Sex differences in the development of learning abilities in primates.

The role of steroid gonadal hormones in promoting sex differences in reproductive behaviors has been thoroughly studied in numerous mammalian species. More recent experiments have indicated that the presence or absence of steroid hormones during the critical period of brain differentiation likewise might promote the development of sex differences in cognitive abilities. Studies in infant rhesus monkeys have demonstrated that there exist sex differences in learning abilities that can be altered by perinatal hormonal manipulations, suggesting that testosterone might be a crucial factor responsible for the development of sex differences in cognitive styles. In addition, neonatal lesion studies have shown that the cortical areas mediating specific learning abilities mature at different rates in male and female infant monkeys. These findings support the view that the perinatal hormonal environment can affect the rate of brain maturation by influencing neuronal connectivity at the cortical level. The combined data from sex differences in learning abilities in human infants and their reversibility in endocrinological syndromes suggest that testosterone may affect the maturation of the human brain in a manner similar to that demonstrated in nonhuman primates.