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in collaboration with
Dr Gérald Kierzek (Medical Director of Doctissimo)
Medical validation:
August 18, 2022
After a complicated day, we sometimes feel exhausted. But what is this mental fatigue due to? A new study published in the journal Cell (finally) reveals the answer.
After a long day at work, it is common to feel exhausted. A simple daily task like preparing dinner or doing homework can seem overwhelming. But why does our brain seem so tired, as foggy? Researchers may have found the answer. Explanations.
40 volunteers participated in the study
To try to understand the causes of this cognitive fatigue, the researchers recruited 40 participants, aged 21 on average. They were separated into two groups, based on their trait of impulsivity (Barratt Impulsivity Scale BIS-11) and their state of fatigue.
For more than six hours, the participants had to perform two cognitive tasks (N-switch and N-back). During these tests, a letter appeared every 1.60 seconds on the screen, colored in red or green. Participants then had to deliver a response in a short time (less than 0.8 seconds).
The scientists then measured the impact of performing these cognitive tasks deemed “difficult” compared to performing “easy” tasks. They also observed pupil movements (dilation) and glutamate concentration in a brain region of cognitive control (lPFC).
Results ? The group performing difficult cognitive tasks was more fatigued at the end of the experiment. He even ended the experiment with a higher amount of glutamate (the main excitatory neurotransmitter in the nervous system), compared to the control group.
” Our model assumes that the recruitment of cognitive control regions depletes certain metabolic resources or accumulates toxic by-products “, specify the researchers.
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Fatigue Causes the Brain to Choose “Low Effort” Actions
For the researchers, these results show that difficult cognitive work leads to an accumulation of glutamate in the lateral prefrontal cortex. However, the need for glutamate regulation reduces “decision-making” capacities.
” This “reduced control” favors choosing low-effort actions with short-term rewards “, specify the scientists.
This phenomenon would therefore partly explain the cerebral fatigue felt at the end of the day, and the consequences that follow: difficulty in making decisions and/or careless errors.
To fight against this mental fatigue, a few simple reflexes must be adopted: get some fresh air, eat a balanced diet, take a 20-minute nap every day, practice relaxation…