"We often consider dilemmas that have to do with fairness to be moral dilemmas. A fascinating, well-known finding involves what is known as the ultimatum game. Two people are involved in this game and they are only allowed one round. One person is given twenty dollars, and he has to split it with the other player, but he determines the percent split. Both players get to keep whatever amount of money is first offered. However, if the player who is offered the money refuses the offer, then neither gets any.
"In a rational world, the player who gets offered the money should take any offer because that is the only way he will come out ahead. That, however, is not how people react. They will accept the money only if they think it is a fair offer, ranging from at least six to eight dollars. Ernst Fehr and his colleagues used transcranial electric stimulation to disrupt brain functioning in the prefrontal cortex and found that when the function of the right dorsolateral prefrontal cortex was disrupted, people would accept lower offers while still judging them to be unfair.
"Since suppression of this area increased selfish responses to unfair offers, it suggests that this area normally inhibits self-interest (taking any offer) and reduces the impact of the selfish urges on the decision-making processes, and thus plays a key role in implementing behaviors that are fair. More evidence for this region’s inhibiting selfish responses is from Damasio’s group, which has given moral tests to adults who have had injuries to this area since childhood. Their answers were excessively egocentric, as was their behavior. They exhibited a lack of self-centered inhibition and did not take another’s perspective. people who acquire these types of lesions as adults, such as the patients Damasio tested with the moral dilemma problems, can compensate better, which suggests the neural systems that had been impaired at an early age were critical for the acquisition of social knowledge. Many examples of moral circuits have been identified, and they seem to be distributed all over the brain…"
--Michael S. Gazzaniga, Who's in Charge?: Free Will and the Science of the Brain