Brain Split on Moral Choices
March 22nd 2007 07:01
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Less than a decade ago, most psychologists and neurobiologists assumed there was one moral center of the brain that churned out the judgments by which people lived their lives.
But in research published Wednesday in the journal Nature, a team of scientists presented strong evidence that moral decisions are the result of at least two competing processes - one emotionally driven and one more rational.
The results could help researchers understand why people make the decisions they do, and perhaps shed light on the roots of criminal behavior, said one of the study's co-authors, Fiery Cushman, a psychologist at Harvard University.
Cushman and his colleagues, who included Caltech neuroscientist Ralph Adolphs, reached their conclusions by comparing normal subjects to those with damage to a front area of the brain called the ventromedial prefrontal cortex, which is involved in emotion.
To each group, they posed moral dilemmas in which an emotionally difficult sacrifice was needed to protect the greater good.
In one example, Cushman said, they were told of a hypothetical scenario in which a family was hiding from an enemy army that approached just as the youngest child stepped
on a nail. If the child cried out, the entire family would be revealed and killed; the only other option would be to smother him.
"The question is, would you sacrifice one child for the good of the family?" Cushman said.
On average, 50 percent of normal subjects were not able to make the quick choice to sacrifice the child. For the six study subjects with damaged emotional regions in their brain, 80percent could make such a decision.
"By removing the capacity to have that kind of kneejerk `Ah! Don't kill the baby!' response, you're allowing them to express more of that rational response," Cushman said.
"This shows that in a sense, morality is accomplished by a competition between these two systems, and that in these guys, in effect, one of the competitors has been knocked out," he said.
The work builds on other recent brain imaging and psychological studies into the source of morality.
In 2001, Harvard neuroscientist Joshua Green lead an imaging study that showed that a morally challenging dilemma - whether to push a large man in front of a train to stop it from hitting five others - caused more activity in the emotional side of the brain than a less difficult quandary.
A separate study at Northwestern University later showed that manipulating subjects' emotions by having them watch a funny "Saturday Night Live" skit made them more likely to make the utilitarian moral judgment that would protect the greater good.
But these latest results, said Green, who was not involved in the study, are "the most compelling demonstration yet."
elise.kleeman@sgvn.com Full acknowledgement is give to the author
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