As the saying goes, "sleep is the best medicine," sleep is directly tied to health. Even missing a single night's sleep leaves the mind foggy and attention impaired the next day. The risk of accidents while driving rises and it can threaten life. A study found that this sequence of events is related to brain cleaning.
A team led by Laura Lewis, a professor in the Department of Electrical Engineering and Computer Science at MIT, said in the international journal Nature Neuroscience on the 29th (local time) that "sleep deprivation and reduced concentration are influenced by cerebrospinal fluid."
Cerebrospinal fluid is the liquid that surrounds the brain and spinal cord. While we sleep, the body uses cerebrospinal fluid to clear waste that has built up in the brain. The MIT team explained that when sleep is lacking, the brain is cleaned belatedly during the day, and attention declines in the process.
The researchers ran an experiment with 26 people ages 19 to 40. First, they slept sufficiently at night. A few days later, they were kept awake through the night. Participants wore glasses that record eyelid movements. If participants kept their eyes closed for more than 2 seconds, the researchers woke them. When participants slipped into a hypnagogic state with their minds growing dim, they chatted with them or took a light walk.
The next morning, participants took an attention test. They pressed a button when a specific sound played or the screen shape changed. When participants failed to sleep at night, they could not focus on the sounds and the screen and missed the button presses.
At the same time, the participants' brains were analyzed with functional magnetic resonance imaging (fMRI). When a specific brain region activates, blood flows to that area. fMRI shows the area in the brain image as if a light has turned on. When participants' attention dropped, cerebrospinal fluid flowed out toward the brain's base and removed waste. When attention recovered, cerebrospinal fluid flowed in.
The researchers explained, "When you cannot fall asleep at night, cerebrospinal fluid cleans the brain while you are awake the next day, and attention is reduced by that much," adding, "Cerebrospinal fluid and bodily changes are tightly coordinated."
References
Nature Neuroscience (2025), DOI: https://doi.org/10.1038/s41593-025-02098-8