An MIT-led study finds that brief lapses of attention when we're tired coincide with waves of cerebrospinal fluid (CSF) moving out of the brain — the same cleaning process that occurs during sleep. In tests with over two dozen volunteers, sleep-deprived participants were slower on two attention tasks and sometimes failed to show expected brainwave responses. Researchers propose the tired brain alternates between high-attention and high-flow (cleaning) states, trading momentary focus for partial restoration.
When You're Tired, Your Brain Briefly 'Cleans' Itself — and You Lose Focus
An MIT-led study finds that brief lapses of attention when we're tired coincide with waves of cerebrospinal fluid (CSF) moving out of the brain — the same cleaning process that occurs during sleep. In tests with over two dozen volunteers, sleep-deprived participants were slower on two attention tasks and sometimes failed to show expected brainwave responses. Researchers propose the tired brain alternates between high-attention and high-flow (cleaning) states, trading momentary focus for partial restoration.
11:56, 02.11.2025Science
When You're Tired, Your Brain Briefly 'Cleans' Itself — and You Lose Focus
A recent MIT-led study sheds light on what happens in the brain during short episodes of zoning out caused by sleep loss. Researchers report that brief lapses of attention coincide with waves of cerebrospinal fluid (CSF) moving outward from the brain — the same flushing motion that normally occurs during sleep to clear metabolic waste.
Investigators propose that when people are sleep deprived, the brain attempts to compensate for missed overnight cleaning by triggering bursts of CSF flow while awake. That compensatory flushing appears to come at an attentional cost: the moments when CSF flows are associated with transient failures of focus.
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.
Laura Lewis, an associate professor at MIT and senior author of the study, led a team that compared brain activity after a restful night versus after a night with insufficient sleep. The researchers recruited over two dozen volunteers and tested them on two different attention tasks.
Sleep-deprived participants had slower response times and, in some cases, failed to show expected brainwave responses to stimuli — indicating brief lapses of attention. The team observed that these lapses coincided with outward CSF flow; attention recovered as the CSF was drawn back in.
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.
Zinong Yang, the paper's lead author and an MIT postdoctoral associate, says the findings imply the sleep-deprived brain partially shifts into a sleep-like mode to regain certain cognitive functions, oscillating between high-attention and high-flow states.
Why it matters: This work provides a plausible mechanism linking sleep loss with momentary lapses in attention, which could be important for safety-critical work and for understanding cognitive risks of chronic sleep deprivation. Further research will be needed to confirm long-term consequences and to explore whether interventions can reduce these wakeful CSF intrusions.