Have you ever felt mentally drained? Overloading our minds with worries or planning tasks to do causes tiredness, and it seems that this has a scientific explanation, since a study has found that doing intense cognitive work for hours causes potentially toxic by-products to accumulate in the prefrontal cortex of the brain, and that as a consequence the control of decisions is altered.
Mental exhaustion would actually be a defense mechanism of the brain with the aim of protecting its functions and the new research, which has been published in Current Biology, reveals that as cognitive fatigue develops, the brain switches to tasks that do not require effort to get it.
“Influential theories have suggested that fatigue is a kind of illusion concocted by the brain to get us to stop what we’re doing and move on to a more rewarding activity,” says 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”.
If you are tired, do not make important decisions
The researchers wanted to find out what mental fatigue really is and why the brain, unlike machines, cannot be constantly doing calculations. They suspected that the cause had to do with the need to recycle potentially toxic substances that are generated from neuronal activity. They used magnetic resonance spectroscopy (MRS) to monitor brain chemistry during a working day to see if their hypothesis was true. They performed the tests on two groups of individuals: those who needed to think a lot and those who had relatively simpler cognitive tasks.
“Fatigue would be a signal that makes us stop working to preserve the integrity of brain function”
They only observed signs of fatigue – including decreased pupil dilation – in the group of those who had a hard job. These people also saw a shift in their choices toward options that offered short-term, low-effort rewards. In addition, they also had higher levels of glutamate at synapses in the brain’s prefrontal cortex. According to the authors, this supports the idea that glutamate accumulation makes further activation of the prefrontal cortex more costly and cognitive control more difficult after a mentally taxing workday.
These scientists have pointed out that we cannot avoid this limitation in our brain’s ability to think hard, although Pessiglione advises: “I would use good old recipes: rest and sleep! There is good evidence that glutamate is cleared from synapses during sleep.” They also make a good recommendation: that people avoid making important decisions when they are tired.
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