Physical Activity and Hippocampal Sub-Region Structure in Older Adults with Memory Complaints

BACKGROUND: Physical activity (PA) plays a major role in maintaining cognition in older adults. PA has been shown to be correlated with total hippocampal volume, a memory-critical region within the medial temporal lobe (MTL). However, research on associations between PA and MTL sub-region integrity is limited. OBJECTIVE: To examine the relationship between PA, MTL thickness, and its sub-regions, and cognitive function in non-demented older adults with memory complaints. METHODS: Twenty-nine subjects aged ≥60 years, with memory complaints were recruited for this cross-sectional study. PA was tracked for 7 days using accelerometers, and average number of steps/day determined. Subjects were categorized into two groups: those who walked ≤4000 steps/day (lower PA) and those with >4000 steps/day (higher PA). Subjects received neuropsychological testing and 3T MRI scans. Nonparametric ANCOVAs controlling for age examined differences between the two groups. RESULTS: Twenty-six subjects aged 72.7(8.1) years completed the study. The higher PA group (n=13) had thicker fusiform gyrus (median difference=0.11mm, effect size (ES)=1.43, p=0.001) and parahippocampal cortex (median difference=0.12mm, ES=0.93, p=0.04) compared to the lower PA group. The higher PA group also exhibited superior performance in attention and information-processing speed (median difference=0.90, ES=1.61, p=0.003) and executive functioning (median difference=0.97, ES=1.24, p=0.05). Memory recall was not significantly different between the two groups. CONCLUSION: Older non-demented individuals complaining of memory loss who walked>4000 steps each day had thicker MTL sub-regions and better cognitive functioning than those who walked ≤4000 steps. Future studies should include longitudinal analyses and explore mechanisms mediating hippocampal related atrophy.