💤 When your brain activates its "night" program during the day

Have you ever felt particularly distracted after a night of too little sleep? That feeling of mental fog, where thoughts seem to slow down and concentration fades, could correspond to brain activity that shouldn't be occurring at that time of day. While our mind struggles to remain alert, processes usually observed during sleep seem to kick in.

Researchers at the Massachusetts Institute of Technology (MIT) recently observed what happens in our heads during these brief moments of inattention. Their study, published in Nature Neuroscience, reveals that when our attention wavers due to a lack of sleep, the cerebrospinal fluid that surrounds the brain performs movements similar to those that take place during the night. This mechanism, essential for clearing accumulated waste, thus appears while fully awake when rest has been insufficient.


During sleep, a fluid called cerebrospinal fluid circulates around the brain to cleanse it of residues produced during the day. This cleaning is important for maintaining brain functions in good condition. The MIT team found that when a person lacks rest, this same fluid begins to move during periods of wakefulness. These movements coincide with sudden drops in attention, as if the brain were trying to make up for lost time by activating a repair process at the wrong moment.

To reach these observations, scientists invited 26 volunteers to undergo two sessions in a laboratory: one after a night of sleep deprivation, the other after normal rest. The day after each session, participants performed attention tests while being monitored by brain imaging and physiological sensors. This approach allowed for the simultaneous measurement of brain activity, cerebrospinal fluid movements, as well as heart rate and breathing.

The results clearly show that performance drops when sleep is lacking. Responses to tests are slower, and sometimes visual or auditory signals are not even perceived. Each time attention weakens, the cerebrospinal fluid exits the brain and then returns when concentration resumes. Laura Lewis, a professor at MIT, indicates that these fluid waves, normally absent during wakefulness, appear linked to a compromise where the brain temporarily sacrifices attention to try to restore itself.

These episodes of distraction do not concern only the brain. The researchers noted that they are accompanied by changes throughout the body: breathing and heart rate slow down, and the pupils contract. These bodily changes begin about twelve seconds before the movement of cerebrospinal fluid, suggesting that close coordination exists between mental functions and basic physiological processes. A unique circuit might regulate both our ability to stay attentive and fundamental aspects like brain fluid dynamics.

Although the exact circuit responsible for this coordination remains to be identified, scientists mention the noradrenergic system as a likely candidate. This system, involved in regulating wakefulness and sleep, could explain how attention and bodily functions are so closely linked.