Sleep not only serves to consolidate memory and to fulfill a rest function, it would seem that it also plays a biological role of flushing out waste that has built up in the brain while we’re awake.

To protect themselves from any toxic molecules, nerve cells are not directly irrigated by the blood. The blood is filtered so that toxins do not come into contact with the neurons. One of these barriers is the cerebrospinal fluid (CSF) which flows through specific channels around and inside the brain. This fluid protects the brain from shocks and infections and carries nutrients to the brain.

Researchers assumed until now that the waste produced by the brain was recycled and not eliminated. A study published recently in the Science journal, however, shows that certain neuron support cells (glial cells) appear to have a different function during the day from that they play at night. While we are awake, they take part in neuronal activity. While we sleep, they eliminate waste expelled by the nerve cells that accumulates during the day in the interstitial space. This waste is picked up by the CSF and then taken to the liver.

This discovery is crucial, because not only does it shed light on understanding brain mechanisms, it opens up new ways of treating neuro-degenerative diseases, which are often caused by the accumulation of waste in the brain.