Accumulation of toxic substances in the prefrontal cortex the brain undergoes intensive work, is responsible for the physical exhaustion caused by heavy mental work, According to a study by a group of scientists published in the journal Current Biology.
“Our results show that cognitive performance leads to true functional changes, the accumulation of harmful substances,” said Matthias Pessillone, a researcher at the Universite Pitié-Salpêtrière in Paris.
Thus, while “influential theories” claim that “fatigue is a kind of illusion concocted by the brain to make us stop doing what we do and move on to more rewarding activities,” it is now thought to also be “the signal that makes us stop working” in order to “preserve the integrity of the brain’s functioning,” the researcher said.
The result of mental work is a true functional change, the accumulation of harmful substances.
This is the scientific explanation for why not only hard physical work is tiring, but sitting for many hours in heavy thinking also causes fatigue. Scientists noticed that after intense mental work, they preferred to switch to activities that brought rewards in a short time and with little effort.
They also had higher levels of glutamate (one of the most important neurotransmitters in the nervous system) at the synapses in the prefrontal cortex. This makes further activation of the prefrontal cortex more costly, so cognitive control becomes more difficult after a mentally hard day at work. Thus, control over decisions is changed and the person is more likely to perform low-cost, effortless activities. As Pessillone explained, there is no way to avoid this, and the only recipe is to rest and sleep.
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In future studies, the researchers hope to learn why the prefrontal cortex seems to be particularly susceptible to glutamate accumulation and to investigate whether the same fatigue markers in the brain can predict recovery from health problems such as depression or cancer.