EXPLORING SEX DIFFERENCES IN THE BRAIN ANATOMY OF RHESUS MACAQUES

Sex differences in human brain anatomy and sex bias in the prevalence of certain clinical disorders are well-documented. Specifically, males generally exhibit larger total brain volume (TBV) than females, a difference that remains significant after accounting for body size, while some disorders show sex-biased frequencies, such as the higher prevalence of autism in males and depression in females. Additionally, despite their importance as a translational model in neuroscience, sex-specific differences in rhesus macaque brain anatomy remain relatively underexplored. We addressed this gap by analyzing structural magnetic resonance images from 54 rhesus macaques (17 females, 37 males).
First, we adapted the Multi-Modal Registration Framework (MMORF), originally developed for human neuroimaging, to generate a group-specific template for examining anatomical differences. Preliminary analyses indicate that males have a significantly larger TBV than females, with body weight accounting for only a portion of the observed variance. Regional analyses of absolute volumes further revealed larger male volumes across grey matter, cerebellar, and subcortical regions, including the amygdala, hippocampus, and thalamus, whereas ventricular volumes did not show this pattern.
To contextualize these findings, we compared our results to reported sex-specific patterns in mice and humans. In our previous work in mice, similar sex biases were observed across most regions, apart from a female bias in the cerebellum, a pattern not observed here in macaques. These findings provide an initial characterization of sex differences in macaque brain anatomy and demonstrate the importance of including sex as a biological variable when studying sex-biased disorders in translational research.