Researchers show how motor memory is consolidated during sleep

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When Steph Curry of the Golden State Warriors makes a free throw, his brain turns to motor memory. Now, UC San Francisco (UCSF) researchers have shown how this type of memory is consolidated during sleep, when the brain processes the learning of the day to make the physical act of doing something subconscious.

The study, published on December 14, 2022, in Nature, shows that the brain does this by reviewing the trial and error of a given action. In the analogy, that means sorting through every free throw Curry has ever taken, erasing memory for all actions except those that hit the mark, or that the brain decided were “good enough.” The result is the ability to take the free kick with a high degree of accuracy without having to think about the physical movements involved.

Even elite athletes make mistakes, and that’s what makes the game interesting. Engine memory is not about perfect performance. It’s about predictable mistakes and predictable successes. As long as the errors are stable from one day to the next, the brain says, ‘We’re going to block this memory.

Karunesh Ganguly, MD, PhD, professor of neurology and member of the UCSF Weill Institute for Neurosciences

Ganguly and his team discovered that the “locking” process involves surprisingly complex communication between different parts of the brain and takes place during deep restorative sleep known as non-REM sleep.

Sleep is important because our conscious brains tend to focus on failure, said Ganguly, who previously identified brain waves associated with sleep that influence skill retention.

“During sleep, the brain is able to filter all the prompts it has received and present the patterns that were successful,” he said.

Earth motor skills wouldn’t work on Avatar’s planet Pandora

It was once thought that learning motor skills only required the motor cortex. But in recent years a more complex picture has emerged.

To observe this process more closely, Ganguly put the rats on a task to reach the pellets. The team then 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 “rapid learning,” the PFC coordinated with the hippocampus, likely allowing the animal to perceive its movement relative 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 judgments, likely driven by reward centers that kicked in when the task was successful. It engaged in crosstalk with the motor cortex and hippocampus, turning down signals related to failures and increasing those related to successes.

Eventually, as the electrical activity of the regions became synchronized, the role of the hippocampus diminished, and the instances that the brain had signaled as rewarding came to the fore, where they were stored in what we call “motor memory.”

While the rats were initially learning the task, their brain signals were noisy and disorganized. As time passed, Ganguly was able to watch the signals sync up, until the rats did it about 70 percent of the time. After that point, the brain seemed to ignore the errors and maintained motor memory while the level of success remained stable. In other words, the brain begins to expect a certain level of error and does not update motor memory.

Like the NBA players, the rats mastered a skill based on a mental model of how the world works, which they created from their physical experience with gravity, space and other cues. But this type of motor learning would not easily transfer to a situation where the signals and the physical environment were different.

“If all of that were to change, for example, if Steph Curry was in the world of Avatar, she might not seem as skilled at first,” Ganguly said.

The best way to break a habit.

What if Curry hurt his finger and had to learn to shoot baskets a little differently? The study offered an answer.

“It’s possible to unlearn a task, but to do that, you have to stress the situation to the point where you’re making mistakes,” Ganguly said.

When the researchers made a slight change to the rats’ pellet-getting task, the rats made more errors and the researchers observed more noise in the rats’ brain activity.

The change was small enough that the rats did not have to go back to the beginning of their learning, only to the “breaking point” and relearn the task from there.

But because motor memory is embedded as a set of movements that occur over time, Ganguly said, changing motor memory in a complex movement like throwing a basketball may require changing a movement that is used to initiate the entire movement. sequence.

If Curry usually bounces a basketball twice before shooting it, Ganguly said, “It would be better to retrain the brain by just bouncing it once or three times. That way, you’d start from scratch.”

Fountain:

University of California – San Francisco

Magazine reference:

Kim, J. et al. (2022) Cortico-hippocampal coupling during multiplex scanning in the motor cortex. Nature. doi.org/10.1038/s41586-022-05533-z.

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