A good night’s sleep can literally clear your mind.

New research shows how deep sleep helps remove waste that builds up in the brain while you’re awake, playing a key role in maintaining brain health.

Scientists from Denmark have found that a molecule called norepinephrine plays an important role in clearing the brain in mice. During deep sleep, the brain stem releases small waves of norepinephrine approximately every 50 seconds. This process causes the blood vessels to contract, creating slow pulsations that provide a rhythmic flow in the surrounding fluid to remove waste.

The researchers correlated changes in blood volume with the movement of brain fluid and found that fluid flow fluctuated with blood volume, suggesting that the vessels act as pumps, moving brain fluid to remove waste.

The team then asked a new question: Is everyone’s sleep process the same? To answer this, the researchers gave mice zolpidem, a popular sleep drug. It turned out that in mice treated with zolpidem, norepinephrine waves during deep sleep were 50% weaker than in those who slept without the drug. Even though the zolpidem-treated mice fell asleep faster, fluid movement in the brain was reduced by more than 30%. These results suggest that sleeping pills may interfere with the brain’s norepinephrine-related waste clearance process during sleep.

The scientists suggest that the study’s findings may apply to humans since they also have a glymphatic system, although this requires more observation. In humans, similar norepinephrine waves, blood circulation patterns, and brain fluid flow have been identified. These findings may help understand how insufficient sleep may contribute to the development of neurological diseases such as Alzheimer’s disease.