Sleep may literally clean the brain. New research suggests sleep may actually purge the brain of harmful molecules that cause neurodegeneration.
Researchers studied sleeping mice and found the space between their brain cells got wider during slumber. This could allow the brain to flush out toxins that have gotten caught between the cells during the waking hours, a National Institute of Neurological Disorders and Stroke (NINDS) news release reported.
"Sleep changes the cellular structure of the brain. It appears to be a completely different state," said Maiken Nedergaard, M.D., D.M.Sc., co-director of the Center for Translational Neuromedicine at the University of Rochester Medical Center in New York, and a leader of the study.
Sleep has always been a great mystery of mankind; researchers have only recently started to unlock the secrets behind why we need sleep to live. Scientists discovered that sleep played a key role in storing memories only within the past few years.
The team found that something called the glymphatic system works as a self-cleaning device in the brain during sleep. It allows fluid to rapidly flow through the brain. The glymphatic system was recently found the help control the flow of cerebrospinal fluid (CSF) which surrounds the brain and spine.
"It's as if Dr. Nedergaard and her colleagues have uncovered a network of hidden caves and these exciting results highlight the potential importance of the network in normal brain function," Roderick Corriveau, Ph.D., a program director at NINDS, said.
The team was able to watch the system in action by injecting dye into the CSF of the mice. The dye was observed to flow rapidly through the brain when the mice were asleep or under anesthesia, but barely flowed at all when they were awake.
"We were surprised by how little flow there was into the brain when the mice were awake," Nedergaard said. "It suggested that the space between brain cells changed greatly between conscious and unconscious states."
The team also used electrodes to directly measure the space between the rodents' brain cells.
"These are some dramatic changes in extracellular space," Charles Nicholson, Ph.D., a professor at New York University's Langone Medical Center and an expert in measuring the dynamics of brain fluid flow and how it influences nerve cell communication, said.
Brain cells called glia "control flow through the glymphatic system by shrinking or swelling." Noradrenaline is an "arousing hormone" that is believed to control cell volume.
"Treating awake mice with drugs that block noradrenaline induced unconsciousness and increased brain fluid flow and the space between cells, further supporting the link between the glymphatic system and consciousness," the news release reported.
The team also found that Beta-amyloid, a protein that has been linked to Alzheimer's, disappeared more quickly when the mice were asleep. The researchers concluded that sleep effectively cleared harmful substances from the brain.
"These results may have broad implications for multiple neurological disorders," Jim Koenig, Ph.D., a program director at NINDS said. "This means the cells regulating the glymphatic system may be new targets for treating a range of disorders."
"We need sleep. It cleans up the brain," Nedergaard said.
