Want to limit aggression? Practice self-control

Criminologists and sociologists have long believed that people commit violent crimes when an opportunity arises and they're low on self-control. "It's an impulsive kind of thing," says Thomas F. Denson, a psychologist at the University of New South Wales. He cowrote the new article with C. Nathan DeWall at the University of Kentucky and Eli J. Finkel at Northwestern University. For the last 10 years or so, psychologists have joined this research, using new ways of manipulating self-control in experiments; they have found that, indeed, self-control and aggression are tightly linked.

A psychological scientist can deplete someone's self-control by telling the subject they're not allowed to take one of the cookies sitting in front of them. Studies have found that, after people have had to control themselves for a while, they behave more aggressively. In a 2009 study, after someone's self-control was depleted, they were more likely to respond aggressively to nasty feedback that ostensibly came from their husband or girlfriend. Specifically, they assigned their partner to hold a painful yoga pose for longer.

On the other hand, it's also possible to practice self-control the same way you would practice the piano. In Denson's experiments, he has people try to use their non-dominant hand for two weeks. So, if they're right-handed, they're told to use their left hand "for pretty much anything that's safe to do," he says. "Using the mouse, stirring your coffee, opening doors. This requires people to practice self-control because their habitual tendency is to use their dominant hands." After two weeks, people who have practiced self-control control their aggression better. In one experiment, they're mildly insulted by another student and have the option of retaliating with a blast of white noise -- but people who have practiced self-control respond less aggressively.

"I think, for me, the most interesting findings that have come out of this is that if you give aggressive people the opportunity to improve their self-control, they're less aggressive," Denson says. It's not that aggressive people don't want to control themselves; they just aren't very good at it. In fact, if you put aggressive people in a brain scanner and monitor their brain activity while insulting them, the parts of the brain involved in self-control are actually more active than in less aggressive people. So it might be possible to teach people who struggle with anger or violence problems to control themselves more easily.

For people who aren't inclined toward violence, it may also be useful to practice self-control -- by trying to improve your posture, for example. In the short term, this can deplete self-control and make it harder to control your impulses. "But if you practice that over the long term, your self-control capacity gets stronger over time," Denson says. "It's just like practicing anything, really -- it's hard at first." But, over time, it can make that annoying colleague easier to deal with.