Scientists have discovered a crucial mechanism behind one of sleep's most vital functions — cleaning toxins from the brain. The process relies on a rhythmic cycle of vessel squeezing and relaxing, driven by pulses of norepinephrine during deep sleep.
Researchers at the University of Copenhagen used advanced imaging techniques to watch brain blood vessels and fluid movements in real-time while mice slept naturally. They found that during non-REM sleep, the brain releases bursts of norepinephrine (a stress hormone) about every 50 seconds. These bursts cause blood vessels to constrict and then dilate in a coordinated pattern that acts like a pump, helping to flush waste products from brain tissue.
"What we discovered is essentially the brain's cleaning cycle during sleep," says lead author Natalie Hauglund. "When norepinephrine is released, it triggers blood vessels to squeeze, which then drives cerebrospinal fluid through the brain tissue to wash away metabolic waste products."
The findings, published in Cell, also revealed a downside to certain sleep medications. When researchers tested zolpidem (Ambien), they found it disrupted this cleaning mechanism by suppressing the natural norepinephrine pulses, potentially reducing the brain's ability to clear toxins during sleep.
"This explains why deep, natural sleep is so restorative," says senior author Maiken Nedergaard. "The rhythmic vessel movements we observed work like a wash cycle for the brain, but they only happen during natural sleep. Common sleep aids may help you fall asleep but could interfere with this essential cleaning process."
Previously:
• Texas Teachers suspended after knocking out kids with medicated 'sleeping stickers' (video)
• A man sacrificed sleep for 25 years to create history's most obsessive diary
