Changes in white matter microstructure and MRI-derived cerebral blood flow after 1-week of exercise training

Abstract

Exercise is beneficial for brain health, inducing neuroplasticity and vascular plasticity in the hippocampus, which is possibly mediated by brain-derived neurotrophic factor (BDNF) levels. Here we investigated the short-term effects of exercise, to determine if a 1-week intervention is sufficient to induce brain changes. Fifteen healthy young males completed five supervised exercise training sessions over seven days. This was preceded and followed by a multi-modal magnetic resonance imaging (MRI) scan (diffusion-weighted MRI, perfusion-weighted MRI, dual-calibrated functional MRI) acquired 1 week apart, and blood sampling for BDNF. A diffusion tractography analysis showed, after exercise, a significant reduction relative to baseline in restricted fraction-an axon-specific metric-in the corpus callosum, uncinate fasciculus, and parahippocampal cingulum. A voxel-based approach found an increase in fractional anisotropy and reduction in radial diffusivity symmetrically, in voxels predominantly localised in the corpus callosum. A selective increase in hippocampal blood flow was found following exercise, with no change in vascular reactivity. BDNF levels were not altered. Thus, we demonstrate that 1 week of exercise is sufficient to induce microstructural and vascular brain changes on a group level, independent of BDNF, providing new insight into the temporal dynamics of plasticity, necessary to exploit the therapeutic potential of exercise.

Figure 1

Diffusion MRI analysis showing exercise-induced differences. Top panel shows TBSS results for fractional anisotropy (FA) and radial diffusivity (RD) differences between the pre- and post-exercise intervention scans, clusters are displayed at p < 0.05, FWE-corrected (TFCE) and fattened with the “tbss_fill” script for the purpose of better visualization, shown against the the mean FA fibre skeleton (green) and overlaid on the FMRIB FA 1 mm template. Red represents a significant increase in values (post > pre) and blue represents a decrease (post < pre). Bottom panel shows representative tract segmentations for the corpus callosum (genu [red], body [green], splenium [purple]), uncinate fasciculus (yellow), fornix (pink), and parahippocampal cingulum (PHC; green), overlaid on the FA map. Graph shows the partial residual plot from the linear mixed effect model, showing the effect of exercise on restricted fraction (FR), with the effects of all the control variables accounted for, with error bars representing 95% confidence intervals and individual data points. The raw tractography FR data is graphically represented in Supplementary Fig. 5.

Figure 2

Study design. Brain-derived neurotrophic factor (BDNF) refers to the collection and sampling of blood serum for BDNF levels. For the fitness test, BDNF was sampled before and after the test. MRI magnetic resonance imaging.