Massa Mohamed Ali, HBSc Candidate, University of Toronto
With the end of spring and with summer right around the corner, most of us are getting into outdoor activities that involve biking, swimming, hiking, or playing sports. But why don’t we have to relearn how to perform these activities every summer? Latest research suggests that the answer to this question involves more than just our long-term memory.
Areas of the brain like the sensory motor cortex and the cerebellum are known to be responsible for a lot of the motor skills we have. They coordinate with our muscles, which allows us to remember how to perform certain actions and learn new ones. More specifically, muscle memory is a type of procedural memory. It is considered non-declarative or implicit and includes the long-term memory of actions, routines, and skills. Procedural memory could be knitting, cooking, playing an instrument, dancing, or driving. If you've ever suddenly found yourself arriving home with no recollection of the driving you just did, know that aside from remembering the route, your procedural memory was at play. You probably sped up, slowed down, hit the brakes, turned, and changed lanes without realizing. Even writing is a form of procedural memory. It is not consciously recalled or easily explained - hence the name non-declarative.
Making You More Efficient
With time and practice, these actions can be performed almost automatically because of the strength of the specific neural connection we have made for it in our brains. The more we activate it (could be through visualization or literal performance), the more we strengthen the implicit long-term memory, and the easier it becomes to recall. This allows us to perform at a more efficient level in our daily lives.
A Nature Neuroscience study scanned patients using an MRI before and after six weeks of juggling training. The results reveal that white matter connections between areas of the brain responsible for movement and for vision were significantly higher after learning how to juggle. This indicates a faster, easier, and more efficient way to share information between neuronal connections in the brain, which promotes better fine motor coordination. Therefore, learning a new skill not only changes one's behavior, but also changes their brain by causing changes in gray and white matter, which helps one become better at executing various tasks throughout their day. White matter is composed of myelin, which protects nerve fibers and speeds up the signal transmission between them, while gray matter is the nerve fibers themselves. Practicing sequential actions is one way to improve one's procedural memory, especially when they first learn the action. For instance, you could practice the same song on a musical instrument, or the same route when you're driving until you form a strong long-term memory of the activity.
Changing Your Cells
Even on a muscular level, a Journal of Physiology study suggests that previous strength training promotes the regaining of muscle mass after long periods of inactivity with and without the use of anabolic steroids. While this phenomenon would often be explained by muscle memory, this study's results show that the muscle cells may have a cellular memory residing in the fibers, separate from the brain's connections. This could be due to the increased number of nuclei generated because of the resistance training. Regardless, previous exercise - most notably strength training - is shown to be beneficial later in life. Essentially, any procedural memory you learn will not go to waste but will benefit you - especially in the long-term.
Altering Your DNA
In addition to the separate cellular memory of muscles, some studies suggest a genetic memory in the muscles. A 2021 study published in Function under the American Physiological Society found changes in rodent muscle DNA after 8 weeks of training. Results showed changes in methylation patterns after training, which persisted several months after stopping the regular exercise. These changes also helped trained mice gain more muscle quicker than untrained mice after periods of inactivity, suggesting that the previous training was remembered by muscle cells and DNA. Similarly, a Scientific Reports study on over 850,000 sites of human DNA found that genes in muscles keep track of previous muscle growth, which helps them grow bigger later in life. Following one resistance training session, some of these epigenetic memory changes remained even after 22 weeks of inactivity.
While these results have many implications on athletes, they could also help seniors and concussion patients with recovery. We can use these findings to our advantage in our everyday life by gaining new muscle memories as soon as we can, which will not only help us in the short-term, but in the long-term as well, through improving our bone health, muscle strength, and brain efficiency. The good news is, we should be able to create these memory, cellular, and genetic changes in our brain and muscles at any time and age!
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