Summary: New research reveals that after a night of poor sleep, brief lapses in attention coincide with pulses of cerebrospinal fluid (CSF) leaving the brain—the same cleansing process that normally occurs during deep sleep. Using simultaneous EEG and fMRI, researchers show these fluid pulses align precisely with attention failures, suggesting the brain attempts to recover some missed restorative processes while awake.
This partial compensation, however, carries a substantial cost: reduced alertness and slower reaction times. The study links attention, brain cleansing, and whole-body physiology, offering insight into why fatigue so strongly impairs concentration and performance.
Key Facts
- Cleansing tradeoff: When sleep-deprived, the brain triggers CSF pulses normally observed during sleep, and those pulses coincide with brief attention failures.
- Coordinated response: These lapses are accompanied by slower breathing, reduced heart rate, and pupil constriction, indicating a body-wide coordinated event.
- Unified circuit: The results suggest a single neural system may coordinate attention, arousal, and physiological processes such as fluid flow and cardiovascular changes.
Source: MIT
Nearly everyone has experienced it: after a night of poor sleep you feel less alert, your thinking is sluggish, and your mind drifts when you need to concentrate.
A new study from MIT examines what happens in the brain during those momentary attention failures. The researchers found that when attention lapses after sleep loss, a wave of CSF flows out of the brain—the same flushing action that normally occurs during deep sleep to remove metabolic waste. This cleaning process is thought to be essential to preserve healthy brain function.
When sleep is restricted, the brain appears to try to make up for missed cleansing by initiating brief CSF pulses while awake. Although this may partially restore some restorative functions, it also interrupts attention and slows reactions.
“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,” says Laura Lewis, the Athinoula A. Martinos Associate Professor of Electrical Engineering and Computer Science at MIT, a member of the Institute for Medical Engineering and Science and the Research Laboratory of Electronics, and an associate member of the Picower Institute for Learning and Memory.
Lewis is the senior author of the study, published in Nature Neuroscience. MIT postdoctoral associate Zinong Yang is the lead author.
Flushing the brain
Although sleep’s full functions remain under investigation, it is clear that sleep is essential for maintaining alertness and cognitive performance. Prior work by Lewis and colleagues showed that during sleep CSF flows in a rhythmic pattern linked to brain wave activity, supporting the idea that sleep enables a daily brain-cleaning cycle.
To test how sleep deprivation affects those dynamics, the team enrolled 26 volunteers and tested each person twice: once after a night awake in the lab and once when well rested. The next morning, participants performed attention tasks inside an fMRI scanner while wearing an EEG cap. The fMRI method was adapted to track not only blood oxygenation but also CSF flow in and out of the brain. Researchers also recorded heart rate, breathing rate, and pupil diameter.
Participants completed two standard attention tasks—one visual and one auditory. In the visual task, they watched a screen with a fixed cross that randomly changed into a square; they were instructed to press a button whenever they saw that change. In the auditory version, a beep served as the cue. As expected, sleep-deprived participants performed worse: responses were slower and, for some stimuli, the change went undetected entirely.
Crucially, during those brief lapses of attention the team observed a set of synchronized physiological changes. Most prominently, a pulse of CSF flowed outward from the brain precisely when attention failed; when attention returned, CSF flowed back in. The team also saw transient reductions in breathing and heart rate, along with pupil constriction that began roughly 12 seconds before the CSF pulse and reversed after attention recovered.
“The results suggest that at the moment attention fails, this fluid is actually being expelled outward away from the brain. And when attention recovers, it’s drawn back in,” Lewis explains. The researchers interpret these events as an attempt by the brain to enter brief, sleep-like cleaning cycles to recover some lost restorative benefit, at the expense of sustained attention.
A unified circuit
The coordinated timing of neuronal changes, pupil responses, CSF flow, and cardiovascular shifts implies that attention lapses are not isolated brain events but body-wide phenomena. That tight coordination points to a central regulatory system that links high-level cognitive functions—like attention and perception—with fundamental physiological processes such as fluid dynamics and blood flow.
Although the study did not directly identify the neural circuit responsible, the authors note the noradrenergic system as a plausible candidate. This system, which releases the neurotransmitter norepinephrine, influences both cognitive state and bodily arousal and has been shown to oscillate during sleep.
Funding:
This research was supported by the National Institutes of Health, a National Defense Science and Engineering Graduate Research Fellowship, a NAWA Fellowship, a McKnight Scholar Award, a Sloan Fellowship, a Pew Biomedical Scholar Award, a One Mind Rising Star Award, and the Simons Collaboration on Plasticity in the Aging Brain.
Key Questions Answered:
A: Cerebrospinal fluid briefly flushes outward from the brain, mimicking the cleansing process seen during sleep and disrupting attention.
A: Researchers believe the brain attempts to compensate for missed restorative functions by entering brief, sleep-like cleaning cycles while awake, at the cost of attention.
A: The findings show that attention lapses and physiological cleansing are controlled by the same regulatory system, linking alertness to the brain’s need for recovery.
About this sleep and neuroscience research news
Author: Sarah McDonnell
Source: MIT
Contact: Sarah McDonnell – MIT
Image: Image credited to Neuroscience News
Original Research: Open access. “Attentional failures after sleep deprivation are locked to joint neurovascular, pupil and cerebrospinal fluid flow dynamics” by Laura Lewis et al., Nature Neuroscience. DOI: 10.1038/s41593-025-02098-8
Abstract
Attentional failures after sleep deprivation are locked to joint neurovascular, pupil and cerebrospinal fluid flow dynamics
Sleep deprivation quickly impairs cognitive function and, over time, contributes to neurological risk. The mechanisms linking lost sleep to declines in cognition are not fully understood.
Using simultaneous fast fMRI and EEG, the study examined how sleep deprivation alters cognitive performance together with neural and fluid dynamics in the human brain.
Results show that attentional failures after sleep loss are tightly coordinated with a sequence of brain–body changes, including neuronal shifts, pupil constriction, and CSF pulsations, indicating a coupled system that links fluid dynamics and neuromodulatory state.
CSF flow and hemodynamic changes are tied to attentional performance during wakefulness, with CSF pulsations following attentional impairment. The timing of these events is consistent with a vascular mechanism regulated by neuromodulatory activity.
These findings suggest that the cognitive costs of sleep deprivation reflect an underlying, hard-to-ignore need for restorative periods driven by a central neuromodulatory system that coordinates both neuronal function and fluid physiology.