REM Sleep Refreshes the Brain: Researchers Found Evidence of Increased Cerebral Blood Flow During the Dream Phase

Sleep is essential to all animals and humans, as important as eating, drinking, and breathing. Doctors have warned of possible health consequences from lack of sleep, ranging from drowsy driving and irritability to an increased risk of developing dementia and premature death.

Scientists have been studying the importance of sleep to overall health, but researchers from the University of Tsukuba found for the first time evidence of increased cerebral blood flow during REM sleep when vivid dreams occur, which refreshes the brain as wastes are removed.

REM Sleep vs. Non-REM Sleep

The National Institutes of Health (NIH) said that quality sleep is as essential as food and water as it affects overall functioning. But simply sleeping does not automatically qualify it to be quality sleep. There are two types of sleep, which are non-REM sleep and REM sleep.

According to WebMD, rapid eye movement (REM) sleep is when the eyes move around rapidly in various directions but do not send visual messages to the brain. But before reaching that phase, non-REM sleep comes first.

It is when the eyes are closed, and the person is in light sleep, heart rate slows, and body temperatures drop. It is the phase of sleep when the body prepares for deep sleep, when the person is harder to rouse, or when they woke up, they feel disoriented for a few minutes.

As people get older, they tend to find it harder to get deep sleep, which is problematic since everyone still needs as much sleep as young people do.

After the non-REM sleep comes to the REM sleep that usually happens 90 minutes after falling asleep, the first part of this phase lasts for 10 minutes, while each succeeding stages get longer. In this stage, heart rate and breathing quicken as the person dreams, and the brain becomes more active.

Previous studies found that REM sleep is important because it stimulates brain parts that are responsible for learning. Researchers from the University of Tsukuba explained how this phase refreshes the brain.

REM Sleep Refreshes the Brain

In the study, titled "Cerebral Capillary Blood Flow Upsurge During Rem Sleep Is Mediated by a2a Receptors," published in Cell Reports, researchers used a dye to observe the flow of red blood cells in capillaries under fluorescent light using a technique called two-photon microscopy.

Study senior author Professor Yu Hayashi explained in the university's news release that this method would allow them to directly observe red blood cells in the capillaries located in the neocortex of the unanesthetized mice.

International Business Times reported that researchers measured electrical activity during non-REM sleep, REM sleep, and when the mice were awake. The team found increased cerebral blood flow in the capillaries during REM sleep but none during NREM sleep and awake state.

Capillaries are blood vessels that deliver nutrients and oxygen and remove waste products. This means that increased cerebral blood flow in this area suggests a link between REM sleep and brain refreshing methods.

Moreover, adenosine A2a receptors at the molecular level might also be responsible for the increased blood flow in the brain during REM sleep.

Researchers believe that the role of adenosine A2a receptors in this process could help future researchers develop new treatments for Alzheimer's disease, a brain disorder linked to reduced blood flow in the brain and decreased REM sleep that led to a buildup of waste products in the brain.

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