Electrophysiological Markers of Fairness and Selfishness Revealed by a Combination of Dictator and Ultimatum Games

Event Related Potentials (ERPs) were recorded from 39 participants who played the role of Allocators in a Dictator Game (DG) and Responders in an Ultimatum Game (UG). Most participants expressed very low levels of altruistic decision making, and two homogeneous groups could be identified, one formed by fair (N = 10) individuals and another by selfish (N = 8) individuals. At fronto-central cortical sites, the ERP early negativity (N1) was reduced in selfish participants with a latency about 10 ms earlier than in fair participants. In fair DG players, the features of the subsequent positive wave P2 suggested that more cognitive resources were required when they allocated the least gains to the other party. P2 latency and amplitude in the selfish group supported the hypothesis that these participants tended to maximize their profit, as expected by a rational Homo economicus. During UG, we observed that a medial frontal negativity (MFN) occurred earlier and with greater amplitude when selfish participants rejected less favorable endowment shares. In this case, all players received zero payoffs, which showed that MFN in selfish participants was associated with a spiteful punishment. At posterior-parietal sites we found that the greater the selfishness, the greater the amplitude of the late positive component (LPC). Our results bring new evidence to the existence of specific somatic markers associated with the activation of distinct cerebral circuits 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.