Cognitive fatigue, a signal that warns your brain of the risk of overheating

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Even professional chess players, after four or five hours of play, can start making big mistakes. Don’t you feel exhausted after a day of intense intellectual effort? This cognitive fatigue, far from being a mere invention of the mind, is based on physiological foundations. This is revealed by a French study, published on August 11 in Current Biology. Intense and prolonged mental effort actually causes a byproduct of neuronal activity, glutamate, to build up in certain areas of the lateral prefrontal cortex, a region that governs our higher mental functions. However, this excess glutamate disrupts the functioning of our neurons. “This fatigue would therefore be a signal that pushes us to stop working to preserve the integrity of our brain’s functioning”, summarizes Mathias Pessiglione, neuroscientist at the Brain Institute (ICM, Pitié-Salpêtrière hospital, in Paris) , who coordinated this work. work Therefore, it does not come, as has long been believed, from a depletion of glucose resources provided by the bloodstream. The Parisian team recruited 40 volunteer participants (20 men and 20 women), mostly students, with an average age of 24. They were randomly divided into two groups: the first had to perform cognitive tasks that required an intense effort of attention and the second the same type of tasks but easier (control group). These tests lasted six and a quarter hours, “with a break of ten minutes halfway through”, specifies the researcher. Increase in glutamate concentration First example of tests: the “n-back” task. Participants must indicate whether the last letter in a list matches the letter presented n previous positions (eg, FBLB shows a “2-back” match and BFLB a “3-back” match). Those in the control group did the test in “1-back” and those in the tested group in “3-back”, a much more difficult test. Another example is the “n-switch” task. Here, the rule depends on the color of the presented letter. If it is red, the participant must say whether it is a consonant or a vowel. If it’s green, if it’s uppercase or lowercase. As the letters moved, their color alternated much more frequently in the tested group, thus undergoing a more arduous test. The tests were divided into 5 sessions of 75 minutes. The researchers compared the two groups to each other, but also, within each group, what was going on in the minds of the participants between the beginning and the end of the tests. During sessions 1, 3, and 5, participants actually performed these tests in the tunnel of a magnetic resonance imaging (MRI) machine. While a conventional MRI measures blood flow through the brain (a reflection of which brain regions are working), here the researchers used another data acquisition technique: magnetic resonance spectroscopy, which measures concentrations of different substances in the brain. This technique also makes it possible to analyze the diffusion of these substances over short distances. “If a molecule has been released into the synapses [les espaces entre les neurones], it will spread much more easily than if it were confined inside the cells”, explains Mathias Pessiglione. You have 49.67% of this article left to read. The following is for subscribers only.
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