The brain cleans itself of toxic metabolic by-products while one is asleep and this cleansing could be the basic purpose behind the state of rest, say experts.
The brain's unique method of waste removal, dubbed the glymphatic system, is highly active during sleep, cleaning toxins responsible for Alzheimer's disease and other neurological disorders, revealed the US journal Science.
Researchers from the University of Rochester, New York, also found that during sleep the brain's cells reduce in size, allowing waste to be removed more effectively, Xinhua reported.
"This study shows that the brain has different functions when asleep and awake," said Maiken Nedergaard from the University of Rochester Medical Center.
Recent findings have also shown that sleep can help store and consolidate memories.
The glymphatic system acts like a plumbing system that piggybacks on the brain's blood vessels and pumps cerebral spinal fluid (CSF) through its tissues, flushing waste back into the circulatory system, the researchers said.
The glymphatic system is a waste clearance pathway in the central nervous system (CNS) of mammals.
Researchers speculated that the glymphatic system may be more active during sleep and carried series of experiments on mice by tracking the movements of red and green dye throughout the brain. They found that large amounts of CSF flowed into the brain of the mice during sleep, but not when they were awake.
The glymphatic system was almost 10-fold more active in them during sleep, researchers said.
"These findings have significant implications for treating disease like Alzheimer's," said Nedergaard.
Amyloid, a protein implicated in Alzheimer's disease, is a waste product removed by the system during sleep.
"Understanding how and when brain activates the glymphatic system and clears waste is a critical first step in efforts to potentially modulate the system and make it work more efficiently," he said.