After a long day of work where brain tasks are linked, we can sometimes feel drained of all energy. As written Diana Kwon in the journal Scientific American, in such times, “you probably want to relax in front of a series rather than check off another box on your to-do list”. The findings of a new study shed light on the biological reasons for this phenomenon.
This is a question that scientists have already tried to answer. In the 2000s, a study set out to demonstrate that long periods of concentration could lead to reduced blood glucose levels, so consuming a sugary drink was thought to help kick-start brain boost. But according to Anthony Wiehlerresearcher in cognitive neuroscience at Pitié-Salpêtrière, “if we look at all the studies as a whole, there is no proven link”. Indeed, other studies did not achieve the same results.
Then in 2016, says the journalist, a study carried out at Pitié-Salpêtrière and led by Mathias Pessiglione, demonstrated that long periods of intense mental activity encourage study participants to choose an immediate reward (a smaller amount of money now rather than more later). This is accompanied by a decline in brain activity in the prefrontal cortex: area of the brain involved in decision making.
To understand this phenomenon a little better, Pitié’s team of researchers has once again looked into this question. Forty people were herded into a lab and tasked with performing repetitive but mentally intense tasks for just over six hours. The participants were divided into two groups, one of which had even more difficult tasks to complete. At the end of the day, members of both groups reported similar levels of fatigue, but those assigned the more complex tasks were more likely to choose to go home with an immediate reward—as in the previous study.
To understand this choice, the scientists measured the participants’ levels of neurotransmitters. Those who had to perform the most complex tasks had higher levels of concentration and release of the neurotransmitter glutamate in the prefrontal cortex. Clearly, more than a decline in resources, fatigue is rather due to an accumulation of chemicals in the brain, like a kind of overload.
According to the researcher Matthew Apps, a neuroscientist at the University of Birmingham, who was not involved in the study, the results of this study could lead to other discoveries. The accumulation of glutamate could partly explain the fatigue felt by people suffering from burnout, we could also look into a technique to avoid this accumulation and therefore the fatigue that accompanies it.
Of course, the study also leaves several questions unanswered that could be the subject of further research: How do you get rid of this buildup? How do other parts of the brain react? What are the other factors responsible for fatigue?