A new American study has identified the biological reason behind poor concentration during the day following a night of insomnia or insufficient sleep. Researchers found that when the brain is deprived of adequate rest, it shifts into a “waste-clearing” mode during waking hours — a process that normally occurs during deep sleep — ultimately undermining alertness and focus.
The research team from the Massachusetts Institute of Technology (MIT) discovered that after a restless night, the brain activates its internal cleansing system during the day. This system relies on the movement of cerebrospinal fluid, which helps flush out metabolic waste generated by daytime neural activity. Under normal conditions, this process takes place during deep sleep, when it does not interfere with cognitive functions.
However, the study found that when an individual does not get enough sleep, the brain attempts to perform this vital cleaning function while awake. The sudden movement of cerebrospinal fluid during periods of wakefulness disrupts attention and reduces mental efficiency.
To examine the phenomenon, researchers conducted experiments on 26 volunteers. Participants underwent concentration tests and MRI scans twice: once after a full night’s sleep and once after being sleep-deprived overnight.
The results showed that participants responded more quickly to visual and auditory cues when well-rested. In contrast, following sleep deprivation, their reaction times slowed significantly, and in some cases they failed to register certain signals altogether.
Laura Lewis, Assistant Professor at MIT and lead researcher on the study, explained: “When sleep is lacking, waves of cerebrospinal fluid begin to interfere with wakefulness.” She added that “attention weakens during the moments when these fluid waves flow through the brain.”
