ventricles demonstrated a prominent sex difference in brain maturation with robust increases in size in males only. A piecewise-li near model revealed a significant change in the linear regression slop e of lateral ventricular volume in males after age 11 that was not sha red by females at that or other ages. 4. Amygdala and hippocampal volu me increased for both sexes but with the amygdala increasing significa ntly more in males than females and hippocampal volume increasing more in females. 5. These sexually dimorphic patterns of brain development may be related to the observed sex differences in age of onset, preva lence, and symptomatology seen in nearly all neuropsychiatric disorder s of childhood.