Impact of Aerobic Fitness on Cerebral White Matter Integrity in the Cingulum.

Abstract

Aerobic fitness may help maintain cognitive function in older adults. However, little is known about the potential mechanisms by which improvements in aerobic fitness may lead to these changes. One potential mechanism is cerebral white matter integrity (CWMI). Both CWMI and aerobic fitness decline with aging. Hence, different aerobic fitness levels may be related to varying amounts of CWMI, which then could impact cognitive function. PURPOSE: To determine brain regions with significant positive associations between CWMI and aerobic fitness in older adults. METHODS: 15 older adults (66 + 6 yrs) completed peak VO2 treadmill testing (Modified Pepper Protocol; VO2 peak range = 14 to 54 ml/kg/min). Magnetic resonance (MR) imaging was used to analyze multiple brain regions during rest on a separate day. Structural 3D T1 MP-Rage and diffusion tensor imaging (DTI, 21 directions, repeated 4x) was done using a 3.0 Tesla MR imaging unit. 3D fractional anisotropy (FA) maps were computed from the raw DTI data. Previous research has shown age-related FA declines in the frontal regions, therefore the specific regions of interest (ROI) identified for this study were the cingulum, genu of the corpus callosum, and uncinate fasciculus (UNC). All ROIs were outlined using InsightSNAP software on the FA maps (FA Coefficient of Variance = 3.9%). RESULTS: Manova revealed no significant age and gender effects. Bivariate analysis showed an overall positive correlation between FA and VO2 peak for the entire cingulum (r = 0.536: p = 0.032). A multiple regression analysis indicated varying contributions of VO2peak on the FA within specific segments of the cingulum (anterior: R2 = 0.32, p = 0.014; medial: R2 = 0.18, p = 0.056; posterior: R2 = 0.04, p = 0.25). Analyses of specific segments within the left and right cingulum resulted in significant correlations between FA and VO2peak in the left anterior (r = 0.559, p = 0.030) and left medial (r = 0.572, p = 0.026) segments. Multiple regression revealed that the greatest unique contribution of VO2peak to the FA variance resided in the medial segment of the left cingulum (R2 = 0.33, p = 0.026 ). Genu and UNC results: r < 0.48; R2 < 0.23, p > 0.07. CONCLUSIONS: There are segment and side-specific positive associations between CWMI and aerobic fitness in the cingulum. Funding: Biomedical Research Imaging Center, UNC-CH.