The night changes the brain: Why is it hard to control impulses in the small hours?

Studies from Harvard, Arizona and Pennsylvania universities present the 'brain after midnight' hypothesis, according to which staying awake in the late-night hours changes brain activity and increases impulsivity, negative emotions and the risk of making dangerous decisions. Lack of sleep overloads the brain's synapses and raises dopamine levels, while the frontal area responsible for control weakens. A 2024 study found that the risk of suicide spikes at 3 a.m., and the risk of murder at 2 a.m.

Studies from Harvard, Arizona and Pennsylvania universities coined in 2022 the term 'brain after midnight', describing how staying awake in the late-night hours changes brain activity. According to the hypothesis, the brain becomes more impulsive, more emotional and more prone to negative thoughts, which may lead to actions that will be regretted in daylight. The chemical changes stem from lack of sleep, which overloads the brain's synapses and makes clear thinking difficult, while dopamine levels rise and increase the search for excitement. The frontal area of the brain, responsible for control, is especially vulnerable to lack of sleep. A 2024 study found that the risk of suicide spikes at three in the morning (five times the average) and the risk of murder at two at night (eight times). Another study from 2025 pointed to an increased risk among the Hispanic population. However, not all studies support the hypothesis: a 2024 study showed that prolonged wakefulness actually reduced risk-taking.