Sleep loss triggers brain fluid pulses that impair attention, study finds

By Hugo Francisco de SouzaReviewed by Susha Cheriyedath, M.Sc.Feb 16 2026

New neuroimaging research shows that when sleep-deprived people lose focus, the brain briefly shifts toward sleep-like physiology, offering fresh insight into why cognitive performance declines without adequate rest.

Study: Attentional failures after sleep deprivation are locked to joint neurovascular, pupil and cerebrospinal fluid flow dynamics. Image Credit: New Africa / Shuttertock

In a recent study published in the journal Nature Neuroscience, researchers investigated the precise physiological dynamics associated with transient attentional lapses during acute sleep deprivation rather than a broader clinical "brain fog" syndrome often observed during sleep deprivation. The multimodal study leveraged data from 26 healthy adults and found that when sleep-deprived individuals experience lapses in attention, their brains undergo a coordinated shift in physiology involving neural activity, blood flow, and pupil diameter.

Most notably, the study found that these lapses are synchronized with sleep-like large-amplitude low-frequency oscillatory cerebrospinal fluid (CSF) waves typically seen predominantly during sleep. The study therefore concludes that attention failures are not random errors or neural deficits but reflect coordinated brain–body state changes whose functional role remains uncertain, rather than a demonstrated attempt to activate metabolic waste-clearance systems.

Sleep deprivation, defined as poor-quality or insufficient sleep (7-9 hours for adults), is a pervasive issue in modern society, with clinically documented consequences ranging from reduced cognitive performance to increased risk of accidents.

While decades of research have established a causal relationship between insufficient sleep and "attention failures," defined as moments when an individual fails to respond to an obvious stimulus, the specific neural and physiological mechanisms driving these lapses remain debated.

Recent research has shown that during non-rapid eye movement (NREM) sleep, the brain exhibits large, rhythmic waves of CSF flow. Termed colloquially "brain washing," although these oscillations are bidirectional and not established as net waste-clearance flow, these processes are thought to help clear metabolic waste products and have previously been considered incompatible with wakefulness; however, this belief remains scientifically unverified.

Multimodal Within-Subject fMRI, EEG, and Pupillometry Study Design

The present study hypothesizes that the boundaries between sleep and wakefulness may blur in sleep-deprived subjects, allowing CSF dynamics to disrupt cognition even during apparent wakefulness. It tests this hypothesis through a multimodal study involving 26 healthy adults, with a mean age of 25.6 years.

The study employed a within-subjects design in which each participant was tested twice: once after a full night of rest and once after a night of total sleep deprivation monitored in a laboratory, thereby controlling for inter-participant variation.

Participants were required to perform a Psychomotor Vigilance Test (PVT) during which multiple physiological measurements were recorded. PVTs are standard, validated tasks that require sustained attention and rapid responses to visual or auditory stimuli.

The primary physiological measurements of interest included participants' blood oxygenation, hemodynamics, and CSF flow, measured using fast functional magnetic resonance imaging (fMRI). The study also measured electrical brain activity using electroencephalography (EEG) and pupil diameter using pupillometry.

Data analyses aimed to generate a second-by-second timeline of the physiological changes in the brain and body that accompany a participant’s attention failure.

CSF Oscillations, Pupil Constriction, and EEG Changes During Attention Failures

The study’s first major finding was that sleep-deprived participants displayed significantly slower reaction times and more frequent omissions and missed responses than when rested (P < 0.0001).

Analyses of physiological data further revealed that sleep-deprived subjects exhibited sleep-like, large-amplitude, low-frequency oscillatory CSF waves that intruded into wakefulness, rather than sustained directional fluid flow. The power of these fluid waves was statistically similar to that observed during N2 sleep (24.50 dB vs. 24.80 dB).

Approximately two seconds before the documented lapse, the participant’s attention abruptly declined. This lapse coincided with pupil constriction and was followed by a large-scale outward pulse of CSF. As the participant regained attention, the pupil dilated, and CSF was observed to flow back into the brain.

Pupil diameter and CSF demonstrated a correlation (r = 0.26). Pupil constriction, indicating low arousal and alertness, coincided with significant changes in brain blood volume. The authors hypothesize that these associations likely reflect a shared neuromodulatory arousal system with vascular mediation rather than a direct causal effect of pupil constriction on CSF movement.

Finally, EEG data obtained during attention lapses showed a substantial reduction in electrical brain activity, particularly in the alpha-beta range (10-25 Hz), which physiologically signals a momentary suppression of cortical excitability, alongside broader spectral changes consistent with transient low-arousal brain states.

Together, these findings suggest that the sleep-deprived brain physiologically mimics a state of "low arousal," usually reserved for sleep. This low-arousal state triggers coupled neurovascular and CSF oscillatory dynamics rather than a demonstrated fluid-clearing process, correlating with a significant drop in cognitive performance.

Mechanistic Interpretation and Public Health Implications

The present study provides evidence that attentional failures reflect coordinated brain–body state shifts potentially representing an intrinsic sleep-pressure signal rather than merely localized neural glitches, including changes in pupil diameter, vascular dynamics, and CSF pulsations.

The study concludes that these dynamics reflect a central neuromodulatory circuit, potentially involving the noradrenergic system, that modulates both alertness and brain fluid physiology. However, whether these CSF oscillations contribute to the clearance of metabolic waste or to other restorative functions remains unresolved. These findings support public health guidelines that emphasize the importance of sufficient, high-quality sleep.