Electrophysiological markers of fairness and selfishness revealed by a combination of Dictator and Ultimatum Games

In the framework of neuroeconomics, Event Related Potentials (ERPs) were recorded during a combination of a Dictator Game (DG), in which the participants always played the role of Allocators, and an Ultimatum Game (UG), in which the participants always played the role of Responders. Behavioral analysis showed that the majority of participants were characterized by very low levels of altruistic decision making, which included two homogenous groups of individuals, one expressing fairness (GrpF, about 26%) and one selfish behavior (GrpS, about 20%). In the analysis of both games, an early negativity (N1) in the fronto-central cortical sites distinguished the GrpF and GrpS participants. The subsequent P2 wave component appeared more associated with the characteristics of the stimulus than with its behavioral value. During UG, we observed that a medial frontal negativity (MFN) occurred earlier and with greater amplitude in GrpS than in GrpF, which depended to a large extent to a spiteful punishment when the Responder refused offers less favorable for himself. The late positive component (LPC) of ERP recorded in posterior-parietal cortical sites was evoked earlier and with greater amplitude during UG than in DG and, in both games, LPC was evoked earlier and with greater amplitude in GrpS than in GrpF. Our results bring new evidence to the existence of different circuits activated by the evaluation of fair and unfair proposals in participants characterized by different expressions of perceived fairness, thus suggesting that particular brain dynamics could be associated with moral decisions.