Study Finds Brain Injury Changes Moral JudgmentBy BENEDICT CAREY
March 21, 2007
Damage to an area of the brain behind the forehead, inches behind the eyes, transforms the way people make moral judgments in life-or-death situations, scientists are reporting today. In a new study, people with this rare injury expressed increased willingness to kill or harm another person if doing so would save others' lives.
The findings are the most direct evidence to date that humans’ native revulsion for hurting others relies on a part of neural anatomy, one that likely evolved before the brain regions responsible for analysis and planning.
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, published online by the journal Nature, confirm the central role of the damaged region — the ventromedial prefrontal cortex, which is thought to generate 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, and experts say that any evidence of damage to this ventromedial area could sway judgments of moral competency in some cases.
The new study focused on six patients who had suffered very specific 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. The term ventral means underneath, and medial means near the middle. The area in adults is about the size of a child’s fist.
People with this injury can be lucid, easygoing, talkative and intelligent, but blind to subtle social cues, making them socially awkward. They also have some of the same moral instincts that others do.
The researchers, from the University of Iowa and other institutions, had them respond to several moral challenges. In one, they had to decide whether to divert a runaway boxcar that was about to kill a group of five workmen. To save they workers they would have to flip a switch, sending the car hurtling into another man, who would be killed.
They strongly favored flipping the switch, just as group of people without injuries did. A third group, with brain damage that did not affect the ventromedial cortex, made the same decision.
All three groups also strongly rejected doing harm to others in situations that were not a matter of trading one certain death for another. They would not send a daughter to work in the pornography industry to fend off crushing poverty, or kill an infant they felt they could not care for.
But a large difference in the participants’ decisions emerged when there was no switch to flip — when they had to choose between taking direct action to kill or harm someone (pushing him in front of the runaway boxcar, for example) and serving a greater good.
Those with ventromedial injuries were about twice as likely as the other participants to say they would push someone in front of the train (if that was the only option), or to poison someone with AIDS who was bent on infecting others, or suffocate a baby whose crying would reveal to enemy soldiers where the subject and family and friends were hiding.
“The difference was very clear, for all of the ventromedial patients,” said Dr. Michael Koenigs, a neuroscientist at the National Institutes of Health who led the study while at the University of Iowa. After repeatedly endorsing killing in these high-conflict situations, he added, one patient told him, “Jeez, I’ve turned into a killer.”
The other authors were Dr. Daniel Tranel of Iowa and neuroscientists from Harvard, the University of Southern California and the California Institute of Technology.
The ventromedial area is a primitive part of the cortex that appears to have evolved to help humans and other mammals navigate social interactions. The area has connections to deeper, unconscious regions like the brain stem, which transmit physical sensations of attraction or discomfort; and the amygdala, a gumdrop of neural tissue that registers threats, social and otherwise. The ventromedial area integrates these signals with others from the cortex, including emotional memories, to help generate familiar social reactions.
“This area when it’s working will give rise to social emotions that we can feel, like embarrassment, guilt, compassion that are critical to guiding our social behavior,” said Dr. Antonio Damasio, a co-author and a neuroscientist at the Brain and Creativity Institute at U.S.C. These sensations in effect put a finger on the brain’s conscious, cost-benefit scale weighing moral dilemmas, Dr. Damasio argues, creating a tension that even trained snipers can feel when having to pull the trigger on an enemy.
This tension between cost-benefit calculations and instinctive emotion in part reflects the brain’s continuing adjustment to the vast social changes that have occurred since the ventromedial area first took shape. The ventromedial area most likely adapted to assist the brain in making snap moral decisions in small kin groups— to spare a valuable group member’s life after a fight, for instance. As human communities became larger and increasingly complex, so did the cortical structures involved in parsing ethical dilemmas. But the more primitive ventromedial area continued to anchor it with emotional insistence an ancient principle: respect for the life of another human being.
“A nice way to think about it,” Dr. Damasio said, “is that we have this emotional system built in, and over the years culture has worked on it to make it even better.”