Most of our dreaming occurs during REM cycles of our sleep, but there is still some debate in the scientific community surrounding the purpose of dreaming and different sleep cycles. Hoping to shed some light on why we sleep and dream, researchers from the University of Tsukuba decided to look at how blood flow in the brain changes throughout sleep.

The researchers measured the differences in ​​red blood cells in the brain capillaries, the area of the brain where nutrients and waste products are exchanged between brain cells and blood, and found that there is a drastic increase in red blood cells through the brain during REM sleep.

Even more surprisingly, they found no difference in red blood cell concentration between non-REM sleep and awake states, indicating that REM is particularly unique. To monitor red blood cell concentrations, the team used dye to make the brain blood vessels visible under fluorescent light.

In addition to demonstrating the importance of REM, the researchers also found that when REM sleep is disrupted, the brain compensates for this disruption with an even deeper REM cycle and increased blood flow. They also found that mice without A2a receptors saw less of an increase in blood flow during REM sleep, indicating that these receptors play a role in regulating blood flow during sleep.

So what does this all mean? This discovery about the correlation between blood flow and REM sleep could provide insights into the development of Alzheimer’s disease. Reduced blood flow in the brain and decreased REM sleep are both signs of Alzheimer’s, and this research indicates that the lack of waste-removing blood flow during REM sleep could be a primary contributor to symptoms of Alzheimer’s. More research needs to be done to establish this correlation more concretely, but this initial study offers promising potential for new Alzheimer’s treatment and diagnosis methods.

Source study: Cell Reports – Cerebral capillary blood flow upsurge during REM sleep is mediated by A2a receptors