Six patients with damage to their ventral medial prefrontal cortex (VMPC), an area involved in emotions, were recruited. The patients, who have normal IQ and knowledge of social and moral norms, were presented with: impersonal moral choices (Do you divert a runaway trolley off its track, saving the lives of five workmen but imperilling a single workman on the other track?); personal moral choices (Do you kill a fellow hostage in order that you and eight children can escape from terrorists?); and non-moral decisions (Do you buy a branded product or buy a supermarket's own version?).
The choices made by the patients with prefrontal cortex damage were compared with those made by healthy controls and by patients with damage to parts of the brain not associated with emotion.
The groups didn't differ in how they made impersonal moral choices and non-moral decisions. Crucially, however, the patients with prefrontal cortex damage tended to answer more ruthlessly than the other participants when it came to 13 out of 21 personal moral decisions. These decisions tended to pit the welfare of the majority against the participant having to commit deliberate harm to others. Repulsion at committing such deliberate harm caused the control participants to sacrifice the well-being of the majority, whereas the patients with prefrontal cortex damage tended to make more 'utilitarian', logical choices, harming one person to save the many.
“What is absolutely astonishing about our results is how selective the deficit is” said co-author Marc Hauser. “Damage to the frontal lobe leaves intact a suite of moral problem solving abilities, but damages judgements in which an aversive action is put into direct conflict with a strong utilitarian outcome”.
Koenigs, M., Young, L., Adolphs, R., Tranel, D., Cushman, F., Hauser, M. & Damasio, A. (2007). Damage to the prefrontal cortex increases utilitarian moral judgements. Nature.
Link to full list of the moral decisions (pdf).
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