New fatigue study shows why a day of intense thinking is so tiring Science and technology news

A long, hard day of reflection can sometimes feel as tiring as a day of physical labor, and experts think they know why.

A new study has found that people can feel tired after intense mental work because of potentially toxic byproducts building up in the prefrontal cortex part of the brain.

This changes a person’s control over decisions so that it shifts toward actions that don’t require effort or waiting when mental exhaustion sets in.

The fatigue is a way of telling the brain to shut down to save itself.

Mathias Pessiglione, from the Pitie-Salpetriere University in France, said: “Influential theories have suggested that fatigue is a kind of illusion cooked up by the brain to make us stop whatever we are doing and become one turn to more satisfying activity.

“But our results show that cognitive work leads to a real functional change – the accumulation of harmful substances – so that fatigue would actually be a signal that compels us to stop working, but for a different purpose: the integrity of brain function too.” maintain.”

The scientists monitored brain chemistry over a work day in two groups of people – those who needed to think hard and those who did relatively easier cognitive tasks.

In the first group, they observed signs of fatigue, including reduced pupil dilation, and people in this group made low-effort decisions on options that suggested a short-delay reward.

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The researchers added that this group had higher levels of a chemical called glutamate in the prefrontal cortex.

They say this supports the theory that glutamate accumulation makes further activation of this part of the brain costly, so much so that cognitive control becomes more difficult after a mentally hard day’s work.

The results were published in the journal Current Biology.