Hard physical labor can wear you out, but what about hard mental labor? One feels tired when they sit around thinking hard for hours. According to the findings of the researchers, the reason you feel mentally exhausted is not solely in your head.
According to their studies, when a lot of cognitive work is done for a long time, the parts of the brain known as the prefrontal cortex can become toxic. The researchers explain that this changes your control over decisions so you shift to low-cost actions requiring no effort or waiting.
"Influential theories suggested that fatigue is a sort of illusion cooked up by the brain to make us stop whatever we are doing and turn to a more gratifying activity." "Our findings show that fatigue is a signal that makes us stop working, but for a different reason: to preserve the integrity of brain functioning."
Pessiglione and others wanted to understand what mental fatigue is. The brain is unable to compute continuously. They were interested in finding out why. They thought the reason had to do with the need to recycle toxic substances.
They used MRS to check brain chemistry over the course of a workday. Those who needed to think hard and those who had relatively easy cognitive tasks were looked at.
The group doing hard work was the only one that showed fatigue. The people in that group made a shift towards options with little effort. They had higher levels of glutamate in their brains. The authors say it supports the idea that cognitive control is more difficult after a mentally tough workday due to the fact that further activation of the prefrontal cortex is more expensive.
Is there a way to overcome this limitation of our brain's ability to think?
Pessiglione is afraid. Rest and sleep are good old recipes. There is good evidence that the brain doesn't use glutamate during sleep.
Other practical implications could be present. The researchers say that monitoring of prefrontal metabolite could help to detect mental fatigue. Work agendas can be adjusted to avoid burnout. People are advised to avoid making important decisions when they are tired.
They want to find out why the prefrontal cortex is susceptible to fatigue. They want to know if the same markers of fatigue in the brain can predict recovery from depression or cancer.
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