Effects of sex and age on presumed inhibitory interactions in 6 areas of the human cerebral cortex as revealed by the fMRI Human Connectome Project.

Cortical inhibition is theorized to reflect an underlying property of human brain function, sharpening tuning and shaping connectivity. Although age and sex effects on large-scale resting-state brain connectivity have been well documented, effects on local cortical inhibition have received relatively limited attention. Here, we evaluated age and sex effects on presumed local inhibitory interactions in 6 lateral cortical areas using resting-state functional magnetic resonance imaging (fMRI) data acquired from 1054 young adults who participated in the Human Connectome Project. For each area, all possible pairwise crosscorrelations between prewhitened blood oxygenation level-dependent (BOLD) time series were calculated, and the highest value (CCmax) was retained to determine the mean and percentage of negative and positive CCmax. Here, we focused on the percentage of negative CCmax which we referred to as presumed "percent inhibition". The results documented regional differences in percent inhibition as well as age and sex effects, such that women's brains were characterized by significantly higher percent inhibition than men overall and in 4 of the 6 cortical areas, and the percent inhibition increased significantly with age in all 6 areas for women but in only one area for men. The findings from this young adult sample are presumed to reflect ongoing maturational processes involving local network connectivity that may be shaped by sex differences in brain structure, function, and neurochemistry.