While we’re asleep, our brains are doing more than recharging for the next day. They’re also tidying up, using a cleaning process scientists hope could lead to treatments for ‘dirty brain’ diseases like Alzheimer’s.
Sleep can flush toxins from the brain that accumulate during the course of the day according to a study which may change understanding about the biological purpose of sleep.
“This study shows that the brain has different functional states when asleep and when awake,” said Maiken Nedergaard, M.D., D.M.Sc., co-director of the University of Rochester Medical Center (URMC) Center for Translational Neuromedicine and lead author of the article. “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.”
Researchers said the study revealed that the brain’s unique method of waste removal – dubbed the glymphatic system – is highly active during sleep, clearing away toxins responsible for Alzheimer’s disease and other neurological disorders. Furthermore, the researchers found that during sleep the brain’s cells reduce in size, allowing waste to be removed more effectively.
Since the lymphatic system, which is responsible for disposing cellular waste from the rest of the body, does not extend to the brain, scientists had long puzzled about how the brain cleaned itself.
Using two-photon miscroscopy to study mice brains, the researchers discovered what they call a “plumbing system that “piggybacks” on the brain’s blood vessels and pumps cerebral spinal fluid (CSF) through the brain’s tissue, flushing waste back into the circulatory system and onto the liver for filtering.
The accumulation of waste in the brain can lead to diseases such as Alzheimer’s disease.
The researchers said that since pumping CSF demands a great deal of energy, it might perhaps be better to do it when the brain is not occupied with processing information during waking hours
“The brain only has limited energy at its disposal and it appears that it must choice between two different functional states – awake and aware or asleep and cleaning up,” said 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.”
Researchers also found that cells in the brain “shrink” by 60 percent during sleep. They said the contraction allows more space between the cells, which allows the CSF to flow through more freely.
“These findings have significant implications for treating ‘dirty brain’ disease like Alzheimer’s,” said Nedergaard. “Understanding precisely how and when the brain activates the glymphatic system and clears waste is a critical first step in efforts to potentially modulate this system and make it work more efficiently.”
The study was published in the journal Science.