Abstract
Sex differences in the human brain are of interest for many reasons: for example, there are sex differences in the observed prevalence of psychiatric disorders and in some psychological traits that brain differences might help to explain. We report the largest single-sample study of structural and functional sex differences in the human brain (2750 female, 2466 male participants; mean age 61.7 years, range 44–77 years). Males had higher raw volumes, raw surface areas, and white matter fractional anisotropy; females had higher raw cortical thickness and higher white matter tract complexity. There was considerable distributional overlap between the sexes. Subregional differences were not fully attributable to differences in total volume, total surface area, mean cortical thickness, or height. There was generally greater male variance across the raw structural measures. Functional connectome organization showed stronger connectivity for males in unimodal sensorimotor cortices, and stronger connectivity for females in the default mode network. This large-scale study provides a foundation for attempts to understand the causes and consequences of sex differences in adult brain structure and function.
Highlights
Sex differences have been of enduring biological interest (Darwin 1871), but our knowledge about their relevance to the human brain is surprisingly sparse
This was confirmed by computing shift functions (Rousselet et al 2017) for each overall and subcortical brain structure, illustrated in Figure S2a for the raw values and Figure S2b for the values corrected for total brain volume (TBV)
We first tested for mean sex differences in overall cortical and subcortical brain volumes, adjusting each measure for age and ethnicity
Summary
Sex differences have been of enduring biological interest (Darwin 1871), but our knowledge about their relevance to the human brain is surprisingly sparse. It has been noted by several researchers that the potential influences of sex are underexplored in neuroscientific research (Beery and Zucker 2011; Cahill 2006, 2017; Karp et al 2017). Rates of Alzheimer’s disease are higher in females than males, prompting a recent call for the prioritization of biomedical research into sex differences in measures relevant to this disorder (Mazure and Swendsen 2016). Improving therapeutic strategies for these conditions will almost certainly require accurate quantitative estimates of where and how the sexes differ normatively
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