Gender differences in the human cerebral cortex: More neurons in males; More processes in females

This study's objective was to investigate morphometric gender differences o f the cerebral cortex in six males and five females, 12 to 24 years old. Th ough human brains lack sexual dimorphism on routine neuropathologic examina tions, gender-specific brain weight, functional, and morphologic difference s exist, suggesting that cortical differences may be found. Yet the cerebra l cortex may be exempt from gender differences, as demonstrated by the fact that normal males and females perform comparably on intelligence tests. St ereologic morphometry on standardized histologic sections from 30 bilateral cortical loci determined cortical thickness, neuronal density, and derived neuronal number estimates. The mean +/- SD cortical thickness of the 60 lo ci examined was similar in males and females with right and left hemispheri c gender ratios being balanced. In contrast, the average neuronal density o f the same 60 loci was significantly higher in the male group than in the f emale group, and the corresponding mean male-to-female ratios were 1.18 in the right and 1.13 in the left hemisphere, which differ significantly from each other and from the balanced cortical thickness ratios. Estimates of ne uronal numbers - the product of neuronal thickness times density - were 13% higher in males than in females, with mean male-to-female ratios of 1.13 i n both hemispheres. The data provide morphologic evidence of considerable c erebral cortical dimorphism with the demonstration of significantly higher neuronal densities and neuronal number estimates in males, though with simi lar mean cortical thickness, implying a reciprocal increase in neuropil/neu ronal processes in the female cortex.