Researchers find how the brain actively forgets memories during sleep

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Scientists identified neurons in mice that are involved in actively forgetting memories during dream sleep.

Rapid eye movement is a unique sleep stage first happens about 90 minutes after falling asleep. A single night’s sleep can have several sleep cycles that include REM sleep.

Researchers have long suspected that REM sleep is vital to storing memories as well as a time when the brain actively forgets excess information to prevent overload.

Recent studies in mice showed that the brain trims away connections between neurons involved in certain types of learning during sleep.

A research team funded in part by the National Institutes of Health to explore the brain circuits involved in memory storage while dreaming.

The researchers used a special staining process to identify neurons which produce melanin concentrating hormone which the team suspected might also play a role in memory and learning.

The scientists then used genetic tools to turn individual MCH neurons on and off in mice during memory tasks. When MCH neurons were turned on the mice’s memory worsened. Turning the MCH neurons off or eliminating them altogether improved memory.

“Since dreams are thought to primarily occur during REM sleep, the sleep stage when the MCH cells turn on, activation of these cells may prevent the content of a dream from being stored in the hippocampus—consequently, the dream is quickly forgotten,” said Dr. Thomas Kilduff of SRI International, who led the study.

The researchers also found that the effects were exclusive to REM sleep. Mice performed better on memory tasks when MCH neurons were turned off during REM sleep, but turning off the neurons while the mice were awake or in other sleep states had no effect on memory.

Understanding sleep’s role in memory storage may be used for researching memory-related diseases like post-traumatic stress disorder and Alzheimer’s disease.

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