After a sleepless night, those foggy, drifting moments may be more than fatigue — researchers at MIT say your brain might be cleaning itself mid-day. Their study, published this week in Nature Neuroscience, reveals that brief lapses in attention among sleep-deprived people coincide with waves of cerebrospinal fluid (CSF) flushing out of the brain — a cleaning process that normally takes place only during deep 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, in a press release.
Why Sleep Is More Than Rest for Your Brain
Sleep is essential for maintaining alertness and cognitive function, yet scientists are still uncovering why. One clue lies in CSF, which clears metabolic waste while we rest.
In 2019, Lewis’s lab showed that CSF moves in rhythmic waves during sleep, synchronized with brain-wave patterns. That steady flow, researchers believe, is crucial for keeping neurons healthy and functional. The new study asked a natural next question: What happens to that process when we miss a night of sleep?
Read More: Lack of Sleep Could be Causing an Increase in Mental Health Disorders
Watching the Sleep-Deprived Brain in Action
To find out, the team recruited 26 volunteers, testing each person twice — once after a full night’s sleep and once after staying up all night. Inside an MRI scanner, participants completed visual and auditory attention tasks while wearing EEG caps that measured brain activity. The researchers also tracked heart rate, breathing, and pupil size.
As expected, sleep-deprived participants performed worse. Their reactions slowed, and sometimes they didn’t respond at all. During those lapses, researchers observed waves of CSF flowing out of the brain, then back in when focus returned — a striking echo of sleep-time cleaning cycles.
“The results suggest that at the moment attention fails, this fluid is being expelled outward away from the brain,” Lewis explained in the press release. “And when attention recovers, it’s drawn back in.”
Your Heart, Breath, and Eyes All Join the Brain’s Cleanup
The team found that these attention lapses weren’t confined to the brain — they reverberated throughout the body. As focus slipped, heart rate and breathing slowed, pupils constricted, and cerebrospinal fluid surged, suggesting a tightly coordinated system linking mind 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 said. “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.”
That coordination, she added, may stem from a single control network that ties together thought and physiology.
“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,” said Lewis.
The researchers suspect that the noradrenergic system, which helps regulate alertness and bodily states through the neurotransmitter norepinephrine, could be the control hub behind this coordination. If so, every mental drift after a sleepless night may reveal just how intertwined our focus and physiology really are.
Read More: Women May Need More Sleep Than Men, but Research Is Unsure Why
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