Revenge is indeed sweet, study finds
August 26, 2004
Lauran Neergaard / Associated Press



WASHINGTON, Aug 26 (Associated Press) - Dirty Harry had it right: Brain scans show revenge really might make your day. Planning revenge sparks enough satisfaction to motivate getting even - and the amount of satisfaction actually predicts who will go to greater lengths to do so, report Swiss researchers who monitored people's brain activity during an elaborate game of double-cross.

That may not sound too surprising. Just consider the old saying, "Revenge is sweet."

But beyond helping to unravel how the brain makes social and moral decisions, the study illustrates growing interest in the interaction between emotion and cognition - which in turn influences other fields such as how to better model the economy.

The new study chips "yet another sliver from the rational model of economic man," said Stanford University psychologist Brian Knutson, who reviewed the Swiss research. "Instead of cold, calculated reason, it is passion that may plant the seeds of revenge," he said.

People often are eager to punish wrongdoers even if the revenge brings them no personal gain or actually costs them something. From a practical standpoint, that may seem irrational.

In research reported in Friday's edition of the journal Science, University of Zurich scientists used PET scans to monitor the brain activity of game players to determine what motivates that type of revenge.

Two players could either trust and cooperate with each other so they both earned money. Or one could double-cross the other and keep an unfair share. Sometimes the double-cross was deliberate; other times, rules of the game dictated it. The victim could retaliate by fining the double-crosser different amounts, but sometimes had to spend his own money to impose that fine.

All 14 players chose revenge whenever the double-cross was deliberate and the retaliation free. Only three retaliated when the double-cross wasn't deliberate. Twelve of 14 players punished a deliberate double-cross even if it cost them additional money.

The PET scans showed a brain region known to be important for enjoyment and satisfaction - the dorsal striatum - became active in those players who decided to retaliate. It wasn't an afterglow from revenge, but satisfaction from anticipating it.

When the retaliation cost them money, a second brain region that helps weigh costs and benefits got involved, too, but the striatum remained key. The level of activity actually predicted which players would spend more money to get revenge.

"Their behavior does not reflect blind revenge that follows from overwhelming emotions," cautioned study co-author Ernst Fehr, director of the University of Zurich's economic research institute. "They reduce punishment if it is costly for them in the same way as they reduce buying goods if the goods become more expensive."

Moreover, that same satisfaction-causing brain circuitry seems to be involved in the evolution of human cooperation, providing incentive to get along with strangers in setting social norms, the researchers write in Science. Punishing violators of those norms even if you personally don't stand to gain may be the flip side.

The study involved only men, and more work is needed to see if women and people of varying social and income groups react similarly, Stanford's Knutson said.

But the research is important as scientists try to dissect how emotion interacts with analytical decision-making, he stressed.

"For a long time, sociologists and economists have not paid a lot of attention to people's feelings, especially before an event," Knutson explained. "It's almost like your mind imagines the outcome before it happens. That's a lot of what motivates behavior."