# Ethnic and Sex Differences of White Matter Tracts in Aging

## TL;DR

This study finds that sex influences white matter structure in older adults, while ethnic differences are less clear, with both factors affecting brain aging independently of cognitive status.

## Contribution

The study provides new insights into sex-based differences in white matter microstructure in aging, using FW-corrected FA and detailed callosal segmentation.

## Key findings

- Females had larger normalized corpus callosum volumes in posterior, mid-anterior, and anterior regions.
- Females showed higher fwcFA in the inferior temporal gyrus, while Hispanics had higher fwcFA in the premotor cortex.
- The effects of sex and ethnicity on white matter were small, suggesting other factors may play a larger role in aging.

## Abstract

Research on gender and ethnic differences in white matter tracts yields mixed results. Although men show larger global corpus callosum (CC) in absolute values, women have demonstrated larger splenium and isthmus. Additionally, men have shown greater white matter and fractional anisotropy (FA) in multiple regions than women. This study investigates sex and ethnic differences in the corpus callosum and transcallosal white matter tissue microstructure of older individuals with normal cognition and memory disorders.

191 participants (Female n = 120; Hispanics n = 115; Non‐Hispanics n = 76; Age mean = 71.07; SD = 7.75) were included in the sample from the 1Florida ADRC with cognitively normal (n = 75), MCI (n = 88), and dementia (n = 28) diagnoses. Corpus callosum volumes were collected using a Siemens Skyra 3T MRI scanner and were divided into anterior, mid‐anterior, central, mid‐posterior, and posterior regions. Also, MRI‐based free water diffusion tensor imaging (FW‐DTI) measured FW‐corrected FA (fwcFA) to assess and compare the integrity of transcallosal tract templates (TCATT) across motor, temporal, parietal, and occipital regions across males and females and ethnic groups.

Univariate ANCOVAs controlling for age and clinical diagnosis were performed; females had larger normalized CC volumes in the posterior, F(1, 184) = 8.92, p = .003, ηp
2
 = .046, mid‐anterior, F(1,184)= 5.68, p = .018, η
p
2 = .030, and anterior, F(1,184)= 14.54, p < .001, η
p
2 = .073, regions, which all survived FDR corrections, with no ethnic differences observed. For transcallosal tracts, females had higher fwcFA in the inferior temporal gyrus, η
p
2 Hispanics had higher fwcFA in the premotor cortex, η
p
2
η
p
2

Sex and ethnicity influence white matter changes during aging independently of age and cognitive diagnosis. However, the effect explained by these demographic variables was very small, suggesting the influence of additional factors.