University of Rochester Medical Center research reports that while we sleep, our brains flush out toxins that are build up when we’re awake. During sleep, the brain cleans itself.

The brain has a unique method of waste removal, known as the glymphatic system, a kind of plumbing system that washes away toxins by pumping cerebral spinal fluid (CSF) through spaces between brain cells. Interestingly, Xie and colleagues found that the glymphatic system was almost 10 times more active during sleep.

Having enough sleep is very important to our health. A deficit can compromise our immune systems, cause inflammation, lead to memory loss and weight gain, hamper reflexes and decision-making skills, and increase the risk of chronic diseases like cancer and type 2 diabetes.

While we slumber, report researchers at the University of Rochester Medical Center in the journal Science, our brains flush out toxins that build up when we’re awake — allowing us to clear our heads.

Scientists watched dye flow through the brain of a sleeping mouse


By tagging beta-amyloid with fluorescent tags, the scientists saw that this waste protein flowed out of the brain twice as fast during sleep. In fact, the flow of waste out of the brain during the waking state was only 5 per cent of that when the mice were asleep.

“This study shows that the brain has different functional states when asleep and when awake,” says Dr Maiken Nedergaard, who supervised the study. “In fact, the restorative nature of sleep appears to be the result of the active clearance of the by-products of neural activity that accumulate during wakefulness.”

Importantly, the brain can only clean itself during sleep. “The brain only has limited energy at its disposal and it appears that it must choose between two different functional states: awake and aware, or asleep and cleaning up,” says Nedergaard.

“You can think of it like having a house party. You can either entertain the guests or clean up the house, but you can’t really do both at the same time.”

The glymphatic system in our brains serves as plumbing: It includes a network of passageways between the brain’s cells that controls the flow of the clear liquid surrounding the brain and spinal cord, known as cerebrospinal fluid.

These passageways undergo dramatic changes between sleep and waking moments. Specifically, the study showed, sleep increases the space where cerebrospinal fluid circulates by 60 percent, allowing room for unnecessary byproducts to be flushed from the brain.

For example, almost every neurodegenerative disease — including Alzheimer’s — is associated with the buildup of toxic proteins in the brain. Researchers suspect that it is the accumulation of these proteins that can kill neurons and lead to dementia. Sleep appears to support the brain’s innate ability to identify and dump these damaging proteins.


“Sleep changes the cellular structure of the brain,” Nedergaard says. “It appears to be in a completely different state.”