On September 10, 1984, one of the most exciting chess games in history began between Garry Kasparov and longtime world champion Anatoly Karpov, who was 22 years older than him. Five months later, International Chess Federation President Florencio Campomanes stopped him without a winner, as both players were physically and mentally exhausted. But why should thinking cause fatigue?

French researchers think they know the answer. Mentally demanding activities produce certain chemicals that, while essential for proper brain function, are neurotoxic in high concentrations. To avoid this, the brain creates a feeling of fatigue that makes us give up on our efforts. The researchers asked 50 volunteers to complete various tasks for six and a half hours, the equivalent of a French work day. One group was given more difficult tasks than the other, while the research team studied the brains of both.

A study published in the journal Cell Biology found significant differences in brain function between the two groups of volunteers. Only those who performed very difficult tasks showed signs of mental fatigue. In the same group, higher concentrations of glutamine, which plays an important role in the regulation of mental functions and actions, were found in brain synapses in the dorsolateral prefrontal cortex. According to scientists at the ICM Brain Institute in Paris, who prepared the study, “the neurotransmitter glutamine, and not the one taken as a dietary supplement (monosodium glutamate), is released when information is exchanged in the brain. When its concentration exceeds a certain threshold, an area of ​​the brain does not function enough to prevent it from increasing further to neurotoxic levels. It is at this point that the brain tells us that it is tired.”