2021.08.26

Brain Refreshing: Why the Dreaming Phase Matters

Researchers from the University of Tsukuba and Kyoto University find that capillary blood flow in the brain, which is important for delivering oxygen and nutrients and removing waste products, is increased in mice during the dream-active phase of sleep.

Tsukuba, Japan—Scientists have long wondered why almost all animals sleep, despite the disadvantages to survival of being unconscious. Now, researchers led by a team from the University of Tsukuba have found new evidence of brain refreshing that takes place during a specific phase of sleep: rapid eye movement (REM) sleep, which is when you tend to dream a lot.

The researchers also measured electrical activity in the brain to identify REM sleep, non-REM sleep, and wakefulness, and looked for differences in blood flow between these phases. “We were surprised by the results,” explains Professor Hayashi. “There was a massive flow of red blood cells through the brain capillaries during REM sleep, but no difference between non-REM sleep and the awake state, showing that REM sleep is a unique state”

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