Sex differences in the gross size of the rat neocortex.

The pervasiveness of sex differences in the size of the rat cerebral cortex was investigated in ten littermate pairs of socially housed Long-Evans hooded rats at 90 days of age. Overall, the cortex was longer and wider in male than in female rats. Sex differences were detected in most cortical regions with this sample size; the exception was the temporal cortex. While some asymmetries were found, they did not vary with the sex of the animal nor were they consistently in one direction. The contribution of the cortical layers to sex differences in cortical thickness was examined in four locations: the primary motor cortex, the forelimb area of the sensorimotor cortex and the monocular and the binocular areas of the visual cortex. The layers that showed sex differences varied among the areas but were confined to layers II-III, V and VI. Sex differences in cortical size were widespread in the adult rat but showed some regional and laminar specificity.