Getting off-tract: Correlational tractography of white matter integrity and cognitive intraindividual variability in a large sample of community-dwelling older adults.

Objective

Cognitive intraindividual variability (IIV), or the dispersion across neuropsychological task performance, is a sensitive marker of neurocognitive aging, but its tract-specific white matter correlates are not well characterized. This study used correlational tractography to identify pathways whose microstructural integrity relates to IIV in older adults.

Method

Participants were a diverse sample of 510 community-dwelling older adults (Mage = 66.6 years, SDage = 8.4) from the Health and Aging Brain Study-Health Disparities cohort. IIV was computed as the intraindividual standard deviation of demographically normed performance T scores across a multidomain battery. Diffusion MRI connectometry in DSI Studio tested partial Spearman associations between IIV and quantitative anisotropy, adjusting for sex and intracranial volume, with permutation testing and false discovery rate adjustment (0.01).

Results

Higher IIV was associated with lower quantitative anisotropy primarily in commissural corpus callosum, fronto-subcortical, and interhemispheric long-range connection fibers. Tracts of the forceps minor were the most robust to sensitivity analyses. Effects were small in magnitude, with the primary connectometry threshold corresponding to an effect size of 0.09, but spatially specific, accounting for 7.57% of total whole-brain tract volume.

Conclusions

Overall, we found that IIV maps onto distributed, tract-specific differences in white matter microstructure. Findings support IIV as a marker linked to structural network-level white matter integrity and should motivate longitudinal work to further clarify its neuroanatomical substrates. (PsycInfo Database Record (c) 2026 APA, all rights reserved).