Mental fatigue can intoxicate the brain, study finds

It’s not just physical exertion that can cause fatigue. Spending many hours thinking, performing some cognitive activity, can also lead to exhaustion. A study published in the scientific journal Current Biologyprovides some evidence of why we feel mental fatigue.

According to the researchers, intense and prolonged cognitive work, which lasts between four and five hours, makes potentially toxic substances build up in the part of the brain known as the prefrontal cortex. The result of this? O decision control is changedmaking you involuntarily look for paths that require less effort, as cognitive fatigue sets in.

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According to researcher Mathias Pessiglione, one of the authors of the study, the findings of the work show that fatigue is not an “illusion” invented by the brain to make us stop what we are doing and return to more pleasurable activities, according to previous theories. Instead, “cognitive work results in a real functional change, with accumulation of harmful substances”.

“So, fatigue would in fact be a signal that would make us stop working, but with a different purpose: to preserve the integrity of the brain’s functioning”, completes the researcher, from the Pitié-Salpêtrière University in Paris, France, in a statement. .

How was the study done?

The study authors wanted to understand why the brain is not able to engage in cognitive activities without pauses. Scientists suspected that the organ needed to recycle potentially toxic substances that arise from neural activity. The aim of the study was, then, to evidence this theory.

To do this, the researchers used magnetic resonance spectroscopy to monitor brain chemistry over the course of a working day. They analyzed two groups of people: the first was made up of workers who needed to think a lot to do their job, while the second was made up of those who had relatively easier cognitive tasks.

Among those who worked hard mentally, it was possible to notice signs of fatigue, such as reduced pupil dilation. Members of this group also chose tasks that offered short-term rewards with little effort.

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In addition, they also showed higher levels of glutamate (a fundamental neurotransmitter in the mechanism of some neurodegenerative diseases) in the synapses, the region where the nerve impulse from the prefrontal cortex of the brain is transmitted.

According to the authors, this supports the idea that glutamate buildup can make cognitive control difficult after a mentally difficult day at work. For Pessiglione, there’s not much to do in this situation other than good old-fashioned rest. “There is good evidence that glutamate is cleared from synapses during sleep,” said the researcher.