Dump the "dimorphism": Comprehensive synthesis of human brain studies reveals few male-female differences beyond size
- PMID: 33621637
- DOI: 10.1016/j.neubiorev.2021.02.026
Dump the "dimorphism": Comprehensive synthesis of human brain studies reveals few male-female differences beyond size
Abstract
With the explosion of neuroimaging, differences between male and female brains have been exhaustively analyzed. Here we synthesize three decades of human MRI and postmortem data, emphasizing meta-analyses and other large studies, which collectively reveal few reliable sex/gender differences and a history of unreplicated claims. Males' brains are larger than females' from birth, stabilizing around 11 % in adults. This size difference accounts for other reproducible findings: higher white/gray matter ratio, intra- versus interhemispheric connectivity, and regional cortical and subcortical volumes in males. But when structural and lateralization differences are present independent of size, sex/gender explains only about 1% of total variance. Connectome differences and multivariate sex/gender prediction are largely based on brain size, and perform poorly across diverse populations. Task-based fMRI has especially failed to find reproducible activation differences between men and women in verbal, spatial or emotion processing due to high rates of false discovery. Overall, male/female brain differences appear trivial and population-specific. The human brain is not "sexually dimorphic."
Keywords: Amygdala; Anterior commissure; Connectome; Corpus callosum; Cortical thickness; Default mode network; Emotion; Empathy; Gender; Hippocampus; Lateralization; MRI; Massa intermedia; Mental rotation; Meta-analysis; Multivariate; Precision medicine; Sex; Spatial; Verbal.
Copyright © 2021 The Author(s). Published by Elsevier Ltd.. All rights reserved.
Comment in
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Sex differences in the human brain: a roadmap for more careful analysis and interpretation of a biological reality.Biol Sex Differ. 2022 Jul 26;13(1):43. doi: 10.1186/s13293-022-00448-w. Biol Sex Differ. 2022. PMID: 35883159 Free PMC article. Review.
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