Scientists discover that sleep may not clear toxins in the brain

The brain’s ability to get rid of toxins may actually be reduced during sleep, contrary to leading scientific theory.

For the past decade, the main explanation for why we sleep has been that it allows the brain to flush out toxins. However, a new study led by scientists at the UK Dementia Research Institute (UK DRI) at Imperial College London indicates that this may not be true.

By measuring toxin clearance and fluid movement in the brains of mice, they showed that it was significantly reduced during sleep and under anesthesia.

The researchers used a fluorescent dye and watched how quickly the dye moved from one part of the brain to another and was removed from the brain. This allowed them to directly measure the rate at which the dye was removed from the brain. They found that clearance of the dye was reduced by about 30% in sleeping mice, and by 50% in anesthetized mice, compared to mice kept awake.

Previously, the leading theory was that sleep improves the elimination of toxins from the brain, which happens via the glymphatic system (a mechanism that flushes waste from the central nervous system). However, this has never been conclusively confirmed and previous studies relied on indirect ways of measuring fluid flow through the brain.

According to the researchers, the latest findings are surprising and more work is now needed to understand exactly what is happening, and why. Their job is published in the magazine Nature Neuroscience.

Professor Nick Franks, Professor of Biophysics and Anesthesia at Imperial College London, and co-leader of the study, said: “The field has been so focused on the idea of ​​clearance as one of the main reasons we sleep that we were very surprised to find it opposite observed in our results. We found that the rate at which dye was removed from the brain was significantly reduced in animals that were sleeping or anesthetized.

“So far we don’t know what it is about these states that slow the removal of molecules from the brain. The next step in our research will be to try to understand why this happens.”

The size of molecules can affect how quickly they move through the brain, and some compounds are removed through different systems. Therefore, the extent to which the findings are generalizable has not yet been confirmed.

Professor Bill Wisden, interim director of the UK Dementia Research Institute at Imperial, and co-leader of the study, explained: “Although we have shown that clearing out toxins may not be the main reason why we sleep, it cannot be disputes that sleep is important.

“Disturbed sleep is a common symptom that people with dementia experience, but we still don’t know whether this is a consequence or a driving factor in the progression of the disease. It may well be that a good night’s sleep for reasons reduces the risk of helps reduce dementia.” other than cleaning up toxins.

“The other side of our study is that we showed that brain clearance is very efficient during the waking state. In general, being awake, active and exercising can cleanse the brain of toxins more efficiently.”

The researchers next want to discover how sleep reduces the clearance of toxins from the brain in mice, and investigate whether their findings are applicable to humans.