Fatigue after a period of mental work is not only psychological. French researchers, whose work is published in August 2022 in Current Biologyhave identified what is happening in the brain at this time.
When mental work leads to cognitive fatigue, increased effort becomes necessary to continue to exert cognitive control. Decisions then tend to become more impulsive.
The origins of this fatigue are hotly debated. Antonius Wiehler, from Sorbonne Universities, and his colleagues (1) proposed that the cost in effort would be linked to the need to recycle potentially toxic substances accumulated during the effort of cognitive control.
They validated this hypothesis using brain imaging technology to monitor brain metabolites throughout the rough equivalent of a workday during which two groups of participants performed tasks requiring cognitive control. high or low demand, interspersed with economic decisions.
The fatigue markers that were related to the quality of choices during economic decisions were present only in the group that underwent a high demand for cognitive control. Participants then had a preference for short-time, low-effort options. (After a day of mental work, financial decisions become more impulsive – Decision fatigue causes doctors to prescribe more antibiotics as the day progresses)
At the end of the day, high-demand cognitive work resulted in higher concentration and release of glutamate in a brain region of cognitive control, the lateral prefrontal cortex, compared to low-demand cognitive work and another brain region. little involved in cognitive work (the primary visual cortex).
Glutamate is the most important excitatory neurotransmitter in the central nervous system. A neurotransmitter is said to be excitatory when it increases communication between neurons.
Combined with previous imaging data, “
these results support a neuro-metabolic model in which glutamate accumulation triggers a regulatory mechanism that makes activation of the lateral prefrontal cortex more costly, explaining why cognitive control is more difficult to mobilize after a hard day’s work“, conclude the researchers. (Without the “reset” that sleep allows, the brain becomes hyperconnected and saturated)
For more information, see the links below.
(1) Francesca Branzoli, Isaac Adanyeguh, Fanny Mochel, Mathias Pessiglione.
Psychomedia with sources: Cell Press, CurrentBiology.
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