MORALITY is not based on social conscience or religion, but a brain region just above and behind the right ear, research suggests.
Scientists found they were able to alter people's moral judgments by directing magnetic pulses at a knot of nerve cells known as the right temporo-parietal junction (RTPJ).
Volunteers subjected to a number of "moral maze" tests had their notions of right and wrong disrupted. In one scenario, participants were asked how permissible it was for a man to let his girlfriend walk across a bridge he knew was unsafe.
After receiving a 500 millisecond magnetic pulse to the scalp, the volunteers delivered verdicts based on outcome rather than moral principle. If the girlfriend made it across the bridge safely, her boyfriend was not seen as having done anything wrong.
Lead researcher Dr Liane Young, from the Massachusetts Institute of Technology (MIT) said: "You think of morality as being a really high-level behaviour. To be able to apply a magnetic field to a specific brain region and change people's moral judgments is really astonishing."
Previous studies had shown the RTPJ to be highly active when people thought about the intentions, thoughts and beliefs of others. The MIT team reasoned that since judging the morality of an action depended on assessing beliefs and intentions, it might involve the RTPJ. The region is situated at the brain's surface above and behind the right ear.
To investigate the hypothesis, the scientists first pinpointed the RTPJ in each of up to 12 volunteers using a brain scan.
Experiments were then carried out in which participants were subjected to magnetic pulses targeted at the RTPJ. The non-invasive technique, known as transcranial magnetic stimulation (TMS), creates weak electric currents that temporarily block the ability of brain cells to fire normally.
In one test, volunteers were exposed to TMS for 25 minutes before reading a series of 192 stories involving morally questionable characters. Participants were asked to make moral judgments of the characters' actions on a scale of one (absolutely forbidden) to seven (absolutely permissible).
A second experiment involved applying a 500-millisecond TMS burst at the moment a volunteer was asked to make a moral judgment.
In both cases, the researchers found that when the RTPJ was disrupted, volunteers were more likely to judge actions solely on the basis of whether they caused harm or not. Irresponsible or deliberate actions that might have resulted in harm were seen as morally acceptable if the story had a "happy ending".
Writing in the journal Proceedings of the National Academy of Sciences, the researchers said: "A particularly striking effect occurred for attempted harms (eg 'actors' who intended but failed to do harm) … TMS to the RTPJ caused participants to judge attempted harms as less morally forbidden and more morally permissible.
"Thus, interfering with activity in the RTPJ disrupts the capacity to use mental states in moral judgment, especially in the case of attempted harms."