The Surprising Effects of Exercise on Memory

Neuroscience

By: Amanda White, research technologist in the Department of Psychiatry

Running_Man_Kyle_CassidyNow that winter has descended upon central Pennsylvania, all I want to do is burrow into a pile of blankets and drink tea. But in the weeks ahead, I have to finish up projects, get together with family and friends, write cards, shop for last-minute gifts, and bake 6 different kinds of cookies.

There’s a lot to going on during the holiday season, but exercise may help you keep track of things in ways you might not expect.

Researchers at UC San Diego and the Salk Institute for Biological Studies were among the first to examine the effects of exercise on neurogenesis in the hippocampus—that is, the birth of new neurons in a brain structure critical for learning and memory.

Previous studies had demonstrated that housing rodents with toys and climbing surfaces (“environmental enrichment”) had a positive effect on hippocampal neurogenesis. The researchers had a hunch that, like environmental enrichment, exercise might promote hippocampal neurogenesis.

They found that both environmental enrichment and voluntary exercise (housing mice with running wheels) promoted survival of new neurons in a region of the hippocampus called the dentate gyrus. However, only voluntarily exercising mice had significantly more newborn neurons in this region.

Unsurprisingly, proteins that promote the growth and development of neurons are also boosted following exercise. These neurotrophic factors have also been associated with learning and memory, so van Praag and colleagues followed up on their previous study by investigating the effects of exercise on performance on a common memory task called the Morris water maze task.

morris water mazeIn this task, mice are placed in a large pool of water which contains a platform hidden below the water’s surface; the mice, however, can’t actually see the platform. During the training phase, mice swim around the pool until they locate the platform. They learn to use spatial cues to navigate successfully.

During the testing phase, the platform is removed and researchers record the amount of time mice spend in the region of the pool in which the platform was previously located. The exercised mice took shorter paths and less time to reach the platform, suggesting that they had significantly better spatial memory than controls.

Research also suggests that exercise may alleviate the burden of Alzheimer’s disease and the cognitive decline that occurs with age.

Elderly_exerciseIn both early and late stages in mouse models of Alzheimer’s disease, exercise improves performance on the Morris water maze task and a test of object recognition memory. Epidemiological studies of human populations suggest that individuals who exercise regularly are at a decreased risk of Alzheimer’s disease and other forms of dementia.

In a large multisite study, Erickson and colleagues examined the effects of exercise on hippocampal volume and memory in older adults without dementia. Adults participating in a moderate aerobic exercise program had significantly greater hippocampal volume after a year while those in the control group had experienced a decline in hippocampal volume. Though the authors could not measure hippocampal neurogenesis directly, they found that hippocampal volume was only significantly increased in the dentate gyrus, where adult neurogenesis takes place.

Among members of the aerobic exercise group, increased hippocampal volume was associated with increased performance on a task of spatial memory. Exercise may be protective against the decline in hippocampal volume and cognitive abilities that occurs with Alzheimer’s disease and that occurs with typical aging.

Researchers are still piecing out the details of the relationships between exercise, hippocampal neurogenesis, and memory. However, it is clear that exercise has a strong positive effect on memory.

If you find yourself forgetting where you’ve hidden the Christmas presents, a jog might just jog your memory!

Erickson, K. I., Voss, M. W., Prakash, R. S., Basak, C., et al. (2010). Exercise training increases size of hippocampus and improves memory. PNAS, 108(7), 3017-3022.

Intlekofer, K. A., & Cotman, C. W. (2013). Exercise counteracts declining hippocampal function in aging and Alzheimer’s disease. Neurobiology of Disease, 57, 47-55.

van Praag, H., Christie, B. R., Sejnowski, T. J., & Gage, F. H. (1999). Running enhances neurogenesis, learning, and long-term potentiation in mice. PNAS, 96(23), 13427–13431.

van Praag, H., Kempermann, G., & Gage, F. H. (1999). Running increases cell proliferation and neurogenesis in the adult mouse dentate gyrus. Nature Neuroscience, 2(3), 266-270.

Voss, M. W., Vivar, C., Kramer, A. F., & van Praag, H. (2013). Bridging animal and human models of exercise-induced brain plasticity. Trends in Cognitive Sciences, 17(10), 525-544.

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