Brain structure, function, and behavior show independent patterns of sex differences

New research published in Nature Communications demonstrates that men and women exhibit distinct biological differences in their brain structure, function, and behavior, with these patterns showing independent relationships. A team led by researchers Siyuan Liu and Armin Raznahan at the National Institute of Mental Health analyzed data from nearly 1,000 healthy young adults who underwent functional MRI scans while performing seven different cognitive tasks.

The study found widespread sex differences in brain activation across 85% of the cerebral cortex, with functional differences being small to moderate in magnitude. Notably, the spatial patterns of sex differences in brain structure and function did not align, indicating that these phenomena are distinct biological phenomena. Furthermore, an individual's degree of typicality in one domain (such as brain volume or behavior) was unrelated to their typicality in another domain.

The researchers also used machine learning models to predict biological sex based on brain activity, brain volume, and behavioral traits, finding that behavior alone could predict sex with 91% accuracy. However, an individual's sex-typical profile in one domain was not correlated with their profile in another domain. Only a small fraction of individuals exhibited consistently male-typical or female-typical profiles across all measurements.

Finally, the researchers found that variations in brain activation between individuals correlated with variations in behavior within each sex group, but the overall topography of this relationship was broadly consistent across both sexes. Despite the observational nature of the study, these findings underscore the significance of sex differences in brain structure, function, and behavior.