A team led by a Japanese researcher has identified neurons that remove memories during light sleep, when the body rests but the brain is still active.

A research paper by the team, led by Nagoya University professor Akihiro Yamanaka, has been published in the U.S. journal Science.

Dreams during light sleep just before awakening, a sleep phase called rapid eye movement (REM), are quickly forgotten partly due to these neurons, the team said.

Deep, non-REM sleep, when the brain is resting, occurs at the beginning of the sleep cycle, followed by alternating occurrences of REM and non-REM sleep. Memories are organized and processed during the cycle.

The identified neurons exist in small amounts in the brain’s hypothalamus, which helps regulate sleep, appetite, libido and body temperature. The neurons had been known for their role in stimulating the appetite.

The team had mice remember new objects and unpleasant locations, and artificially activated and inhibited the neurons.

The experiment found that when the neurons become active during REM sleep, the activity of the brain’s hippocampus — central to memory — is curbed, and memories are eliminated.

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