How Sleep Clears Our ‘Dirty’ Brains

Sleep has many restorative benefits including improving memory retention, reasoning, problem-solving, and attention to detail. However, a recent study indicates another more important reason to get a good night’s sleep—it clears a “dirty brain” by flushing out toxins that accumulate during waking hours.

Dr. Maiken Nedergaard and her research team at the University of Rochester Medical Center recently studied the glymphatic system, a system that moves clear cerebrospinal fluid throughout channels surrounded by blood vessels. The glymphatic system is vitally important to brain health as it removes the toxic protein beta-amyloid from brain tissue. If beta-amyloid are allowed to accumulate within the brain it can cause neurological diseases such as Alzheimer’s.

The scientists wanted to determine if sleep could aid beta-amyloid clearance from the brain by regulating its glymphatic system. The team first injected dye into mice’s cerebrospinal fluid and then monitored the animals’ electrical brain activity by tracing the dye flow. The step confirmed prior studies findings that the dye barely flowed when the mice were awake, but flowed rapidly when they were asleep or anesthetized.

The researchers then injected mice with labeled beta-amyloid and measured how long the proteins lasted in their brains while they were awake and asleep. They discovered that the beta-amyloids disappeared twice as quickly from the brains of mice when they were asleep. Lastly, the researchers tested whether the hormone noradrenaline, which causes alertness, might affect the glymphatic system. When the mice were injected with a drug that blocks noradrenaline, it caused a sleep-like state that increased brain fluid flow, indicating there was a molecular connection between the brain’s cleaning system and the sleep-wake cycle.

The study’s findings suggest that neurological disorders may be treated, or even be prevented, by manipulating the body’s glymphatic system.

 “These findings have significant implications for treating ‘dirty brain’ diseases like Alzheimer’s,” Nedergaard said to National Institute of Health. “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.”

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