Study Shows Sex Differences in Aspects of Brain Anatomy

A scientific analysis of more than 2,000 brain scans found evidence for highly reproducible sex differences in the volume of certain regions in the human brain. This pattern of sex-based differences in brain volume corresponds with patterns of sex-chromosome gene expression observed in postmortem samples from the brain’s cortex, suggesting that sex chromosomes may play a role in the development or maintenance of sex differences in brain anatomy. The study, led by researchers at NIMH, was published in Proceedings of the National Academy of Sciences.

“Developing a clearer understanding of sex differences in human brain organization has great importance for how we think about well-established sex differences in cognition, behavior and risk for psychiatric illness,” said Dr. Armin Raznahan, study co-author and chief of NIMH’s section on developmental neurogenomics. “We were inspired by new findings on sex differences in animal models and wanted to try to close the gap between these animal data and our models of sex differences in the human brain.” 

Researchers have long observed consistent sex-based differences in subcortical brain structures in mice. Some studies have suggested these anatomical differences are largely due to the effects of sex hormones, lending weight to a “gonad-centric” explanation for sex-based differences in brain development. 

However, more recent mouse studies have revealed consistent sex differences in cortical structures as well, and gene-expression data suggest that sex chromosomes may play a role in shaping these anatomical sex differences. Although the mouse brain shares many similarities with the human brain, it is not clear whether these key findings in mice also apply to humans.