Do you find yourself feeling more indecisive and irritable than usual after a hard day’s work? Rest assured, it’s normal: an Italian study published in the journal PNAS reveals that mental fatigue depletes certain brain regions responsible for self-control and decision-making.
Researchers at the ITM School for Advanced Studies in Lucca confirmed this after conducting two experiments designed to test the effect of “ego depletion”. This concept was theorised 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. All the effort required to maintain self-control, such as not allowing yourself to be overwhelmed by your emotions, draws on a finite “reserve” of willpower.
Once this reserve is depleted, it becomes more difficult to exercise self-control, which could lead to more impulsive or less cooperative behaviour.
To put this theory to the test, the researchers asked 44 participants to perform 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 were asked to keep control of their emotions at all times, while the others were given free rein.
All participants wore electroencephalogram (EEG) headsets during the experiment, so that the scientists could follow their brain activity.
Analysis of the EEGs revealed that individuals who demonstrated self-control throughout the experiment showed increased brain activity in the prefrontal cortex. This region of the brain acts as a kind of control centre for emotion regulation, inhibiting impulsive reactions in favour of more measured behaviour. But to do so, it has to be functioning properly.
Indeed, the researchers noted that volunteers who demonstrated self-control during the experiment showed an increase in delta brain waves in areas of the prefrontal cortex associated with decision-making and impulse control. These high-amplitude waves are associated with deep sleep in humans, suggesting that these brain areas may have become “sleepy” or fatigued during the experiment.
Exercising complete control over our emotional reactions for extended periods of time could, therefore, plunge the prefrontal cortex into a state of somnolence, marked by the emergence of sleep-like brain activity. And this can have repercussions on our behaviour.
The experts found evidence of this after conducting another experiment in which they asked the same volunteers to take part in cooperative games. They found that 86% of participants who had not been in control of their emotions during phase one of the study were helpful, compared with only 41% of those who had to restrain themselves. The latter tended to be much more competitive.
So, it appears mental fatigue is not something to be taken lightly; intense and prolonged mental effort can affect our self-control and decision-making. As such, it’s best to avoid making important decisions or discussing potentially conflictual subjects with your loved ones after a hard day’s work.
If there’s no way around it, then giving yourself a break by taking some exercise or practising meditation could help you act more reasonably.