A neural signature of fairness in altruism: a game of theta?

In the dictator game, a proposer can share a certain amount of money between himself or herself and a receiver, who has no opportunity of influencing the offer. Rational choice theory predicts that dictators keep all money for themselves. But people often are offering money to receivers, despite their opportunity to maximize their own profit and therefore showing altruistic behavior. In this study, we investigated the influence of the altruism of the dictator, the anonymity of the decision and the income of the receiver on the offer made by a dictator. Additionally, we were interested in the influence of midfrontal theta activity prior to the offer, indicating the upcoming decision. The height of the offer made by the dictator was dependent on all variables investigated: Altruism of the dictator led to higher offers and income of the receiver led to higher offer the poorer the receivers are. The anonymity of the decision had two effects, depending on the altruism of the dictator, with higher offers for highly altruistic dictators, when they were not observed, and lower offers for less altruistic dictators in this condition. Finally, midfrontal theta activity predicts upcoming fair offers, maybe indicating altruistic motivation or empathy on physiological basis.