SAN FRANCISCO — Practice is key to success in any field of athletics. Why? Practice is essential to “locking in” muscle memory. For example, whenever a football quarterback throws a touchdown pass their brain relies heavily on motor memory refined through hours of practice and repetition. Now, researchers from the University of California-San Francisco report that motor memory skills are refined and consolidated during sleep.
As we sleep, researchers say our minds process the day’s lessons to make the physical act of performing newly learned acts subconscious. More specifically, the study finds the human mind achieves this by reviewing the trials and errors of a given action. So, circling back to a hypothetical NFL QB, that would mean weeding out the memory of all throws except those that hit the intended mark. Throws the brain deems “good enough” are then remembered and incorporated into muscle memory. Eventually, the QB will wake up one morning capable of throwing with a high degree of accuracy without actually having to think about the physical movements involved.
“Even elite athletes make errors, and that’s what makes the game interesting,” says Karunesh Ganguly, MD, PhD, a professor of neurology and member of the UCSF Weill Institute for Neurosciences, in a university release. “Motor memory isn’t about perfect performance. It’s about predictable errors and predictable successes. As long as the errors are stable from day to day, the brain says, ‘Let’s just lock this memory in.’”
The sleeping brain focuses on success!
The research team discovered that this neural memory “locking in” process involves surprisingly complex communications between various brain regions, and even occurs during the deep, restorative portion of slumber known as non-REM sleep. Making a poignant observation, Prof. Ganguly adds that the conscious brain often can’t help but fixate on failure – so at least we can focus on our successes during sleep!
“During sleep, the brain is able to sift through all the instances it’s taken in and bring forward the patterns that were successful,” the study author adds.
Scientists once believed that learning motor skills only required the motor cortex. Today, we know it’s a bit more of a complex process. To investigate this topic further, researchers gathered together a group of rats and assigned the rodents a task to reach for pellets. From there, study authors watched the rodents’ brain activity in three regions during NREM sleep: the hippocampus, the region responsible for memory and navigation, the motor cortex, and the prefrontal cortex (PFC).
Over the course of just under two weeks (13 days), a pattern became apparent. To start, in a process called “fast learning,” the PFC coordinated with the hippocampus, probably enabling the rodents to perceive their own motion in relation to the space around themselves and their location in that space. During that stage, the brain appeared to be both exploring and comparing all prior actions and patterns created while practicing that task.
Next, during the “slow learning” process, the PFC appeared to make value judgements, probably largely driven by neural reward centers activated when the task was completed successfully. The PFC engaged in crosstalk with both the motor cortex and the hippocampus and turned down all signals related to failures while turning up signals connected to successes.
Finally, as the electrical activity of the neural regions synchronized, the role of the hippocampus diminished considerably, with instances or events the brain deemed rewarding being stored in what we call “motor memory.”
The brain excuses certain errors while learning skills
As the rodents initially learned their task, their brain signals were noisy and disorganized to start. As more time went on, however, researchers noted the signals began synchronizing until the rats were succeeding about 70 percent of the time. After that marker, the brain appeared to even ignore mistakes and maintain motor memory as long as the level of success was stable. So, in simpler terms, the brain starts to anticipate a certain level of error, thus does not update motor memory.
Just like an elite human athlete, the rats eventually mastered a skill based on a mental model of how the world works, created all by themselves through their own physical experience with gravity, space, and other cues. However, this variety of motor learning can’t be easily applied to different situations in which the cues and physical environment are different.
“If all that changed, for example, if Steph Curry was in the world of Avatar, he might not look as skilled initially,” Prof. Ganguly says.
What if an elite athlete, let’s say Steph Curry, hurt one of his fingers and had to learn to shoot baskets a little differently?
“It’s possible to unlearn a task, but to do that, you have to stress the situation to a point where you’re making mistakes,” Ganguly notes.
When slight changes were made to the rats’ pellet procurement task, the rodents did end up making more mistakes and more noise was seen in the rats’ brain activity. That change was just small enough so that the rats didn’t have to start from scratch, so to speak, only to their “breaking point,” and relearn the task from there.
However, because motor memory becomes ingrained as a set series of motions that follow each other in sequential order, Prof. Ganguly explains changing motor memory in a complex motion like free throwing a basketball may necessitate changing the motion that is used to initiate the entire sequence.
Imagine Steph Curry usually bounces a basketball twice before he throws, Prof. Ganguly adds.
“It might be best to retrain the brain by bouncing it only once, or three times. That way, you’d start with a clean slate.”
The study is published in the journal Nature.