Hippocampal Plasticity After Acute Exercise In Older Adults: A Diffusion Tensor Imaging Study

Abstract

PURPOSE: The hippocampus is a critical region for many cognitive and memory processes that experience structural and functional decline with age. Exercise is beneficial for the aging brain and shows preferential benefits for hippocampal volume, activation, and memory-related cognitive processes. However, research thus far has primarily focused on the effects of exercise on long-term volumetric changes in the hippocampus using structural MRI. Critically, microstructural alterations within the hippocampus over short time intervals have been associated with neuroplasticity and cognitive changes that do not alter its volume but are still functionally relevant. It is not yet known, however, if microstructural neuroplasticity occurs in the hippocampus in response to a single session of exercise. METHODS: We used a within subject-design to determine if a 30-minute bout of moderate-intensity aerobic exercise altered bilateral hippocampal diffusion tensor imaging (DTI) measures in healthy older adults (n=30) compared to a seated rest control condition. RESULTS: Following exercise there was significantly lower fractional anisotropy (FA) relative to seated rest within the bilateral hippocampus, and this effect was driven by higher radial diffusivity (Dr). No significant differences in mean diffusivity (MD) or axial diffusivity (Da) were observed. Additionally, cerebral blood flow (CBF) data were obtained in a subset of participants (n=13). Differences in Dr within the bilateral hippocampus were significantly associated with differences in bilateral hippocampal perfusion. CONCLUSIONS: These findings suggest that a single session of exercise can lead to microstructural changes in the hippocampus of healthy older adults, and that these differences may be associated with changes in the extracellular space and glial, synaptic, and dendritic processes within the hippocampus. Repeated microstructural alterations from acute bouts of exercise may accumulate and precede larger volumetric and functional improvements in the hippocampus, a region that is often susceptible to age and pathological-related cognitive decline.