ORLANDO, FLORIDA--When you're ticked off by reprehensible behavior, a part of the brain called the anterior insula gets huffy, researchers reported here 3 November at the Society for Neuroscience meeting. And the more indignant you are, the more strongly your anterior insula reacts. The finding builds on evidence that particular brain regions are exquisitely sensitive to social interactions.
Helpful, cooperative interactions with other people give the brain a distinctive buzz, cognitive neuroscientists James Rilling and Alan Sanfey of Princeton University and colleagues reported earlier this year. Now they are looking at the dark side of human interactions. One study used a modified version of the “prisoner's dilemma” interaction. People being scanned with functional magnetic resonance imaging (fMRI) had to decide whether to cooperate with a partner and then await their partner's response. If both cooperated, each would win $5. If a subject decided to cooperate but was then betrayed by a partner, the partner would win $6 and the subject would get nothing. In response to such selfish behavior, the subject's anterior insula was extremely active.
In a second study, called the "ultimatum game," the subject's partner was given $10 and told to propose a way to divvy up the money. People could either accept the proposed split and both would keep their share of the money, or reject it and nobody would earn anything. People who were offered the short end of a $7 and $3 split, $8 and $2 split, or a $9 and $1 split had more anterior insula activity than those offered an even split, and the anterior insula lit up most in people offered the worst splits. "We think this is a neural correlate of indignation," says Rilling, who points out that studies of disgust have also found activity in the anterior insula.
The researchers are addressing "a very interesting issue," says Marcus Raichle of Washington University in St. Louis, Missouri. Indignation even prompted some surprising behavior: "Despite the logical response that you should take whatever you can get [in the ultimatum game], people behave in a counterintuitive way"--punishing their partner even at the price of denying themselves money. The new research suggests that such spiteful self-sacrifice might originate in the anterior insula.