World Day

Lack of sleep 'protects' the brain: why we do not concentrate after a sleepless night

During wakefulness, sleep-like phenomena appear with reduced attention and reactions: a study in Nature Neuroscience shows the importance of cerebrospinal fluid

by Federico Mereta

12 March 2026

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3' min read

Translated by AI

Versione italiana

3' min read

Translated by AI

Versione italiana

We have known this for a long time. To improve memory, there is one ingredient that cannot be missed. It is sleep, satisfying in quantity and quality. If we sleep well, the brain not only fixes memories better but also sets in motion recovery and physiological 'cleansing' processes, useful both in retaining the information that counts and in eliminating the waste accumulated during wakefulness.

However, limiting the action of a good night's rest to the mere depositing of memories is reductive. Because when we are deprived of necessary rest, that same cerebral 'cleansing' moves along the hands of the clock: and after sleep deprivation, attention can collapse.

In practice, you 'switch off' during a meeting or fail to carry out a complex task.

Because the brain preserves itself. And so it gives up concentrating. Finally explaining what happens when you struggle to stay 'alert' is original research that shows why after a night when you have had little to no rest it becomes more difficult to stay focused, with thoughts wandering and reaction times lengthening.

The study, published in Nature Neuroscience, was conducted by experts from MIT (Massachusetts Institute of Technology) and was coordinated by Laura Lewis and Zinong Yang.

The action of cerebrospinal fluid

What happens when concentration suddenly drops causing daytime sleepiness? "According to research, the momentary drop in attention is associated with pulsations of the cerebrospinal fluid, with a phase of outward flow followed by re-entry," explains Lino Nobili, Director of Child Neuropsychiatry at the Gaslini Institute in Genoa, lecturer at the University of Genoa and President of the Italian Sleep Academy. "This reaction occurs normally during sleep and appears important for eliminating waste.

The authors hypothesise that, after sleep deprivation, episodes of spinal fluid dynamics typical of nocturnal rest emerge during wakefulness, as if trying to recover at least part of the lost rest'.

The Studio

In the end, however, it is precisely the drastic reduction in attention that ensues. After discovering in a 2019 study that fluid moves in a rhythmic pattern during sleep, which is closely correlated with changes in brainwave activity, experts tried to understand then what sleep interruption entails.

The study examined 26 volunteers observed both after a night of sleep deprivation in the laboratory and one after being well rested. Thus, the effects of sleep loss were assessed.

In the experiment, the subjectswore an electroencephalogram helmet to monitor brain activity while resting inside a functional magnetic resonance imaging machine to monitor both blood oxygen levels and the movement of cerebrospinal fluid in and out of the brain.

Heart rate, respiratory rate and pupil size were also recorded.

The brain's compensation

Participants completed two attention tests within the scanner, one visual and one auditory. In the visual task, they observed a fixed cross on a screen that occasionally turned into a square. They were asked to press a button each time the change occurred. In the auditory task, the visual signal was replaced by a sound.

After sleep deprivation, participants performed significantly worse than when they were well rested, with much slower reactions. Not only that.

When these brief lapses in attention occurred, it was seen that thecerebrospinal fluid tended to move outwards, only to flow back in once attention was restored.

'In summary, according to the study authors, the pattern would reflect the brain's attempt to compensate for lost sleep by activating a cleaning process that normally occurs at night, even if this temporarily interrupts attention,' Nobili reports.

Body involvement

Limiting the impact of sleep deprivation to the nervous system alone, however, is probably reductive.

Indeed, research shows thatdrops in attention are linked to changes that also involve breathing and heart rate, which slow down, and pupils that shrink.

The constriction of the pupils only slightly anticipates what happens in the cerebrospinal fluid. According to Lewis, as reported in a note, 'this suggests that there is a close co-ordination of these systems, so when attention fails, it may be felt perceptually and psychologically, but it also reflects an event occurring throughout the brain and body'.

"One way to think about these events is that because the brain needs sleep so badly, it does its best to enter a sleep-like state to restore some cognitive functions," Yang reports. "The brain's fluid system tries to restore function by pushing the brain itself to switch from states of high attention to states of high flow.