A long day of hard thinking can sometimes feel as exhausting as a day of manual labor, and experts say they know why.
A new study has found that people may feel fatigued after intense mental work because it causes toxic byproducts to build up in the prefrontal cortex part of the brain.
This changes a person’s ability to control decisions, so they turn to effortless actions or wait when mental fatigue sets in.
Fatigue is a way of telling the brain to shut down to save itself.
Mathias Pessiglione of the University of Pitie-Salpetriere in France, said: “Influential theories suggest that fatigue is a kind of illusion cooked by the brain to make us stop whatever we’re doing and move on. to a more satisfying activity.
“But our findings suggest that cognitive work leads to a real change in function – a build-up of toxic substances – so fatigue would actually be a signal that stops us from working, but because another purpose: to maintain the integrity of brain activity.”
The scientists tracked brain chemistry over a day’s work in two groups of people – those who needed to think a lot and those with relatively easier cognitive tasks.
In the first group, they observed signs of fatigue, including decreased pupil dilation, and those in that group made short-term choices for reward proposals with little to no expense. much effort.
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The researchers added that this group had higher levels of a chemical called glutamate in the prefrontal cortex.
This, they say, supports the theory that glutamate accumulation makes it so expensive to activate this extra part of the brain, that cognitive control becomes more difficult after a stressful day at work.
The findings have been published in the journal Current Biology.