Scientists discover hints that may clarify why we experience fatigue after intellectually taxing activities

According to a recent study published in Current BiologyTrusted Source, the buildup of the neurotransmitter glutamate in the prefrontal cortex is linked to mental weariness.

Due to the need to remove excess glutamate due to its possibly harmful effect, mental work may need more effort, which could lead to exhaustion. Understanding the mechanics underlying the sensation of mental fatigue is advanced significantly by this.

Author of the study and psychologist at Pitié-Salpêtrière University Hospital’s Paris Brain Institute, Dr. Antonius Wiehler, explained to Medical News Today why they decided to investigate this particular subject:

“Nobody knows what mental fatigue is, how it is generated and why we feel it. It has remained a mystery despite more than a century of scientific research. Machines can do cognitive tasks continuously without fatigue, the brain is different and we wanted to understand how and why.”

“Besides, mental fatigue has important consequences: for economic decisions, for management at work, for education at school, for clinical cure, etc.,” he added.

After a day of engaging in demanding activities requiring mental effort or cognitive control, it’s natural to feel exhausted.

Inhibiting automatic or impulsive behaviours, cognitive control refers to mental or cognitive processes that enable an individual to modify their thoughts and behaviours in accordance with their aims. For instance, exercising cognitive control is necessary to pursue the long-term objective of maintaining a healthy weight.

People who are experiencing cognitive tiredness may find it harder to maintain cognitive control, which makes them more likely to act impulsively and seek out instant satisfaction.

The lateral prefrontal cortex is one of the brain areas that scientists have previously identified as being important in cognitive regulation and fatigueReliable Source (LPFC). One of the brain areas that exhibits greater activation when undertaking tasks requiring cognitive control is the LPC. Furthermore, prior research has demonstrated a reduction in LPFC activity with escalating mental or cognitive weariness. Trusted Source

But the cause of this feeling of weariness following lengthy cognitive effort tasks is still a mystery.

After a day of mental labour, it has been hypothesised that the brain may lack the energy resources required to exercise cognitive control due to the depletion of overall energy reserves, such as blood glucose levels. However, research indicates that cognitive tasks do not have an impact on total energy reserves.

This is known as the glucose hypothesis or biophysical theory, according to Dr. Clay Holroyd, a neuroscientist at Ghent University who was not involved in the study.

Instead, it has been proposed by the study’s authors that the brain’s depletion or buildup of specific metabolites may be the cause of mental tiredness.

Cognitive exhaustion may alter brain metabolism, making it more expensive or challenging to exert cognitive control and increasing inclination for actions requiring less cognitive effort. Furthermore, this model predicts that even when a person is mentally exhausted, they may still be able to retain high levels of cognitive control if they are sufficiently motivated.