The researchers emphasize that the study was small and that the moral decisions were hypothetical; the results cannot predict how people with or without brain injuries will act in real life-or-death situations. Yet the findings, appearing in the journal Nature, confirm the central role of the damaged region, the ventromedial prefrontal cortex, which is thought to give rise to social emotions, like compassion.

Previous studies showed that this region was active during moral decision making, and that damage to it and neighboring areas from severe dementia affected moral judgments. The new study seals the case by demonstrating that a very specific kind of emotion-based judgment is altered when the region is offline. In extreme circumstances, people with the injury will even endorse suffocating an infant if that would save more lives.

“I think it’s very convincing now that there are at least two systems working when we make moral judgments,” said Joshua Greene, a psychologist at Harvard who was not involved in the study. “There’s an emotional system that depends on this specific part of the brain, and another system that performs more utilitarian cost-benefit analyses which in these people is clearly intact.”

The finding could have implications for legal cases. Jurors have reduced sentences based on brain-imaging results showing damage. The new study focused on six patients who had suffered damage to the ventromedial area from an aneurysm or a tumor. The cortex is the thick outer wrapping of the brain, where the distinctly human, mostly conscious functions of thinking and language reside. “Ventral” means “underneath”, and “medial” means “near the middle.” The area in adults is about the size of a large plum.

Abridged from: The New York Times; March 22, 2007.