Neurite Orientation Dispersion Density Imaging Indicates Positive Associations Between Physical Activity And White Matter Structure

Human and animal studies have shown that exercise training increases hippocampal volume and improves cognitive function, but whether exercise influences white matter (WM) microstructure in healthy women is not fully understood. PURPOSE: To compare cerebral WM microstructure between high and low active women. METHODS: Forty-eight healthy women (ages 25-40) who reported either greater than 300 minutes per week of moderate-vigorous physical activity (MVPA) from exercise training, designated as high active (HA; n = 31)) or less than 30 minutes of MVPA, designated as low active (LA; n = 17), were enrolled. Physical activity was measured over 14 days using accelerometry. WM integrity was assessed using diffusion-weighted Magnetic Resonance Imaging that included Diffusion Tensor Imaging (DTI) and Neurite Orientation Dispersion and Density Imaging (NODDI). A multiple b-value diffusion weighted EPI sequence was used to acquire a total of 126 diffusion weighted images, plus 10 images without additional diffusion weighting. This included 18 images with b = 350 s/mm2, 36 with b = 800 s/mm2, and 72 with b = 2000 s/mm2. Tract-based Spatial Statistics were used to estimate WM DTI and NODDI metrics over the whole brain corrected using a threshold-free cluster enhancement and a family-wise error correction for multiple comparisons at the p < 0.05 level with 5000 permutations. Analysis of Covariance was used to compare groups on each DTI variable of interest covarying for age. Multiple linear regression was used to test the associations between sedentary time, DTI, and NODDI measures. RESULTS: HA women had higher fractional anisotropy (FA), lower radial diffusivity (RD), and lower orientation dispersion index (p ≤ 0.05) in the corpus callosum – consistent with higher WM integrity. For the whole sample, higher levels of sedentary behavior were negatively associated with FA and neurite density index and positively associated with RD across extensive white matter areas (p ≤ 0.05) – consistent with lower WM integrity. CONCLUSION: Performing high levels of physical activity and spending less time in sedentary behavior may benefit white matter microstructure in tracts involved in a diverse array of cognitive, emotional, motor, and perceptual functions. Supported by a grant from the Virginia Horne-Henry Foundation.