Why Do We Dream?

The function of dreams has been a long-debated topic in the scientific community. After all, there must be some benefit to deep, restful sleep if we evolved to do so while still being hunted by giant, terrifying, pre-historic beasts. However, the question still remains—why exactly do we dream?

The study

Recently, researchers at the University of Tsukuba have attempted to answer this very question. In their 2021 study, they monitored blood flow in the brain capillaries of mice – a crucial part of oxygen and nutrient delivery as well as waste removal – during REM sleep. To do this, they used a technique called “two-photon microscopy” whereby blood vessels in the brain were marked with a special dye which is visible under fluorescent light. Cool, huh?

They distinguished the different sleep phases by measuring electrical activity in the brain, allowing them to compare periods of high blood flow with corresponding levels of brain activity. What they found surprised the researchers.

“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 is a unique state,” Professor Hayashi, an author of the paper, commented.

Interestingly, an association was also found to exist between increases in blood flow and sleep strength. To test this, the researchers disrupted the mice’s sleep causing them to enter into “rebound” REM sleep – a more intense form of REM sleep – and once again monitored changes in brain blood flow. The results showed that rebound REM was associated with an even greater increase in blood flow in the brain capillaries.

What does this mean?

This suggests that REM sleep plays a very important role in removing waste products from the brain—a function which could have profound implications for the future treatment of diseases such as Alzheimer’s which are associated with a build-up of waste products in the brain.

So, it seems like there’s a reason we feel lighter after a good night’s rest! Maybe it’s time to invest in a comfier mattress?

To learn more, read the Science Daily article below: