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How Sleep Flushes Toxins From Your Brain

Sleep is a vital part of a healthy lifestyle. Without it, you put yourself at risk for numerous physical and mental health conditions. There’s no doubt that skimping on sleep will cost you — but hopefully, you already know that. What you may not know, is that restful and restorative sleep can actually flush toxic waste out of your brain.

Scientists discovered the link between sleep and cognition and brain health long ago. But a new study is now providing deeper insight into the connection. The study, led by neuroscientist Laura Lewis of Boston University, set out to discover the way that cerebrospinal fluid (CSF) flushes toxic waste from the brain during sleep. Lewis explained, “We know sleep is really important for brain health, and waste clearance is probably a key reason why; what was less clear is: Why is this changed during sleep? That led us to ask what was happening in the CSF.”

The researchers monitored the brain waves of 13 healthy adults while they slept, using electroencephalography (EEG), along with an advanced fMRI technique that was able to capture changes at a faster rate than a standard fMRI. They found that in non-REM sleep, the slow waves occurred simultaneously with changes in blood flow and CSF, suggesting that as brain activity causes changes in blood flow, the volume of blood in the brain is reduced, and CSF then flows in to fill up the space.

Lewis explained, “We’ve discovered there are really large waves of CSF that appear in the brain only during sleep. This effect is really striking, and we’re also interested in what it means for maintaining brain health, especially in disorders such as Alzheimer’s disease.”

Researchers hope to further study CSF flow as it relates to neurodegenerative diseases caused by toxic protein buildup in the brain. “We know that people with Alzheimer’s have fewer slow waves, so we may find they also have fewer CSF waves,” Lewis said.

The study may hold answers to other disorders in which sleep disturbance is a common feature, such as depression and schizophrenia. Lewis added, “Different electrical signatures of sleep are disrupted in different psychiatric conditions. So this will be very interesting to follow up on in a multitude of disorders.”