Rest-activity rhythms and white matter microstructure across the lifespan

The purpose of this study was to examine how rest-activity (RA) rhythm stability may be associated with white matter microstructure across the lifespan in healthy adults free of significant cardiovascular risk. We analyzed multi-shell diffusion tensor images from 103 healthy young and older adults using tract-based spatial statistics (TBSS) to examine relationships between white matter microstructure and RA rhythm stability. RA measures were computed using both cosinor and non-parametric methods derived from seven days of actigraphy data. Fractional anisotropy (FA) and mean diffusivity (MD) were examined in this analysis. Because prior studies have suggested that the corpus callosum (CC) is sensitive to sleep physiology and RA rhythms, we also conducted a focused region of interest analysis on the CC. Results indicated that greater rest-activity rhythm stability was associated with greater FA across both young and older adults, primarily in the corpus callosum and anterior corona radiata. This effect was not moderated by age group. Further, while RA measures were associated with sleep metrics, RA rhythm measures uniquely accounted for the variance in white matter integrity. This study strengthens existing evidence for a relationship between brain white matter structure and RA rhythm stability in the absence of confounding health risk factors. While there are differences in RA stability between young and older adults, the relationship with brain white matter appears to be stable across the lifespan. RA rhythms may be a useful biomarker of brain health across adult development