A recent study from MIT sheds light on the brain's response to sleep deprivation, revealing that lapses in attention may coincide with the movement of cerebrospinal fluid (CSF) out of the brain. Laura Lewis, a professor at MIT, is the senior author of the study published in Nature Neuroscience, with Zinong Yang, a visiting graduate student, as the lead author.
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The researchers found that when individuals lack sleep, their bodies attempt to compensate for the brain's cleansing process typically occurring during sleep by initiating CSF flow. However, this compensation is accompanied by impaired attention. "If you don’t sleep, the CSF waves start to intrude into wakefulness where normally you wouldn’t see them, but they come with an attentional tradeoff," Lewis explained.
Despite the known importance of sleep for cognitive functions, the specific reason it is essential remains unclear. Lewis’s earlier research indicated that CSF flows in a rhythmic pattern during sleep, helping to eliminate waste accumulated throughout the day. This prompted her to investigate what happens to CSF flow during sleep deprivation.
The study involved 26 volunteers who were evaluated under two conditions: after a night of sleep deprivation and following well-rested nights. During testing, participants wore electroencephalogram (EEG) caps to monitor brain waves while in a functional magnetic resonance imaging (fMRI) scanner to measure both blood flow and CSF dynamics.
Participants performed visual and auditory attention tasks, where sleep-deprived individuals showed significantly poorer performance compared to their well-rested counterparts. Researchers observed CSF flowing out of the brain during moments of decreased attention. "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," noted Lewis.
The study identified accompanying physiological changes during attentional lapses, such as decreased heart rate and pupil constriction. Notably, pupil constriction preceded CSF flow by about 12 seconds, indicating coordination between brain activity and bodily responses.
The researchers propose that these findings point to a unified circuit managing both cognitive functions and basic physiological processes. They emphasize the need for further exploration into the circuits involved, with a focus on the noradrenergic system, known for regulating many functions via the neurotransmitter norepinephrine, which oscillates during normal sleep.
The research was supported by various grants, including those from the National Institutes of Health and several prestigious fellowships.