Predicting Age-Related Decline in Processing Speed and Executive Functioning: An MRI Study of White Matter Integrity

Normal aging is associated with changes in white matter (WM) integrity including visible lesions such as white matter hyperintensities (WMH) as well as microstructural changes in normal appearing WM (NAWM) measured with diffusion tensor imaging (DTI). Research suggests that WMH and microstructural changes in NAWM may provide independent but complementary information on WM integrity. Reductions in WM integrity and advanced age are also associated with reductions in executive functioning (EF) and processing speed (PS); however, the relationship between WM change and cognition in older adults over time is not fully understood. It is also important to consider other factors that may moderate change in cognition over time, such as intellectual functioning and vascular risk factors. The current study examined how demographics and change in WM integrity predict change on measures of executive functioning and processing speed in a 4-year longitudinal study with a normal aging sample. Eighty-five adults between the ages of 75 and 89 participated in baseline neuropsychological testing. Sixty-four remained at 2 years and 37 remained at 4 years. Multilevel Modeling was conducted to examine how change in WM integrity predicted change on the cognitive measures over and above predictive utility of between-subjects effects. The present study provides support for the hypothesis that reduction in WM integrity predicts cognitive decline in typical aging. Additionally, WMH burden and microstructural indices of WM integrity in NAWM provide non-overlapping but complementary information on how change in WM integrity predicts cognitive decline. Finally, we found evidence that cognitive reserve reflects both the persistence of earlier differences in cognitive functioning in some cognitive domains and the differential rates of decline in other domains. These findings underscore the importance of longitudinal studies in evaluating the role of WM integrity and demographic factors in shaping trajectories of cognitive aging