How “brainwashing” while sleeping clears waste away

It turns out a little brainwashing on a regular basis might be good for you. That’s because during your waking hours, your brain is accumulating waste from all the work it’s doing, and it needs to be washed away through sleep. Now scientists have figured out the mechanism by which the brain transports waste-filled fluid out of the brain during sleep (Cell 2025, DOI: 10.1016/j.cell.2024.11.027).

The system that clears waste from the brain is called the glymphatic system, a term first coined in 2012 by Maiken Nedergaard, a glial cell biologist at the University of Rochester Medical Center and corresponding author on the research paper describing the work. She says that this system is “basically like a dishwasher” that runs while you sleep, cleaning up waste products that can cause disease, including amyloid and τ proteins, that accumulate during periods of wakefulness.

Since 2012, researchers have uncovered bits and pieces about how the glymphatic system works. But until now, the mechanism that drove fluid transport in the brain wasn’t well understood.

The new research, performed using a mouse model, shows that during sleep, the brain releases waves of the neurotransmitter norepinephrine every 50 s. The norepinephrine stimulates blood vessels in the brain to contract, creating what Nedergaard calls a “rhythmic oscillation” that drives the movement of blood and cerebrospinal fluid in the brain and ultimately causes the waste to be filtered out.

Laura Lewis, a neuroscientist at the Massachusetts Institute of Technology who isn’t affiliated with the study, praises the new research, saying that it shows that “oscillating infraslow waves [of blood vessel constriction] in sleep structure is a key force in brain fluid dynamics.” Future work will need to translate these results from mice into humans, but Lewis says there are enough parallels between mice and human brains that it’s likely several aspects of the work will translate.

Nedergaard says all of this goes to show that sleep is an extremely complex process, and one necessary to keep our brains in good working condition. The glymphatic system can’t function when one is awake because it would cause too much noise in the brain, interfering with waking processes. Furthermore, the research showed that the use of sleep-aiding drugs reduced the amount of waste the brain could clear during sleep.

“Sleep is so much more than just disconnecting from the surroundings. It’s really a very active period of housekeeping,” Nedergaard says.