During deep sleep, the brain may actively forget unimportant information

Rapid eye movement (REM) is a crucial stage in the sleep cycle associated with dreaming. The mechanics and purpose of REM sleep have long fascinated researchers, but a new study has found that the brain may actively forget or store information during this phase. 

When we slip away to dreamland and enter REM, breathing becomes erratic, heart rates increase, and the brain is host to a flurry of activity. 

It’s been suggested that REM plays an important role in storing new memories and eliminating excess information which could be why so few dreams are remembered the next day. 

Francis Crick, one of the discoverers of the DNA double helix, suggested that the brain actively forgets information during REM, but exactly how this happens was unknown until now. 

A team of researchers from the Center for Neuroscience at SRI International in California, Nagoya University in Japan, and Hokkaido University in Japan focused on cells that produce melanin-concentrating hormones (MCH) which are known to influence sleep and appetite. 

The researchers found that hypothalamic MCH cells sent messages to the hippocampus, the memory center of the brain. 

“From previous studies done in other labs, we already knew that MCH cells were active during REM sleep. After discovering this new circuit, we thought these cells might help the brain store memories,” said Dr. Thomas Kilduff, an author of the study.

Once this link was discovered, the researchers switched MCH neurons in mice on and off with different genetic tools and conducted memory tests. 

For one test, the mice had to distinguish between familiar and new objects. When the MCH cells were switched on as the mice retained information, it had a negative effect on memory, but when the cells were turned off, memory improved. 

The mice also performed better on memory tests when the MCH neurons were disabled during REM. 

“These results suggest that MCH neurons help the brain actively forget new, possibly, unimportant information,” said Dr. Kilduff. “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.”

The research, published in the journal Science, could help with finding new pathways for studying and treating sleep and memory disorders. 

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By Kay Vandette, Earth.com Staff Writer 

Image Credit: Shutterstock/Syda Productions