This Is Why Dreaming Is So Important.
Scientists have long questioned why nearly all creatures sleep, despite the obvious costs of being unconscious for survival. Now, researchers led by a team from the University of Tsukuba have discovered new evidence for brain rejuvenation occurring during a specific period of sleep: rapid eye movement (REM) sleep, which is associated with vivid dreams.
Previous research has used a variety of methodologies to determine the variations in blood flow in the brain between REM sleep, non-REM sleep, and alertness, with inconsistent results. The Tsukuba-led research has developed a technology for directly visualizing the movement of red blood cells in mice’s brain capillaries (areas where nutrients and waste products are transferred between brain cells and blood).
“We employed a chemical to make the brain blood veins visible under fluorescent light, a technique called two-photon microscopy,” explains Professor Yu Hayashi, senior author of the study. “In this method, we were able to detect red blood cells directly in neocortical capillaries in awake mice.”
Additionally, the researchers searched for variations in blood flow between REM sleep, non-REM sleep, and awake by measuring electrical activity in the brain.
“We were taken aback by the results,” Professor Hayashi admits. “During REM sleep, there was a tremendous influx of red blood cells through the brain capillaries, but no change between non-REM sleep and the waking state, indicating that REM sleep is a distinct condition.”
The researchers next interrupted the mice’s sleep, causing them to experience “rebound” REM sleep – a stronger version of REM sleep that compensates for the earlier interruption. The brain’s blood flow was further boosted during rebound REM sleep, implying a relationship between blood flow and the strength of REM sleep. However, when the same trials were done with mice lacking adenosine A2a receptors (the receptors that make you feel more awake after drinking coffee), there was less of an increase in blood flow during REM sleep, even during rebound REM sleep.
“These findings show that adenosine A2a receptors may be involved in at least some of the alterations in brain blood flow that occur during REM sleep,” Professor Hayashi explains.
Given that decreased blood flow to the brain and decreased REM sleep are associated with the development of Alzheimer’s disease, which is characterized by the accumulation of waste products in the brain, it may be worthwhile to investigate whether increased blood flow through the brain capillaries during REM sleep is necessary for waste removal from the brain. This study lays the framework for further research into the involvement of adenosine A2a receptors in this process, which may eventually result in the development of new treatments for illnesses such as Alzheimer’s disease.