An electrophysiological index of outcome evaluation that may influence subsequent cooperation and aggression strategies.

Human social decision-making is significantly modulated by previous decision outcomes. Using event-related potentials (ERPs), we examined whether ERP components evoked by outcome feedback could serve as electrophysiological indices to examine the influence of current outcome evaluation on subsequent cooperative or aggressive decision-making. Thirty-four adult volunteers participated in a social game task, in which they were asked to choose between cooperation and aggression with an opponent player.Conventionally-averaged ERPs and temporospatial principal components analysis (PCA) factors were tested for their associations with subsequent decision-making. Results revealed that a central-parietal late positive potential (LPP) and central-parietal PCA factor approximating the classic LPP were related to changes of decision-making strategies on subsequent trials; however, the effect was significant only when the opponent selected 'cooperate' in the initial trial. The decision to cooperate in subsequent trials induced a larger LPP relative to the decision to aggress following opponent cooperation in the initial trial. Furthermore, we found that larger LPP amplitudes for an opponent's cooperative decision on the initial trial were associated with a higher probability of choosing cooperation on the subsequent trial. The results suggest that the amplitude of the central-parietal LPP is an electrophysiological index of the influence of initial outcome on subsequent social decision-making.