We all recognize that lack of sleep hampers our concentration, but what’s the reason behind it? It may be that your brain is temporarily losing focus as it attempts to refresh itself.

During sleep, the brain undergoes a cleansing process where cerebrospinal fluid (CSF) circulates into the organs and drains out at the base of the brain. This cycle helps eliminate the metabolic waste that builds up during waking hours. If this doesn’t happen, brain cells could be harmed.

Laura Lewis and her team at the Massachusetts Institute of Technology theorized that the drop in alertness often seen after insufficient sleep could stem from the brain trying to make up for lost time while awake.

To test this theory, researchers enlisted 26 participants aged between 19 and 40 to first ensure they were well-rested. Two weeks later, they were kept awake overnight in a lab setting.

In both instances, the researchers recorded participants’ brain activity using MRI scans the next morning while they performed two specific tasks. During these tasks, participants needed to press a button every time they heard a particular sound or saw a cross on the screen transform into a square. This occurred many times over a span of 12 minutes.

As anticipated, participants struggled to hit the button significantly more often when sleep-deprived compared to when they were well-rested. This indicates that lack of sleep diminishes concentration capacity.

Notably, the analysis of the brain scans revealed that participants lost focus approximately two seconds before the CSF was expelled from the base of the brain. Additionally, the CSF was reabsorbed into the brain about one second after attention was regained.

“Think of the brain-cleansing process like a washing machine: you fill it with water, let it agitate, and then drain it. The loss of attention corresponds to the swirling phase,” Lewis explains.

The results imply that if the brain is unable to cleanse itself during sleep, it compensates while you’re awake, thus impairing concentration, according to Lewis. “If this wave of fluid flow doesn’t occur, because you were awake the entire night, your brain starts sneaking in this process during the day, but it comes at the price of your focus.”

While the exact reason for how this cleaning process affects attention remains unclear, pinpointing the specific brain circuits involved may help uncover strategies to mitigate the cognitive impacts of sleep deprivation, Lewis states.