Study Shows Sleep Flushes Toxins & Benefits Brain in Many Ways

A good night’s sleep is essential, but a new study shows getting your “Zs” is beneficial to the brain in countless ways, creating a new role “for sleep in health and disease.”

The study, funded and detailed in a press release by the National Institute of Neurological Disorders and Stroke (NINDS), shows how sleep helps us store memories.

"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.

Researchers used mice to show “for the first time that the space between brain cells may increase during sleep, allowing the brain to flush out toxins that build up during waking hours,” the NINDS press release says.

Highlights of the Study

• Dr. Nedergaard’s study showed sleep helps the brain rid itself of toxic molecules. Their results, published in Science, showed that during sleep “a plumbing system called the glymphatic system may open, letting fluid flow rapidly through the brain. Dr. Nedergaard's lab recently discovered the glymphatic system helps control the flow of cerebrospinal fluid (CSF), a clear liquid surrounding the brain and spinal cord.”
  
  
• Researchers injected dye into the cerebrospinal fluid of mice, “watching it flow through their brains while simultaneously monitoring electrical brain activity. The dye flowed rapidly when the mice were unconscious, either asleep or anesthetized. In contrast, the dye barely flowed when the same mice were awake.”
  
  
• "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."

The NINDS press release says researchers inserted “electrodes into the brain to directly measure the space between brain cells. They found that the space inside the brains increased by 60 percent when the mice were asleep or anesthetized.”

“These are some dramatic changes in extracellular space,” said 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.

Other Points from Study

• Certain brain cells, called glia, control flow through the glymphatic system by shrinking or swelling. Noradrenaline is an arousing hormone that is also known to control cell volume. Treating awake mice with drugs that block noradrenaline induced sleep and increased brain fluid flow and the space between cells, further supporting the link between the glymphatic system and sleep.
  
  
• Previous studies suggest that toxic molecules involved in neurodegenerative disorders accumulate in the space between brain cells. In this study, the researchers tested whether the glymphatic system controls this by injecting mice with radiolabeled beta-amyloid, a protein associated with Alzheimer’s disease, and measuring how long it lasted in their brains when they were asleep or awake. Beta-amyloid disappeared faster in mice brains when the mice were asleep, suggesting sleep normally clears toxic molecules from the brain. 

The bottom line is sleep is even more important than we think.

“We need sleep. It cleans up the brain,” said Dr. Nedergaard. 

(Top photo) SLEEP NATURALLY FLUSHES BRAIN: National Institute of Neurological Disorders & Stroke study shows sleep cleanses toxins from brain. Scientists watched dye move through the brain of a mouse. Photo: Courtesy of Nedergaard Lab, University of Rochester Medical Center.

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