Researchers show how motor memory is consolidated during sleep

In a study done by Jaekyung Kim and colleagues (2022), it has been shown that motor memory is consolidated during sleep. The consolidation of this type of memory occurs by reviewing the trials and errors of a given action. This results in the ability to perform the action with a high level of accuracy without consciously thinking about the physical movements involved. The process of "locking in" this learning involves complex communication between different parts of the brain and occurs during non-REM sleep, a deep and restorative stage of sleep. This is important because our conscious brains tend to focus on failures, and sleep allows the brain to identify and reinforce successful patterns of learning and performance.

It was previously believed that learning motor skills only involved the motor cortex, but the current research has revealed that it is more complex than that. In order to better understand this process, the scientists used rats to perform a task that involved reaching for pellets, and then examined their brain activity in three regions during NREM sleep: the hippocampus (which is responsible for memory and navigation), the motor cortex, and the prefrontal cortex (PFC). Over the course of 13 days, the researchers observed a pattern of "fast learning," in which the PFC coordinated with the hippocampus to enable the animals to perceive their motion and location in space. During this phase, the brain appeared to be exploring and comparing various actions and patterns learned while practicing the task.

In a process known as slow learning, the PFC appears to make value judgments based on reward centers that are activated when the task is successful. It engages in communication with the motor cortex and the hippocampus, enhancing signals related to successful outcomes and suppressing signals related to failures. As the electrical activity of these regions becomes synchronized, the role of the hippocampus decreases and successful actions become dominant in the memory, a process known as "motor memory." During the initial stages of learning, the brain signals of the rats were disorganized and noisy, but over time the signals became synchronized and the rats were successful in the task about 70% of the time. At this point, the brain seemed to ignore mistakes and maintain the motor memory as long as the level of success remained stable. However, this kind of motor learning may not easily transfer to a situation with different physical cues or environment.

The study suggests that it is possible to unlearn a task by introducing stress or changes that cause mistakes. When the researchers made a slight modification to the rats' task of obtaining pellets, the rats made more errors and the researchers observed more noise in their brain activity. The change was small enough that the rats did not have to go back to the beginning of their learning, but rather relearn the task from the "breaking point" where the errors occurred. Because motor memory becomes ingrained as a series of movements that follow each other in time, it may be necessary to change the initiating movement in a complex action in order to retrain the brain and start with a "clean slate."

References:

Henderson, E. (2022, December 20). Researchers show how motor memory is consolidated during sleep. News Medical. Retrieved December 20, 2022, from https://www.news-medical.net/news/20221219/Researchers-show-how-motor-memory-is-consolidated-during-sleep.aspx

Kim, J., et al. (2022) Cortical–hippocampal coupling during manifold exploration in motor cortex. Nature.doi.org/10.1038/s41586-022-05533-z.