Joshua Greene asked participants how they would respond in two situations. In the first, they are watching five people in a trolley rolling down a railway track towards a cliff edge. They can save the five by throwing the lever of a set of points to divert the trolley—but doing so will kill a person standing on this second track. Although one life will be sacrificed, five will be saved, and most people say they would throw the lever. In the second scenario, the individuals imagine themselves standing next to an exceptionally fat man on a footbridge over the track. This time they can stop the runaway trolley by pushing their companion on to the track in front of it. Here too, one man will die, but five will be saved. In this case, however, most people say they would not take action.
What is the philosophical difference?  Maybe none – but by putting the two situations to his participants while they underwent functional MRI, Greene showed that contemplating the footbridge dilemma prompted more activity in areas of the brain associated with emotion than did the points scenario.

Greene's findings challenge the view that moral judgments must be based entirely on reason. Indeed, he believes that emotion is a legitimate and inescapable part of moral decision-making.

Macbeth effect described by Canadian researchers whereby act of washing hands after being asked to describe an unethical act changes individuals' propensity to offer voluntary help.  

From the Lancet.