PARIS, March 21: A deadly virus has broken out across the planet and you, in your home laboratory, have developed two substances -- one is a vaccine and the other is a fatally toxic liquid, but you don't know which is which.

You have with you two people under your care, and the only way to identify the vaccine is to inject each with one of the substances. Would you kill one of these people in order to save many other lives?

If you feel uncomfortable with this question, that, according to US neurologists, is thanks to a key region of your brain where moral judgments are processed, highlighting the role of emotions in determining right and wrong.

Investigators led by Ralph Adolphs of the California Institute of Technology (Caltech) recruited 30 men and women to answer 50 carefully selected series of hypothetical questions.

The questions fell into three categories -- non-moral choices, for instance about shopping; moral impersonal decisions (of the kind: would you keep money from a wallet you found on the pavement?); and personal moral scenarios, of the kind described above.Six of the volunteers had had damage to the ventromedial prefrontal cortex, or VMPC, a small brain region located just behind the forehead. Twelve had brain damage elsewhere, while the other 12 had no brain damage.

There was no difference among the volunteers in their responses to non-moral and moral impersonal decisions.

But the volunteers with VMPC damage stood out remarkably in the personal moral scenarios.

They plumped swiftly and decisively for “utilitarian” decisions they had no problem with harming or sacrificing one individual for the sake of the common good.

Their counterparts were less likely to do so, and if they did, it was usually after a time was spent pondering the decision.

Normally, humans are blocked from harming each other by aversion, a feeling that co-author Antonio Damasio describes as “rejection of the act, but combined with the social emotion of compassion for that particular person.” Aversion, though, was absent among the people with VMPC lesions.

“Because of their brain damage, they have abnormal social emotions in real life. They lack empathy and compassion,” said Adolphs.

The study, which is being published online tomorrow by the British journal Nature, not only pinpoints the VMPC as critical circuitry for processing intuition and emotion.

It also adds to philosophical debate as to whether humans make moral judgements based on external rules, set by society, or on their own emotions.

Humans, say the authors, may be neurologically unfit for strict utilitarian thinking, because emotion and reason cannot be segregated.

Indeed, they suggest that neuroscience may be able to assess different philosophies to see how compatible these are with human nature.—AFP