tired after thinking too much?

Perhaps you have already felt this particular fatigue. You have an overwhelming urge to lie down on the sofa after hours of concentration. Yet: you have been sitting all day. You suffer from cognitive fatigue. Nothing surprising or pathological about it – it’s a natural process. But how can you feel so exhausted without making any physical effort? French researchers have studied an interesting track: the answer would lie in the levels of glutamate in the brain.

>> Good or bad memory? Molecules decide

A molecule responsible for cognitive fatigue

Neuroscientists from the Institut du Cerveau (ICM) wanted to test whether cognitive fatigue could be the result of metabolic changes in the brain. For this they asked 24 volunteers to carry out a difficult task. The exercise is to observe the letters that appear every 1.6 seconds on a screen and identify when one of them matches a letter that appeared three letters earlier. Sixteen other volunteers performed a similar but easier task. Both groups worked for six hours, with two 10-minute breaks.

During this time, the researchers measured the levels of glutamate present in the volunteers’ lateral prefrontal cortex. This brain region is known to handle self-control and helps us curb impulses. Glutamate is a molecule that can disrupt brain function if present in large quantities.

However, the researchers noted that glutamate had accumulated in the brains of the participants performing the more difficult task. Also, at the end of the day, they opted for an immediate reward, rather than a larger reward that would come several months later. As if cognitive fatigue diminished their ability to control their impulses.

How to recover from fatigue after mental effort?

These findings tend to show a link between cognitive fatigue and neuronal metabolism. If high levels of glutamate in the lateral prefrontal cortex are synonymous with exhaustion, how could they be regulated after a concentration effort? ” It would be nice to know more about how glutamate levels are restored. Is sleep useful? How long do the breaks have to be to have a positive effect? ยป, Raises Antonius Wiehler, researcher at the Paris University Hospital Group psychiatry & neurosciences.

Answers that may have interesting applications. Especially for some workers whose jobs require intense and prolonged concentration.

It remains to be seen which molecular mechanisms are responsible for the accumulation of glutamate in the brain during brain exertion. Future studies could be conducted on an animal model, in which glutamate levels could be artificially altered in the brain.

From now on, if after a hard day’s work you just want to sit in front of your favorite series, don’t feel guilty anymore!

Source: Current biology, August 2022.

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