For many years, scientists have been fascinated by the significant role sleep plays in our everyday lives. Evidence shows that a good night’s sleep has the following effects on the individual: Improved learning, increased reaction timing, and better cognitive testing.
A mouse study proposes a new function for sleep. Dr. Maiken Nedergaard and her colleagues at the University of Rochester Medical Center suggests that sleep is used to restore the brain from toxin buildup during waking hours, via the brain’s custodian system called the glymphatic system. Their results show the glymphatic system helping control the flow of cerebrospinal fluid and sweeping through the brain.
The researchers injected a dye into the cerebrospinal fluids of mice, monitored the dye flow, and measured the brain’s electrical activity. Their results show the dye disappearing from the brain twice as quickly when the mice were either asleep or anesthetized as opposed to when the mice were awake and alert.
“We were surprised by how little flow there was into the brain when the mice were awake,” said Dr. Nedergaard. “It suggested that the space between brain cells changed greatly between conscious and unconscious states.”
To test the spacing of brain cells between conscious states, the research team inserted electrodes directly into the mice’s brains. Natural sleep and anesthesia were associated with a 60 percent increase of the spacing between brain cells. Also, an increased clearance rate of beta-amyloid, a protein associated with Alzheimer’s disease, was observed during sleep.
“These are some dramatic changes in extracellular space,” said Charles Nicholson, Ph.D., a professor at New York University’s Langone Medical Center.
Previous studies, like Alzheimer’s disease, suggest accumulation of toxic molecules in the space between brain cells may be the source of multiple neurodegenerative disorders. “These results may have broad implications for multiple neurological disorders,” said Jim Koenig, Ph.D., a program director at NINDS. “This means the cells regulating the glymphatic system may be new targets for treating a range of disorders.”
This study demonstrates how essential sleep is for the restoration of the brain.