Cognitive activity, cognitive function, and brain diffusion characteristics in old age.

The objective of this work was to test the hypotheses that a) more frequent cognitive activity in late life is associated with higher brain diffusion anisotropy and lower trace of the diffusion tensor, and b) brain diffusion characteristics partially mediate the association of late life cognitive activity with cognition. As part of a longitudinal cohort study, 379 older people without dementia rated their frequency of participation in cognitive activities, completed a battery of cognitive function tests, and underwent diffusion tensor imaging. We used tract-based spatial statistics to test the association between late life cognitive activity and brain diffusion characteristics. Clusters with statistically significant findings defined regions of interest in which we tested the hypothesis that diffusion characteristics partially mediate the association of late life cognitive activity with cognition. More frequent cognitive activity in late life was associated with higher level of global cognition after adjustment for age, sex, education, and indicators of early life cognitive enrichment (p = 0.001). More frequent cognitive activity was also related to higher fractional anisotropy in the left superior and inferior longitudinal fasciculi, left fornix, and corpus callosum, and lower trace in the thalamus (p < 0.05, FWE-corrected). After controlling for fractional anisotropy or trace from these regions, the regression coefficient for the association of late life cognitive activity with cognition was reduced by as much as 26 %. These findings suggest that the association of late life cognitive activity with cognition may be partially mediated by brain diffusion characteristics.