Feeling right from wrong: brain's social emotions steer moral judgments.

People who suffer damage to a brain area that generates compassion, shame, and other social sentiments apply coldly rational thinking to hypothetical moral dilemmas, even those that involve terrible personal loss, a team of neuroscientists finds.

In contrast, people with healthy brains or with damage to other neural regions usually permit their personal concerns to override rational responses to such moral quandaries, say Michael Koenigs of the National Institute of Neurological Disorders and Stroke in Bethesda, Md., and his coworkers.

The new findings, published online and slated to appear in Nature, support the idea that emotional, intuitive reactions orchestrate moral judgments of people with intact brains.

"Human beings can judge [moral dilemmas] on the basis of reason alone, of emotion alone, or of a mixture; says study coauthor Antonio Damasio of the University of Southern California in Los Angeles. "Life is too complicated for it to be any simpler than that."

Koenigs' team studied six people with damage limited to the ventromedial prefrontal cortex, a brain region previously implicated in social emotions.

The researchers compared patients' responses to 50 hypothetical nonmoral and moral dilemmas with the responses of 12 adults who had no brain damage and of 12 people with brain damage that didn't affect the emotional structures.

In one nonmoral scenario, volunteers were asked to imagine that they were farmworkers running a turnip-harvesting machine. They decided whether to take the machine down one path to harvest 20 bushels or down another to harvest 10 bushels.

The moral dilemmas included impersonal and personal situations. In an impersonal case, participants imagined that they were driving a runaway trolley approaching a fork in the tracks. They decided whether or not to direct the trolley toward a single worker on one track to avoid killing five workers on the other track.

In a personal scenario, volunteers were asked whether they, as civilians hiding with comrades in a war zone, would smother their own crying babies to avoid detection by enemy soldiers ordered to kill civilians.

In about two-thirds of the responses to the nonmoral and impersonal situations, members of all three groups endorsed the greater good, such as killing one worker to spare five others.

A disparity emerged on personal judgments, however. In half of the responses, people with prefrontal damage advocated behavior for the greater good at their own expense, such as smothering one's crying baby to keep enemy soldiers away. Within the other two groups, only one-quarter of responses reflected that pattern.

The researchers propose that prefrontal damage dilutes emotional reactions to harm that one inflicts on others. People with such damage thus solve moral dilemmas by following social conventions for helping as many folks as possible and hurting as few as possible, rather than by considering personal feelings.

"This study vividly illustrates the way that emotions animate or color moral judgments in healthy people, remarks psychologist Jonathan Haidt of the University of Virginia in Charlottesville. "In real life, the loss of social emotions is disastrous for moral judgment and action."