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Thinking hard makes you tired, science says so

October 11, 2022
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Thinking hard makes you tired, science says so

If after a day of work that required attention and concentration you feel mentally tired and just want to sit in front of the TV and watch a comedy, indulge your brain's desire to rest. In fact, it is not a question of laziness, but of a real need for the body to regenerate itself and reduce the toxins that have accumulated in excess in the brain. In short, mental fatigue is a signal that should not be underestimated, as emerges from a very recent and very interesting scientific research published in the journal Current Biology by a group of French scientists (Wiehler et al, Current Biology, 2022).

Thinking hard makes you feel tired, but why?

Previous studies had already shown that intense and protracted intellectual activities lead to fatigue. It was initially thought that a great mental activity can lead to a reduction in blood sugar with a subsequent feeling of fatigue. However, no studies have ever been able to demonstrate this association as no results have ever been replicated.

Therefore, there must be another link between what happens in the brain and mental fatigue. This link appears to have been found by French scientists led by Dr Antonius Wiehler. But let's understand better.

Thinking too much causes toxins to accumulate in the brain, the study

Scientists have recruited 40 volunteers. The study participants were divided into two groups. The first group was asked to carry out, for 6 and a half hours, the equivalent of a working day, a repetitive but complex task on the computer. The second group performed a similar but less tiring task for 6 and a half hours. All groups, during the experiment, took two breaks of ten minutes each. At the end of the experiment, the group that had carried out the most complex task and that required greater mental effort was experiencing a higher level of fatigue. In particular, each subsequent decision made was aimed at reducing fatigue and preferring less gratification following less effort rather than greater gratification following greater effort. During each decision, the group that performed the most difficult tasks had a reduction in pupil dilation, which, as explained by the study authors, is a condition related to a lower level of exertion. In short, the brain had put in place everything in its power to rest and engage in activities that required less effort. The explanation of what was observed was always provided by the same research group who, at the end of the working day, subjected all the volunteers to functional magnetic resonance imaging tests. Well, what emerged was that those who had carried out the most strenuous tasks on a mental level had an accumulation of glutamate in the prefrontal cortex, the area of the brain involved in cognitive processes including the ability to make decisions. Glutamate, in addition to being present in various foods to increase their flavor, is also a neurotransmitter in the central nervous system that, however, if at high levels, becomes toxic. In short, when glutamate levels exceed the limits due to intense mental effort, then the brain puts in place processes whereby the activation of the prefrontal cortex is limited, in order to restore the right glutamate levels.


As indicated by the authors of the study, taking breaks during work, ensuring after the effort moments of rest and a good sleep is important to cleanse the brain of toxins. Not only that, this research also deduces that the best time to make important decisions is when you are rested, and not after a day of work. However, the research continues and scientists will try to understand how rest can regenerate the brain, indicating how many breaks during work and how many hours of sleep are needed to reduce glutamate levels. We expect to answer these questions in the near future. For the moment, we know that after intellectual work, if we feel tired and exhausted and unable to undertake complex activities, it is not a signal that we are lazy but that our brain is intoxicated. So you need to listen to it and take a break!

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