January first finds many people making New Year’s resolutions to eat healthier, exercise more, save money, or stop doomscrolling. All these actions can improve well-being in the long-term, but if sticking to your resolutions throughout January leaves your brain feeling like soup, you’re not alone.
Humans have long understood that it’s hard to exert self-control for a prolonged period. However, it is only in recent decades that scientists have been able to peer into the brain and probe the neural mechanisms underlying this phenomenon. These studies have demonstrated that, just like a muscle weakening from over-exertion, parts of the frontal cortex, the brain region responsible for executive functions like attention, planning, problem-solving, self-control, and emotion regulation, become fatigued with use. While it can be easy to get discouraged after a slip up in the pursuit of these new goals, it may be helpful to remember that vulnerability to cognitive fatigue is simply a feature of the human brain, objectively measurable in characteristic patterns of brain activity.
For example, in 2016, researchers at the Pitié-Salpêtrière University Hospital asked one group of participants to perform six hours of tasks requiring executive control, while another group was allowed to read or play video games.1 Over the course of the day, participants exerting self-control in the cognitively demanding activities grew more and more likely to make impulsive choices that provided immediate rewards, while the leisure groups’ impulsivity remained unchanged. Concomitantly, functional magnetic resonance imaging showed decreased activity in the lateral prefrontal cortex in the cognitively fatigued participants.
In a more recent study, researchers found that the frontal cortex not only becomes less active, but may enter a sleep-like state after engaging in tasks requiring self-control.2 “This phenomenon is called local sleep,” explained study coauthor Erica Ordali, a neuroscientist at the University of Florence. “It happens when parts of your brain get tired after they do some task…they start to show brain waves of typical of sleep states, but it happens while we’re still awake.”
Ordali and her colleagues wondered, “What happens to behavior if the local sleep effect occurs in a brain region that is critical for things like decision making, self-control, or [regulating] emotional impulses?”
Researchers subjected participants to 45 minutes of cognitively demanding tasks, measuring their brain activity before and after using high-density electroencephalography. After this period of mentally strenuous activity, brainwaves in the frontal cortex displayed increased delta wave power; these slow-frequency waves are usually indicative of deep sleep. As this executive function region went to “sleep,” so too, it seemed, did participants’ self-control: They acted more impulsively and more aggressively in games that modeled social cooperation and conflict.
Overall, this work shows that exerting self-control is a difficult task for the human brain; the more this resource is used throughout the day, the less there is at the end of the day. So, be patient while developing new habits or breaking old ones. To stave off cognitive fatigue, Ordali recommends rest: “Take more frequent breaks—that’s what helps us restore the state of the brain.”
- Blain B, et al. Neural mechanisms underlying the impact of daylong cognitive work on economic decisions. Proc Natl Acad Sci USA. 2016;113(25):6967-6972
- Ordali E, et al. Prolonged exertion of self-control causes increased sleep-like frontal brain activity and changes in aggressivity and punishment. Proc Natl Acad Sci USA. 2024;121(47):e2404213121
