A study out of the Sackler Institute for Developmental Psychobiology at Cornell published this month in Psychological Science tries to answer the question: at what age do people gain the ability to control themselves in emotionally charged situations?

The study placed 13- to 25-year-olds into a brain scanner while asking them to do a task that required restraint. The instructions were simple: Press a button if you see a bored or scared face, but don’t press it if you see a happy face. The twist was that the subjects performed the task under three conditions: positive arousal, negative arousal and no arousal. In the first condition, they were told ahead of time that at any moment they could be awarded up to $100, while in the second condition they were told there could be a loud noise. In the third condition, the subjects were told nothing.The idea was that the first two conditions would create a sustained period of heightened emotion. It was inspired by the circumstances of criminal behavior: Many crimes by the young are in emotionally or socially charged situations. The question is why, in the heat of the moment, under threat, do they pull the trigger, even when they know better? The results of her experiment involving negative stimulus were striking: 18- to 21-year-olds were less able than 22- to 25-year-olds to restrain themselves from pushing the button when there was the threat of a loud sound. (This diminished cognitive control was not observed under positive or neutral conditions.) In fact, under the threatening condition, the 18- to 21-year olds “weren’t much better than teenagers.” The brain scanners revealed that areas in the prefrontal cortex that regulate emotion showed reduced activity, while areas linked to emotional centers were in high gear.These results support previous brain-imaging studies and postmortem examinations. Brain areas involved in reasoning and self-control, such as the prefrontal cortex, are not fully developed until the mid-20s—a far later age than previously thought. Brain areas involved in emotions such as desire and fear, however, seem to be fully developed by 17. This pattern of brain development creates a perfect storm for crime: Around the ages of 18 to 21, people have the capacity for adult emotions yet a teenager’s ability to control them.