Intensity-dependent effects of voluntary exercise on memory task performance in rats

Abstract: Exercise is known to influence cognitive functioning. However, because protocols vary between experiments, optimal duration, intensity, and frequency of exercise are poorly understood. The current study demonstrates that intensity level plays an important role in determining the effect of exercise on spatial memory. This study examined the effect of varying intensities of voluntary wheel running in 23 Sprague-Dawley rats. Daily measures of intensity were recorded for all rats during three, 30-minute sessions of wheel running prior to the start of the experimental period, and rats were categorized as high intensity or low intensity based on average voluntary running speed. Rats were then individually placed in either an exercise wheel or a small cage designed to promote sedentary behavior for 30 minutes per day, six days per week for five weeks. All rats were then trained and tested in the Morris Water Maze (MWM) to determine spatial memory ability. It was hypothesized that rats that voluntarily ran at higher intensities during the five-week exercise protocol would have better spatial memory in the MWM than rats that voluntarily ran at slower intensities and those that did not run at all. Data support the hypothesis, as rats that ran at high intensity during the experimental period performed better on the probe trial of the MWM. This study extends previous research by demonstrating a specific benefit of long-term high intensity exercise. This finding suggests that voluntary exercise enhances spatial memory ability in an intensity-dependent manner.

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