Justice in the brain: Equity and efficiency are encoded differently

The study was designed to address the psychological and neurological dimensions of two longstanding debates about distributive justice. First, is equity or efficiency more critical to our sense of justice" And second, are such questions solved by reason alone, or does emotion also play a role"

In the experiment, subjects watched an animation on a computer screen. In the animation, a ball traveled from right to left toward a lever that could direct the ball toward one or the other option. Photographs of the affected children represented each option, with numbers for the number of meals that would be lost to those children if that option were selected. By moving the lever, the subjects steered the ball to the option they preferred. At the end of each trial, the subject’s choice was highlighted in red.

In these trails, subjects overwhelmingly chose to preserve equity at the expense of efficiency, Hsu said. “They were all quite inequity averse.” The findings support other studies that show that most people are fairly intolerant of inequity.

The animation, in conjunction with the fMRI, allowed the researchers to view activity in the brain at critical moments in the decision-making process. After analyzing the data, they found that different brain regions – the insula, putamen and caudate – were activated differently, and at different points in the process, Hsu said.

Activation of the insula varied from trial to trial in relation to changes in equity, while activity in the putamen corresponded to changes in efficiency, he said.

In contrast, the caudate appeared to integrate both equity and efficiency once a decision was made.

The involvement of the insula appears to support the notion that emotion plays a role in a person’s attitude towards inequity, Hsu said.

The insula is known to play a key role in the awareness of bodily states and emotions. Studies have shown that it is activated in people experiencing hunger or drug-related cravings, and in those feeling intense emotions such as anger, fear, disgust or happiness. Other research has implicated the insula in mediating fairness.

The putamen and the caudate are activated during reward-related learning.

“You’re seeing the signal in the insula and the putamen initially,” Hsu said. “When they hit the lever you see the insula activation. And when the ball gets to the end you see (activation of) the caudate.”

“The putamen is responding only to the chosen efficiency, which is how many meals get taken away from the kids or how many meals they end up with,” Hsu said. The insula, however, responded to how equitably the burden of lost meals was distributed.

Together, the results “show how the brain encodes two considerations central to the distributive justice calculus and shed light on the cognitivist/sentimentalist debate regarding the psychological underpinnings of distributive justice,” the authors wrote.

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Editor’s note: To reach Ming Hsu, call 217-244-1122; e-mail: .

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