🧨 Why Mental Exhaustion Makes You Antisocial

New research reveals how mental fatigue impacts brain function and escalates impulsive aggression

Our daily behaviors are affected by all kinds of internal and external influences. We like to think of ourselves as having good self-control, but this has its limits. It often only takes a moment of hunger or frustration to turn what would normally be a friendly smile into an aggressive snap.

The idea that self-control is a limited and depletable resource has been controversial in the last few years, with studies producing inconsistent results. But research continues to find that our capacity for self-control can be drained by certain types of exhaustive mental effort. The nuances around what types of activity most deplete self-control and how this depletion actually impacts our behavior are less certain.

One new study has looked into self-control depletion in the context of aggressive behavior. It examines how fatigue affects brain function, and how those changes in brain function impact our social choices. The findings provide an interesting new perspective on the real-life risks of allowing ourselves to get mentally exhausted.

🧪 What did the researchers do?

In a 2024 study published in PNAS, researchers recruited 44 participants and split them into two groups, with each group completing a set of cognitive tasks:

• No fatigue group: this group completed a set of relatively easy cognitive tasks without burdening their self-control

• Frontal fatigue group: this group completed a similar set of cognitive tasks but with a high, exhausting demand on self-control

The “frontal” in “frontal fatigue” refers to the brain areas that are most impacted by cognitive tasks involving self-control and decision-making. The researchers wanted to look for signs of mental exhaustion in frontal areas of the brain after prolonged effort with tasks that place a high burden on these functions.

To collect brain activity data, the researchers used EEG recording before and after participants completed their assigned tasks. Each participant spent a total of 45 minutes on their cognitive tasks before also completing another set of economic games. These games were designed to test each person’s willingness to be cooperative and unselfish during social interactions.

One example economic game was the “Hawk and Dove Game” in which participants were placed in pairs, and each of them could choose between an aggressive interaction or peaceful interaction with the other player. If one person attacks while the other is peaceful, that attacker takes most of the points on offer. If both players are peaceful, they share the points equally. If both players attack, neither player wins any points.

🔍 What did the research find?

The researchers first checked whether the demanding cognitive tasks really did exhaust people’s frontal brain areas. The EEG data showed that compared to participants in the “no fatigue” group, participants in the “frontal fatigue” group had a significant increase in sleep-like delta brainwave activity in their frontal cortex after completing their tasks. So engaging in tasks designed to deplete self-control produced the expected signals of fatigue in frontal brain areas.

But how did this change in the brain affect real behavior? In the Hawk and Dove Game, participants in the “frontal fatigue” group only selected the peaceful strategy 41% of the time compared to 86% for the “no fatigue” group. In other words, after having their mental energy drained by demanding cognitive tasks, people were more likely to behave aggressively when given the option.

The researchers replicated this effect in the Hawk and Dove Game on a second larger sample of 403 participants, suggesting it’s a robust finding. Several other economic games didn’t show the same behavioral changes though, so it’s likely that frontal fatigue affects some of our behavioral or social faculties more than others.

Mental exhaustion can often feel like a general decline in energy and motivation, but based on these results, the effects can be specific in quite surprising ways. In some cases, rather than dropping motivation overall, exhaustion may boost your chances of behaving aggressively and hinder your ability to find cooperative solutions to social challenges.

⭐️ Takeaway tips

#1. Be aware of the social risks of mental exhaustion

• Based on the results above, one major behavioral risk of mental fatigue is associated with social interactions. When you want to be prosocial and cooperative, make sure you’re feeling rested and try not to over-exert yourself on demanding cognitive tasks that are likely to exhaust your self-control capacity. If you find yourself in a challenging social scenario, be aware of how your current cognitive state may bias your decisions one way or another.

#2. Mix up task types through your day

• Throughout your day, try to organize your tasks so they’re not repeatedly draining you in the same way. If you spend your entire morning on tasks that require a lot of careful decision-making and self-control, you may impair your ability to use those skills when urgently needed at some point in the afternoon. Instead, try to schedule your daily tasks according to both their priority level AND their likely cognitive demands.

#3. Take frequent breaks

• The most obvious tip of all is to take work breaks seriously and avoid driving right over them every time another idea or priority appears on your task list. There’s always something we could be doing, and productivity feels like it stalls every time we pause. But in reality, breaks help to keep you functioning optimally through the day and limit skill fatigue. You won’t always notice the bad decisions you’ve made as a result of moments of exhaustion.

“Beware of no man more than of yourself; we carry our worst enemies within us.”

~ Charles Spurgeon

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