There's a reason it feels good to nudge out the kid who cuts in line--it's how we're wired. New research shows that a reward center in the brain zings when people punish cheaters, even if the punishment comes at a cost. The results may shed light on humans' tendency to cooperate.
Humans have a sense of fairness unrivaled in the animal kingdom. Watching some jerk cut off another car on the highway may prompt you to wish the rude driver ill, even if you haven't suffered as a result. To investigate where this sense of fair play may reside in the brain, behavioral economist Ernst Fehr of the University of Zurich, Switzerland, and colleagues scanned the brains of 15 men as they played a game that encouraged cheating.
Two men played at a time. Player A sat in a brain scanner, endowed with some money. The rules required him to give some or all of that money to player B. The amount quadrupled during the transfer to B, and B then had to decide whether to return half or none. When an uncooperative B kept the whole wad, A was given the opportunity to punish B by having the researchers take away some of B's money--any amount A chose.
The researchers found that A levied the biggest fines when the punishment didn't cost A anything. But even when the researchers docked A for half of the amount of the fine, A still told the researchers to take away half of B's stash, on average. The brain scans revealed that while A was deciding on a punishment, his caudate nucleus--a brain region that revs up when people feel satisfaction or pleasure--got busy. When A paid to punish, the caudate nucleus fired more intensely when A settled on a bigger fine. Together, the data suggest that the caudate nucleus anticipates the satisfaction of revenge, and the greater the pleasure the caudate sees coming, the more punishment the players mete out, the team concludes in a paper published 27 August in Science.
Neuroscientist Brian Knutson of Stanford University in California says that the pleasure of punishment may explain why strangers cooperate: In the long run, people are rewarded when they defend standards of fairness. Indeed, he says, the work fits in with other research that shows that the caudate nucleus is active when people anticipate cooperation.