Muscle memory is fascinating to me. Humans can perform complex processes with very little cognitive awareness regarding specific movements taken. How does it work?
For example, I’m a guitar player. When I play a complex legato run or a particularly challenging chord progression, despite it being fairly advanced, I’m not thinking to myself “alright, I’m going to place my first finger on the 1st fret of the E string, 3rd finger 3rd fret of the A string…”. It doesn’t work like that. I just kind of pick up my guitar and play it without really putting much thought in to it. Sometimes when I’m playing something really difficult, it feels automatic and robotic, like I’m not even playing it. Just watching someone do it.
Similarly, any changed variables can completely throw me off; a difference in the string gage, string tension, scale length. Once it becomes dissimilar, I have to take a step back and actually *think* about what I’m doing because the muscle memory fails me. Despite me knowing in my head exactly what to play, my fingers just don’t seem to cooperate because the environment is so different than what I’m used to.
In: Biology
One thing to keep in mind, is that conscious thought is only part of the brain’s many jobs, and quite a bunch of the stuff in your brain is devoted to automatic stuff your body does without you knowing it. Heart beating, breathing, digestion, all that stuff. There’s also an area which coordinates a lot of your voluntary motor control – the muscle movements which *are* under your control, like playing a guitar.
One cool thing about our brain architecture is that it seems to like to make shortcuts. When it has to do something repeatedly, it tends to form special “shortcut” connections to skip a bunch of intermediate steps. This can happen in our cognition, in our sense perceptions, and in our motor skills alike. So when the cerebellum has to command the same combinations of muscle movements in a repetitive way, in the same order again and again, it may form some neural pathways which automate that combination of motor commands and accomplish it in fewer steps.
The other cool thing is that there is neural tissue distributed all through our bodies, responsible for carrying the messages back and forth, made of a similar type of cell to the stuff in our brains. It takes some time for signals to traverse these nerve fibers, so there’s a limit to how quickly you can respond with your body to what your senses are telling you. But amazingly, these nerve fibers are capable of that same shortcut-forming trick that your brain is, which means that *some* very rudimentary decision-making can be “outsourced” entirely outside the brain!
One example of this is pain reflexes. If you accidentally put your hand on a hot stove, there’s a good chance you’ll jerk your hand away *faster* than would seem possible, given the amount of time it takes your brain and your hand to send messages back and forth. This is possible because the decision to jerk your hand back was made outside your brain – by your nervous system, your spinal cord and the nerve fibers in your arm.
Other repetitive physical behaviours, like sports or dance moves, playing musical instruments, things like that, can also, with time and repetition, be ‘outsourced’ to your nervous system.
When people talk about muscle memory, they’re talking about some combination of these, our brain’s ability to automate complex procedures so they don’t occupy our conscious thought anymore, and this ability for procedural knowledge to be embodied outside the brain in our our nervous system. Most of the time, a lot more of the former than the latter.
It’s not a conscious kind of memory, that’s why it feels weird to your conscious mind. But other than that (and some specifics about brain structure), it’s just a memory.
There are, broadly, two kinds of memory at work for this question: declarative memory and procedural memory. Declarative memory are memories that you can “declare,” such as “I remember my birthday is ….” or “The 27th president of the US was.”
Procedural memories are memories of patterns. Walking home can become a procedural memory: each step is just one in a series of steps that lead you home. It’s a procedure. Playing a song is a procedure, too.
Both kinds of memory are just memories. The biggest thing that feels different about them is that they’re sub-conscious. Your brain has a lot more to it than the conscious part. Your non-conscious brain controls your heart, your blood pressure, your breathing (until you become aware of it). Your non-conscious mind can even answer questions you’ve been stuck on: ever suddenly be struck by inspiration and realize the answer to something out of nowhere? Your subconscious brain was doing the work.
Procedural memory feels different only because it’s subconscious. Since it’s just a kind of memory, it isn’t very flexible. Changing the circumstances of the procedure confuses it. When this happens, your subconscious brain sends an alert to the conscious bit, which is what you experience as surprise.
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