Irritable after work? That's normal! Here's why 🧐

Do you sometimes feel irritable or find it hard to make decisions after a long day? These sensations are not just a sign of tiredness. They could be rooted in a surprising brain mechanism: the localized exhaustion of certain areas involved in self-control.


Researchers from the IMT School for Advanced Studies Lucca have explored this phenomenon through a unique experiment. They asked 44 volunteers to carry out prolonged and emotionally demanding cognitive tasks while monitoring their brain activity using an electroencephalogram.

These tests revealed unusual brain activity. Participants who had to exert significant control over their emotions showed an increase in delta waves in their prefrontal cortex. These waves, characteristic of sleep, indicate "local drowsiness." This partial sleep specifically affects the brain regions responsible for decision-making and the inhibition of impulsive reactions. In other words, these areas fall asleep without us being aware of it, directly impacting our behavior.

To better understand this impact, researchers then had the same participants engage in cooperative games after the cognitive tasks. The result? Those who had exerted strong emotional control were significantly less cooperative, preferring competitive strategies. The numbers are striking: 86% of “rested” participants chose cooperative behavior, versus only 41% of fatigued participants. These figures illustrate the concrete effect of mental fatigue on our social interactions.

In neuroscience, this phenomenon aligns with the theory of “ego depletion.” Formulated in 1998, this theory posits that human willpower is a finite resource, depletable through prolonged effort. This study provides tangible biological proof. The implications are vast: from economic negotiations to legal agreements, our decisions can be biased by brain exhaustion. A reminder to avoid making important decisions when fatigued.

A practical piece of advice emerges: take the time to “sleep on it” before making any significant decisions. By reactivating our “drowsy” brain regions, we might avoid impulsive and regrettable choices.

What is local sleep and how does it affect our brain?

Local sleep is a neurological phenomenon observed in specific areas of the brain while the rest of it remains awake. This mechanism, identified through sleep research, manifests as delta brain waves, characteristic of deep sleep, appearing only in certain active brain regions.

During prolonged mental fatigue, these delta waves emerge in the frontal cortex, a region involved in decision-making and self-control. This "localized sleep" leads to the partial deactivation of these regions, impairing our ability to regulate behavior and make well-considered decisions.

The consequences are numerous: decreased cooperation, a greater tendency toward aggression, and impulsive choices. These findings reinforce the importance of regular breaks and rest to maintain the efficiency of our essential cognitive functions.