EXERCISE ENHANCES ALLOCENTRIC PROCESSING AND HIPPOCAMPAL FUNCTION IN THE ADULT BRAIN

Abstract

This experiment explored whether a long-term aerobic exercise program may induce significant structural and functional changes in the hippocampus, an area of the brain that is important for spatial navigation and memory formation. Based on existing rodent studies, we hypothesize that exercise will cause a shift to allocentric processing, away from a less robust egocentric learning strategy. It is possible that exercise-induced relief of chronic stress, which contributes to improved hippocampal function, will increase reliance on allocentric spatial navigation. Neurogenesis, which occurs in the dentate gyrus region of the hippocampus, is another indicator of hippocampal function that may influence this shift to allocentric learning.

The current study examines whether six weeks of aerobic exercise enhances allocentric processing in healthy young adults. Forty-nine young adults (35 female; age range 18-29 years) were randomly assigned to one of three groups: 1) High intensity interval training group, 2) Moderate intensity training group, or 3) Non-exercising control group. Hippocampus-dependent memory was assessed before and after the intervention on a Virtual Reality Water Maze task, and a high interference memory task, the Mnemonic Similarity Task (MST) which may be dependent on hippocampal neurogenesis. Levels of chronic stress and depression were measured using the Beck Depression Inventory II. It was expected that exercise would improve spatial memory performance on the water maze task, and that performance would improve in proportion to enhanced fitness levels. This improvement in spatial memory performance was expected to correlate with the two indicators of hippocampal function that were assessed in the current study—chronic stress and performance on the high interference memory task.

Six weeks of regular aerobic exercise resulted in a 21.5% improvement in spatial memory performance on the water maze task, indicating improved hippocampus-mediated spatial memory function. Improvements displayed by high intensity exercisers were greater than those observed in the moderate intensity exercisers, suggesting that higher intensity exercise may be more effective in enhancing hippocampal function. Importantly, low responders to exercise exhibited a 30% improvement in water maze performance, suggesting that even minor fitness improvements can lead to significant cognitive gains. Chronic stress and depression, and performance on the MST were not significantly associated with changes in spatial memory performance; however trends observed may offer some explanation to the aforementioned changes in spatial memory. Findings from the current study have important implications for treatment options in populations that are currently, or at risk of suffering from impaired hippocampal function.