Is Memory Linked to Muscle Memory?

Most of us are familiar with the concept of “muscle memory.” For musicians learning how to play a song or injured athletes who need to re-train, the repeated patterns and procedures learned by our muscles help. The muscles in our fingers remember how to play a song on the piano, and an athlete’s muscles store memories to help him get back into training again. We also know that regular exercise and fitness improves memory. But until recently, scientists weren’t exactly sure how that happens.

A team of scientists at the National Institute on Aging, led by investigator Henriette van Praag, set out to discover exactly what substances, produced by exercising, are effective in the improvement of memory. They ended up zeroing in on the production of a substance called cathepsin B. They found that mice who used their exercise wheels often for a 2-4 week period had higher levels of cathepsin B in their blood than those who did not. They also found that the mice with high cathepsin B levels performed better on memory tasks.

They divided the mice into two groups: those that had been exercising, and those that hadn’t. Both groups were placed in a Morris pool – a small pool in which they have to learn how to swim to a hidden platform. All the mice in the group learned how to swim the platform, but only the mice with elevated levels of cathepsin B remembered how to do so when they were put in the pool the second time.

After making these discoveries about mice, it was time to find out whether the same results would be achieved with other animals. So the researchers tried a similar experiment with monkeys and discovered that their memory also was improved when cathepsin B levels were raised. Now it was time to see how this worked with humans.

For this test, the researchers focused on a group of college students who had sedentary lifestyles, with very little exercise. Half of these students were put on a strict exercise regimen for four months, and became very fit while the other half remained sedentary. The students were then given a memory task in which those who had exercised performed much better than those who did not. The physically active students showed elevated blood levels of cathepsin B and increased neurogenesis of growth cells in the hippocampi.

The implications of this research are that exercise directly aids our memory in a specific manner that we do not yet fully understand. Although it’s clear that an elevated level of cathepsin B improves memory, it is also present in patients with Alzheimer’s and some kinds of cancer. High levels of cathepsin B also occur during cell death due to brain injury. Because of these links, researchers are doubtful about the benefits of artificially raising cathepsin B levels. Exercise is a harmless and natural way to do so, but many patients that are at-risk for Alzheimer’s are not physically able to engage in an exercise regimen.

For the moment, one message is clear. If we want to improve our memory, we need to get off the couch and go exercise whenever we can.

References

  • Hamilton, Jon. “A Protein That Moves From Muscle To Brain May Tie Exercise To Memory.” http://www.npr.org/sections/health-shots/2016/06/23/483245084/a-protein-that-moves-from-muscle-to-brain-may-tie-exercise-to-memory.
  • Williams, Ruth. “Exercise-Induced Muscle Factor Promotes Memory.” The Scientist http://www.the-scientist.com/?articles.view/articleNo/46397/title/Exercise-Induced-Muscle-Factor-Promotes-Memory/
  • Cell Press. “Running releases protein associated with improved memory in mice.” ScienceDaily. https://www.sciencedaily.com/releases/2016/06/160623122940.htm

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