THURSDAY, May 8, 2008 (HealthDay News) -- The belief that things should be divided fairly among members of a group isn't just a matter of culture or reason -- it's an emotion that's built into the human brain.
That's the suggestion of a new study that posed the question: Is it better to give food to some hungry children while others go hungry? Or is it better that every child get a share, albeit a smaller one?
"People prefer equity, when all things are equal, to efficiency," said study lead researcher Ming Hsu, a fellow at the University of Illinois Beckman Institute for Advanced Science and Technology.
And different regions of the brain are involved when making decisions involving fairness or efficiency, he said.
"In terms of the brain, we find areas of the insular cortex are activated when people were choosing the equitable allocation of food," Hsu said. "Given the involvement of the insular cortex in emotions and fairness judgments, we conclude that emotions are underlying equity judgments."
Other areas of the brain are activated when people are making judgments about efficiency, he said.
But, not everyone is sensitive to equity, Hsu noted. "Some people care less about equity, and that's associated with a lower sensitivity in their insula," he said. "When these people are confronted with inequitable situations, their insula is activated less."
The study, by researchers at the University of Illinois and the California Institute of Technology, was published in the May 8 issue of Science.
For the study, the volunteers were hypothetically asked to distribute food to children in an orphanage in Uganda. The children would be given the cash equivalent of 24 meals, a "gift" from the research team to the orphanage.
But, a number of meals would have to be cut for some of the children. So, the volunteers were given two options to deal with the problem.
In one option, 15 meals could be taken from one child, or 13 from another child, or five from yet another child, for instance. Choosing this option, the total number of meals lost would be less, but one child would suffer from all cuts. Efficiency would be maintained at the expense of equity.
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."
To learn more about the human brain, visit the National Institute of Neurological Disorders and Stroke.