Hard physical work, sports and physical exercise are sure to cause fatigue. But mental work also wears out. French researchers have studied why it can be stressful to focus for hours. Their results are published in the scientific journal current biologyIt turns out that fatigue has very specific biological causes.
In the study, participants were divided into two groups, and asked to focus for six hours, with two short periods of ten minutes each. Participants in one group were shown letters every second and had to decide whether they had seen the same letter as three paintings earlier. This was the most demanding job. The second group had almost the same task: they had to determine if the letter presented to them was the same letter they had just seen before.
“After six hours, regardless of the difficulty of the task, both groups reported feeling fatigued,” says Antonius Wheeler, lead author of the study and a behavioral scientist at the Institute of the Brain and Spine (ICM) at Pitié-Salpêtrière Hospital in Paris. . This may also be due to the fact that we feel exhausted after a day’s work, says Wiehler.
But since “custom” doesn’t actually serve as a scientific argument, researchers have continued to search for a biological explanation for mental fatigue. Previous studies had already determined that the lateral prefrontal cortex plays a greater role in thought processes, planning or decision-making, but they haven’t found out exactly why.
With the help of magnetic resonance spectroscopy (MRS), the team of scientists investigated the matter. “We found out it had to do with the amino acid glutamate,” Wehler explains. “In the groups that had to solve the most difficult tasks, the glutamate concentration increased over time.” This, together with the above findings, supports the hypothesis that glutamate accumulation impairs prefrontal cortex activation. Concentrating becomes more difficult.
20 euros or 50 euros?
Some may now ask “So what?”. After all, we are already accustomed to the limits of our cognitive performance. But the study also shows that increased levels of glutamate affect our decisions and therefore our daily lives.
“We ask the participants to make simple economic decisions: would they prefer 20 euros now or 50 euros a year?” The result: Participants in the group with more cognitively challenging tasks tended to prefer quick money, while the other group thought long-term. “When cognitive fatigue sets in, we choose simpler processes or procedures that don’t require effort or waiting,” Wehler explains. So it makes sense to make important decisions at the beginning of the day, not after a busy day.
Are there cognitive limits?
But is there any way to restore or train our cognitive performance? “Good question, as yet we don’t know how to prevent glutamate release, or whether that is advisable,” Wehler says.
It is not clear if cognitive flexibility can be trained. “Very likely,” Wehler says. “However, we still don’t know if and how this affects decisions. Probably not.” (ie/ms)