Sleep deprivation may trigger brain’s “cleaning” process, study finds

After a sleepless night, you might feel foggy or find it harder to concentrate, but new research suggests that these lapses in attention could be more than just fatigue.

A study published this week in Nature Neuroscience by researchers at MIT reveals that during periods of sleep deprivation, the brain may begin a cleaning process typically reserved for deep sleep, Discover magazine writes.

The study found that, in people who had missed a night of sleep, brief moments of inattention were closely tied to waves of cerebrospinal fluid (CSF) flushing out of the brain—a process usually seen only during sleep.

“If you don’t sleep, the CSF waves start to intrude into wakefulness where normally you wouldn’t see them. However, they come with an attentional tradeoff, where attention fails during the moments that you have this wave of fluid flow,” said Laura Lewis, the senior author of the study.

The discovery adds to the growing body of evidence suggesting that sleep is vital not just for rest, but for maintaining cognitive function. CSF, the clear fluid that surrounds the brain and spinal cord, plays an important role in clearing metabolic waste during sleep.

Lewis’s lab had previously shown in 2019 that CSF moves in rhythmic waves during sleep, synchronized with brain wave patterns. This flow is believed to be essential for keeping neurons healthy and functional. The new study sought to explore what happens to this process when a person misses out on sleep.

In their experiment, the researchers recruited 26 volunteers and tested them twice: once after a full night’s sleep, and once after staying up all night. While in an MRI scanner, participants completed visual and auditory attention tasks, all while wearing EEG caps to measure brain activity. The study also monitored heart rate, breathing, and pupil size.

As expected, sleep-deprived participants performed worse. Their reactions slowed, and sometimes they didn’t respond at all. But what was more striking were the observations made during these lapses in attention. Researchers noted that during these moments, CSF waves would flow out of the brain, only to return when attention and focus were restored.

“The results suggest that at the moment attention fails, this fluid is being expelled outward away from the brain,” Lewis explained. “And when attention recovers, it’s drawn back in.”

This process, however, wasn’t limited to the brain alone. The study found that as attention faltered, there were physical changes in the body as well: heart rate slowed, breathing became more shallow, and pupils constricted. CSF surged, indicating a synchronized event linking brain and body.

“What’s interesting is it seems like this isn’t just a phenomenon in the brain, it’s also a body-wide event,” Lewis noted. “It suggests that there’s a tight coordination of these systems, where when your attention fails, you might feel it perceptually and psychologically, but it’s also reflecting an event that’s happening throughout the brain and body.”

The research points to the possibility of a single control network that connects mental focus with physiological processes.

“These results suggest to us that there’s a unified circuit that’s governing both what we think of as very high-level functions of the brain — our attention, our ability to perceive and respond to the world — and also really basic physiological processes like fluid dynamics, brain-wide blood flow, and blood vessel constriction,” Lewis explained.

The team speculates that the noradrenergic system, which regulates alertness and bodily states via the neurotransmitter norepinephrine, could be at the heart of this coordination. If this theory holds, it would suggest that every mental lapse following sleep deprivation is not just a cognitive slip, but a deeper reflection of how the brain and body work in tandem to maintain balance.

By Sabina Mammadli