New research suggests that a good night’s sleep does more than just recharge your body—it literally clears your mind. Research published in the journal Cell reveals that deep sleep activates a natural brain-cleaning system, flushing out waste accumulated in the brains of mice during waking hours.
This discovery not only highlights the critical role of sleep in brain health but also raises questions about the long-term effects of sleep aids on this process.
Our brains come equipped with a built-in waste disposal system called the glymphatic system. This system circulates fluid through the brain and spinal cord to wash away toxins, including sticky proteins that can form plaques linked to neurological disorders like Alzheimer’s disease. Despite this understanding, scientists have long puzzled over what drives the glymphatic system—until now.
Researchers in Denmark have found that norepinephrine, a molecule typically associated with alertness, plays a surprising role during deep sleep. In their study on mice, they observed that the brainstem releases small waves of norepinephrine about every 50 seconds. These waves trigger blood vessels in the brain to contract and relax rhythmically, creating pulsations that help propel fluid and flush out waste.
“It’s like turning on the dishwasher before you go to bed and waking up with a clean brain,” Maiken Nedergaard, the study’s senior author and a researcher at the University of Rochester and the University of Copenhagen said in a recent statement. “We’re essentially asking what drives this process and trying to define restorative sleep based on glymphatic clearance.”
Significance of Getting a Good Night’s Sleep
The study revealed a complex interplay between norepinephrine waves, blood flow, and brain fluid movement. The researchers found that as norepinephrine levels rose and fell, the volume of blood in the brain fluctuated, creating rhythmic waves that correlated with cerebrospinal fluid flow. These synchronized movements help flush waste from the brain.
“You can view norepinephrine as this conductor of an orchestra,” lead author Natalie Hauglund of the University of Copenhagen and the University of Oxford mentioned in a recent press release. “There’s a harmony in the constriction and dilation of the arteries, which then drives the cerebrospinal fluid through the brain to remove the waste products.”
Sleep Aids and Brain Health
The researchers also explored whether all sleep is equally beneficial for the brain. To test this, they gave mice zolpidem, a commonly used sleep aid. While the drug helped the mice fall asleep faster, it reduced the norepinephrine waves during deep sleep by 50%. Consequently, brain fluid flow decreased by over 30%, impairing the glymphatic system’s waste-clearing function.
“More and more people are using sleep medication, and it’s really important to know if that’s healthy sleep,” Hauglund emphasized. “If people aren’t getting the full benefits of sleep, they should be aware of that so they can make informed decisions.”
Experts have long expressed concerns about the impact of sleep aids on achieving truly restorative sleep. While medications like zolpidem can help individuals fall asleep more quickly, research suggests they may interfere with the natural processes that make sleep beneficial.
For example, sleep aids often alter the brain’s sleep architecture, reducing the depth and quality of deep sleep. This disruption can impair essential functions like memory consolidation and, as recent studies suggest, the brain’s ability to clear out waste through the glymphatic system. As sleep disorders and reliance on sleep medications rise, scientists are urging caution, emphasizing the importance of understanding how these drugs may affect long-term brain health.
Implications for Human Health
Although the study was conducted on mice, the findings likely apply to humans, who also have a glymphatic system. Similar patterns of norepinephrine waves, blood flow, and brain fluid movement have been observed in humans.
“Now we know norepinephrine is driving the cleaning of the brain, we may figure out how to get people a long and restorative sleep,” says Nedergaard.
Kenna Hughes-Castleberry is the Science Communicator at JILA (a world-leading physics research institute) and a science writer at The Debrief. Follow and connect with her on BlueSky or contact her via email at kenna@thedebrief.org