Fairness Is a Hard-Wired Emotion

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The second option reduced efficiency, but promoted equity. In this option, all the children would be fed, but they'd share fewer meals.

The researchers found that the study participants overwhelmingly chose the second option. This finding echoed other studies that showed that most people are intolerant of inequity, Hsu said.

During the experiment, the volunteers underwent functional magnetic resonance imaging. This allowed the researchers to determine which parts of the brain were most affected during decision-making.

The researchers found that regions of the brain called the insula, putamen and caudate were activated differently, and at different times, during the experiment. The insula responded to changes in equity, while the putamen responded to changes in efficiency. The caudate appeared to blend both equity and efficiency, Hsu said.

The insights involving the insula, which plays a key role in emotions, supports the idea that emotion rather than reason is at the base of people's attitudes about inequality, Hsu said. Also, studies had found that the insula is involved in deciding fairness. But, the putamen and the caudate are activated during reward-related learning, the researchers noted.

"These results support the idea that people care about equity at a very deep level," Hsu said.

Brian Knutson, an assistant professor of psychology and neuroscience at Stanford University, said the findings illustrate just how much emotion is involved in decision-making.

"We are finding that similar brain regions seem to be involved in individual economic well-being and also the well-being of others," he said.

Because the areas of the brain involved in such decisions are located deep inside the brain, it suggests they have a role in evolutionary survival function, Knutson said. "They are serving some sort of survival and emotional function," he said.

Knutson noted that many economic theories assume that people use reason to make decisions, but the areas of the brain involved in equity and efficiency are really areas activated by emotion.

"When people see an unfair offer, they actually have a negative emotional reaction to it," Knutson said. "They have a visceral reaction to unfairness."

More information

To learn more about the human brain, visit the National Institute of Neurological Disorders and Stroke.