Physical Activity Predicts Population-Level Age-Related Differences in Frontal White Matter

Abstract

Physical activity has positive effects on brain health and cognitive function throughout the life span. Thus far, few studies have examined the effects of physical activity on white matter microstructure and psychomotor speed within the same, population-based sample (critical if conclusions are to extend to the wider population). Here, using diffusion tensor imaging and a simple reaction time task within a relatively large population-derived sample (N = 399; 18-87 years) from the Cambridge Centre for Ageing and Neuroscience (Cam-CAN), we demonstrate that physical activity mediates the effect of age on white matter integrity, measured with fractional anisotropy. Higher self-reported daily physical activity was associated with greater preservation of white matter in several frontal tracts, including the genu of corpus callosum, uncinate fasciculus, external capsule, and anterior limb of the internal capsule. We also show that the age-related slowing is mediated by white matter integrity in the genu. Our findings contribute to a growing body of work, suggesting that a physically active lifestyle may protect against age-related structural disconnection and slowing.

Keywords: Brain aging; Cognitive decline; Exercise.

Figure 1

(A) The effect of age on total physical activity energy expenditure (PAEE). (B) The effect of age on PAEE subtypes of home-, work-, leisure-, and commuting-related activities.

Figure 2

(A) The relationship between white matter integrity (fractional anisotropy [FA]) and age (steeper line) and age controlled for PAEE (gentlier line) in genu of corpus callosum (GCC), external capsule (EC), anterior limb of internal capsule (ALIC), and uncinated fasciculus (UNC). FA decreases gradually with age within all of the analyzed white matter tracts: GCC: r = −. 731, p < .001; EC: r = −. 404, p < .001; ALIC: r = −. 218, p < .001; UNC: r = −. 192, p < .001. The detrimental effect of age on FA is diminished in all of the analyzed tracts when PAEE is partialled out from age: GCC: r = −. 688, p < .001; EC: r = −. 348, p < .001; ALIC: r = −. 163, p = .001; UNC: r = −. 130, p = .009. The results indicate a positive relationship between higher physical activity and age-related differences in white matter microstructure. (B) The relationship between reaction time and age (steeper line) and age controlled for white matter integrity (FA) in genu of corpus callosum (gentlier line). Reaction times become gradually slower with age: r = .362, p < .001. The effect of age on reaction time is diminished when FA in genu of the corpus callosum is partialled out from age: r = .156, p = .002. The results indicate a positive relationship between white matter integrity in anterior corpus callosum and age-related differences in reaction time performance. (C) White matter tract ROIs from JHU FA atlas. Tracts which survive the first stage of mediation analysis (genu, anterior limb of the internal capsule, and the external capsule) are rendered in (left to right) superior axial, sagittal, and oblique views. (D) Schematic representation of the mediation paths. PAEE mediates the effect of age on FA in genu of corpus callosum. (E) FA in genu of corpus callosum mediates the effect of age on reaction time. Full color version is available within the online issue.