Researchers Show Synchronizing Brain Regions During Sleep To Create Motor Memory
When the Golden State Warriors’ Steph Curry makes a free throw, his brain draws on motor memory. Now researchers at UC San Francisco have shown how this type of memory is consolidated during sleep, when the brain processes the day’s learning to make the physical act of doing something subconscious.
The study, published Dec. 14, 2022, in Nature, shows the brain does this by reviewing the trials and errors of a given action. In the analogy, that means sorting through all the free throws Curry has ever thrown, weeding out the memory of all the actions except those that hit the mark, or that the brain decided were “good enough.” The result is the ability to make the free throw with a high degree of accuracy without having to think about the physical movements involved.
“Even elite athletes makes errors, and that’s what makes the game interesting,” said Karunesh Ganguly, MD, PhD, a professor of neurology and member of the UCSF Weill Institute for Neurosciences. “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.’”
Ganguly and his team found that the “locking in” process involves some surprisingly complex communication between different parts of the brain and takes place during the deep restorative slumber known as non-REM sleep.
Sleep is important because our conscious brains tend to focus on the failures, said Ganguly, who previously identified the sleep-associated brain waves that influence skill retention.
“During sleep, the brain is able to sift through all the instances it’s taken in and bring forward the patterns that were successful,” he said.
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It was once thought that learning motor skills only required the motor cortex. But in recent years a more complex picture has emerged.
To look into this process more closely, Ganguly set rats on a task to reach for pellets. Then, the team looked at their brain activity in three regions during NREM sleep: the hippocampus, which is the region responsible for memory and navigation, the motor cortex and the prefrontal cortex (PFC).
Over the course of 13 days, a pattern emerged.
First, in a process called “fast learning,” the PFC coordinated with the hippocampus, likely enabling the animal to perceive its motion with respect to the space around it and its location in that space. In this phase, the brain seemed to be exploring and comparing all the actions and patterns created while practicing the task.
Second, in a process called slow learning, the PFC appeared to make value judgements, likely driven by reward centers that were activated when the task was successful. It engaged in crosstalk with the motor cortex and the hippocampus, turning down the signals related to failures and turning up the ones related to successes.
Finally, as the electrical activity of the regions became synchronized, the role of the hippocampus diminished and the instances the brain had noted as rewarding came to the fore, where they were stored in what we call “motor memory.”