Mental exhaustion makes people become mean, ‘hostile’: Study

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Some people who appear to be having a bad day might simply be mentally exhausted.

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A new study has found that prolonged mental fatigue or exertion leads to changes in the brain’s frontal cortex, which heightens aggressive or impulsive behaviour.

The research suggests that mental exhaustion causes brain activity similar to sleep when it comes to making decisions, which can cause increased aggression and reduced cooperation in social interactions.

In the study, published Monday in the journal PNAS, researchers at the IMT School of Advanced Studies Lucca explore the theory of “ego depletion” — the idea that willpower diminishes with use — and how it is linked to physical changes in brain areas that manage tasks such as decision-making or resisting temptations.

More specifically, when mental fatigue strikes in an awake brain, it depletes that reserve that leads to less willpower and making more bad choices.

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Participants underwent a series of tasks For this study, scientists from the IMT School for Advanced Studies Lucca in Italy wanted to see how “ego depletion” affects brain activity.

They had participants were subjected to an hour-long series of tasks designed to wear them out mentally, before playing games that required varying degrees of aggression and cooperation.

One of the games was the “hawk and dove” game where limited resources are to be shared in a hostile environment situation, with people having the choice between collaborating or overbearing behaviour, which may result in the loss of resources for both parties.

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Researchers measured the electrical activity in their brains as they played the games and determined the participants who were subjected to cognitive fatigue were significantly more uncooperative and hostile compared to a control group.

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The peaceful cooperation rate dropped from 86% to 41% in the “No Fatigue” group.

“Our study shows that mental fatigue has a measurable effect on behavior and that, when a certain degree of fatigue sets in, people are more likely to behave in a hostile manner,” Erica Ordali, a research fellow at the IMT School and first author of the paper, said.

Ordali’s team found that spending just 45 minutes on executive function tasks like making plans and solving problems increases the likelihood an individual will show aggression in social situations.

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They linked the behavioural changes to sleep-like activity within frontal brain areas related to decision-making and impulse control.

The disengagement of these areas explains the reduced ability to self-control, according to Pietro Pietrini, co-author of the paper and director of the Molecular Mind Lab at the IMT School.

“Overall, these findings have important implications for multiple situations in everyday life, including economic transactions and legal agreements, as they demonstrate that when the brain is ‘tired’ we may make choices that go even opposite to our own interest.”

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