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Are you more indecisive and irascible than usual after a particularly tiring day at work? Don’t panic, it’s normal. An Italian study, published in the journal PNAS, claims that mental fatigue exhausts certain regions of the brain responsible for self-control and decision-making.
A research team from the IMT School for Advanced Studies in Lucca arrived at this surprising observation after carrying out two experiments intended to test the effect of “ego depletion”, in French). This notion was theorized in 1998 by the American social psychologist Roy Baumeister and his colleagues in a study published in the Journal of Personality and Social Psychology. It is based on the idea that willpower and self-control function as limited resources. Each effort at self-control, such as not letting oneself be overwhelmed by one’s emotions, draws on a “reserve” of will. Once this reserve is depleted, it becomes more difficult to exercise self-control, which could lead to more impulsive or less cooperative behaviors.
To test the veracity of this theory, the researchers asked 44 participants to complete a series of cognitive exercises on a computer for 45 minutes – instead of the 15 minutes usually used in this type of study. In particular, they asked them to watch moving video clips. Half of the volunteers had to keep control of their emotions at all times, while the others could let themselves be free. All participants wore electroencephalogram (EEG) headsets during the experiment, so scientists could monitor their brain activity live.
Analysis of the electroencephalograms revealed that individuals who demonstrated self-control throughout the experiment had increased brain activity in the prefrontal cortex. This region of the brain acts as a sort of control center in the regulation of emotions: it allows us to inhibit impulsive reactions to adopt more thoughtful behavior. But it still needs to work properly.
A state of drowsiness
Indeed, the researchers noticed that volunteers who demonstrated self-control during the experiment showed an increase in delta brain waves in areas of the prefrontal cortex linked to decision-making and impulse control. However, these high amplitude waves are associated with deep sleep in humans, which suggests that these brain areas would have “dozed off” during the experience.
Exercising complete control over one’s emotional reactions for long minutes would therefore plunge the prefrontal cortex into a state of drowsiness. Which can have repercussions on our behavior. The authors of the study had proof of this after conducting another experiment during which they asked the same volunteers to participate in cooperative games. Result: 86% of participants who had not been able to control their emotions during phase 1 of the study showed mutual assistance, compared to only 41% of those who had had to contain themselves. The latter tended to be much more competitive.
In other words, mental fatigue is not something to take lightly. Intense and prolonged intellectual effort affects self-control and decision-making. It is therefore better to avoid making important decisions or discussing potentially conflicting subjects with your loved ones after a long day at work. If you absolutely have to do it, give yourself a break by doing sports or meditation exercises. This will help you be more reasonable.