Someone can get tired of not only manual work, but also a lot of thinking. Concentration and mental work for several hours also create a feeling of exhaustion, according to French scientists who have found new evidence to explain why this happens.

As they point out, feeling tired due to intense thinking is not something imaginary that exists only in the mind, but something very real and caused by the accumulation of “toxins” in the brain.

Researchers led by Dr. Matthias Pescillon of the Pitiers-Salpêtrière University in Paris, who published a related publication in the biological journal Current Biology, found that long hours of cognitive work create toxic by-products (mainly glutamate) in the body. prefrontal cortex.

This, in turn, leads to changes in the control over one’s decisions, with the result that the person gradually moves into activities with low “cost”, which do not require much effort.

“Influential theories have previously argued that this fatigue is a kind of illusion created by the brain to stop what we are doing and switch to more rewarding activities. But our results show that cognitive work leads to real functional changes, the accumulation of toxic substances, as a result of which the feeling of fatigue is a signal that will make us stop thinking, but for a different reason: to maintain the integrity of the brain. Pesiglione said.

While machines can continuously perform calculations, the human brain cannot. His fatigue is linked to the need to process toxic substances resulting from the cognitive activity of neurons, according to a new study that recorded the chemical composition of the brain during the day using magnetic spectroscopy.

Two groups of people were examined: those who thought intensely and those who thought freely. Signs of fatigue, such as decreased pupillary dilation, were only seen in the first group, which did a lot of thinking. People in the same group also had higher levels of glutamate in the synapses of the prefrontal cortex. The accumulation of glutamate makes cognitive control more difficult after much thought.

The “antidote” for feeling brain fatigue, according to researchers, is “rest and sleep.” They even recommend avoiding important decisions when a person is tired after hard mental work.