If you didn't sleep well the night before, it can be difficult to concentrate the next day. This may be because your brain is trying to refresh itself, causing a temporary loss of attention. The related research was published in *Nature Neuroscience* on October 29th.
During sleep, the brain undergoes a flushing cycle—cerebrospinal fluid is repeatedly flushed into the brain and then flows out from the base of the brain. This process clears away metabolic waste accumulated during the day, which could otherwise damage brain cells.
Difficulty concentrating may be a sign that the brain is "self-cleaning." Image credit: Jenny Evans
Laura Lewis and her colleagues at MIT wanted to know whether the inattention that often occurs when sleep-deprived might be the result of the brain trying to compensate for “self-washing” when awake.
To investigate this problem, scientists divided the experiment into two phases. In the first phase, 26 participants aged 19 to 40 were given a good night's sleep and sufficient rest. In the second phase, two weeks later, they were kept awake all night in the laboratory.
The day after each of the two phases of the trial, participants underwent a 12-minute test. During the test, they pressed a button each time they heard a specific tone or saw the cross on the screen change into a square. Simultaneously, the research team recorded their brain activity using an MRI scanner.
Unsurprisingly, compared to when they were well-rested, participants failed to press the button on time significantly more often when they were sleep-deprived, meaning that lack of sleep made it harder for them to concentrate.
Notably, when researchers analyzed the brain scans, they found that participants lost attention approximately two seconds before cerebrospinal fluid flowed from the base of the brain. More importantly, cerebrospinal fluid was flushed into the brain about one second after attention was regained.
Lewis said, "You can think of the brain's cleaning process as a working washing machine. First, you put water in, then the washing machine spins, and then the water is drained. So these periods of attention deficit that we studied are exactly the spinning process that happens."
The research suggests that when the brain cannot clean itself during sleep, it will do so while you are awake, which can affect concentration. "If you don't sleep at night, there's no flow of these fluids in your brain, so it will quietly clean itself during the day, at the cost of decreased concentration," Lewis said.
While the exact mechanisms by which this cleaning process leads to a loss of attention remain unclear, Lewis says that identifying the brain circuits that cause attention deficit could help develop methods to reduce the cognitive effects of sleep deprivation.
Related paper information: https://doi.org/10.1038/s41593-025-02098-8