Mental fatigue: how thinking too much makes you feel tired

La fatiga mental es la alteración temporal o la disminución de la eficiencia funcional mental y física.

Mental fatigue is the temporary alteration or decrease in mental and physical functional efficiency.

Photo: Yana Iskayeva/Shutterstock

Although overthinking does not require any apparent physical effort, you will usually find that as you think more, symptoms such as decreased attention and concentration, general tiredness, itchy eyes, dizziness, headaches and even an irritable emotional state appears.

These are the characteristics of the mental fatigueinitially defined as temporary alteration or decrease in mental and physical functional efficiency. For this reason, a group of scientists in France joined efforts to find the reasons that originate it.

Their studies, published on August 11 in the journal Current Biologyshow that when intense cognitive work continues for several hours, it causes the buildup of potentially toxic byproducts in the part of the brain known as the prefrontal cortex.

According to the researchers, this in turn alters your control over decisionsso it switches to low-cost actions that require no effort or waiting as cognitive fatigue develops.

“Influential theories suggested that fatigue it is a kind of illusion invented by the brain so that we stop doing what we are doing and move on to a more rewarding activity”, explained Mathias Pessiglione of Pitié-Salpêtrière University in Paris, France.

“But our findings show that cognitive work results in a true functional alteration, the accumulation of harmful substances, so fatigue would be a signal that makes us stop working, but with a different purpose: to preserve the integrity of the functioning of the brain. brain,” he said.

The aim of the studies was primarily to understand what mental fatigue actually is, since while machines can continuously calculate, the brain cannot. They wanted to find out why. They suspected that the reason had to do with the need to recycle potentially toxic substances that originate from neuronal activity.

To search for evidence to support this theory, Pessiglione and colleagues, including study first author Antonius Wiehler, used magnetic resonance spectroscopy (MRS) to monitor brain chemistry over the course of a workday.

In this way, they studied two groups of people: those who needed to think a lot and those who had relatively simple cognitive tasks.

They saw signs of fatigue, including reduced pupil dilation, only in the group that did intense mental work. Those in that group also exhibited in their choices a shift toward options that offered rewards in a short time with minimal effort.

critically, too they had higher levels of glutamate at synapses in the brain’s prefrontal cortex. This substance works as most abundant excitatory neurotransmitter in the brain, and glutamatergic neurotransmission regulates motor, sensory, and cognitive systems.

Recommendations to avoid mental fatigue

According to Pessiglione, there is no way to overcome this limitation on our brain’s ability to think hard. “I would use good old recipes: rest and sleep! There is good evidence that glutamate is cleared from synapses during sleep.”

Pessiglione also advises people to avoid making important decisions when they’re tired and to adjust work schedules to avoid burnout.

In future studies, the researchers hope to learn why the prefrontal cortex seems especially susceptible to glutamate buildup and fatigue. They are also curious whether the same markers of fatigue in the brain can predict recovery from health problems, such as cancer or depression.

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