Your brain’s constant calculations for consistency in movement
The term “muscle memory” really isn’t fair to your cerebellum. However trained and practiced you may be at a certain movement, the coordinating cognition is all thanks to your brain. Not only does your brain learn how a specific movement should be performed, it also constantly runs checks on your performance of those tasks as a sort of “quality control.” It’s been found to be a dynamic system, where your cerebellum is processing feedback in real time in order to keep your steps, throws and pokes as consistent as possible. Until they need to change.
Setting a standard
As you perform a task, feedback about your movements is sent to your cerebellum, where it’s added to a sort of record of how that movement is performed. The more you practice, the more a baseline version of that movement is established. As you learn to do something a specific way, your cerebellum can then start checking on how closely each repetition of that movement matches the expected movement, and then make adjustments.
At the center of these adjustments are what are called sensory prediction errors. Imagine you’re going to pick up a cup, and you reach out your hand. Your cerebellum has an expectation of what feedback you’ll get from your fingers and arm once the cup has successfully be grasped, such as how far your arm as extended, the feeling of the glass, etc. This expectation is then checked against what feedback is actually coming from your arm and hand as you reach out. If there are discrepancies, possibly due to the glass being in a slightly different location, or more tiredness in your muscles, they are used to make on-the-fly changes to your movement. This continues constantly so that the gap between your brain’s model for movement and the actual event is minimized. The more practice you have, the more reliable your cerebellum’s model should be.
Reestablishing your expectations
Of course, the world sometimes changes in larger ways. The gap between expectations and feedback may persist enough that the baseline version of a movement can’t be recreated, in which case your brain updates it’s expectations. This dynamic of rechecking and relearning a movement is actually always in play, with the “normal” version of a movement being updated on a regular basis. This is why practice is so important to any activity, as it allows you to not only strengthen your muscles as necessary, but also manipulate your internal model of what the movement should feel like.
While this activity has been observed down to a single neuron in the cerebellum, we’re not yet able to reproduce it artificially. Experiments involved basic motions, such as a subject turning their head to the left, and then observing how brain activity changed in response to that movement being impeded slightly, requiring an adjustment in muscle activity. If these calculations in the cerebellum are ever reverse-engineered, it may be helpful in treating patients with damage to their cerebellums, such as stroke victims who cannot control their movements well.
Source: How Does a Gymnast, or Even a Fitness Walker, Keep from Falling? by Gary Stix, Talking Back
