Previous studies find that the feedback-related negativity in brain potentials is sensitive to the negative outcome of one's own performance. The feedback-related negativity is suggested to reflect the learning processes using feedback about the consequences of recent actions. Learning can also take place when one observes other people's actions and the associated outcomes. We recorded brain potentials while the participant received outcome feedback for their own or for another person's performance in a gambling task. The feedback-related negativity or the feedback-related negativity-like effects were obtained in both situations, suggesting that similar neural mechanisms are involved in evaluating the outcomes of one's own and the other's actions. Thus, the neural processes in learning-by-observation resemble those in learning-by-doing.

Significance: Despite extensive research on disadvantageous inequity, little is known about advantageous inequity and whether these two types of inequity involve differential neurocognitive mechanisms. We address these questions from the perspective of context dependency and suggest that these two types of inequity are associated with differential neurocognitive substrates, subserved by different brain regions and in particular by the spatial gradient in insular activity. Our findings shed light on how social contexts (i.e., interpersonal guilt) are integrated into social decision making and suggest that the resistance to unequal situations when individuals are in disadvantageous status may primarily stem from their emotional responses, whereas the resistance to unequal situations when individuals are in advantageous status may involve advanced cognitive functions such as mentalizing.

Previous studies have shown that social comparison influences individual’s fairness consideration and other-regarding behavior. However, it is not clear how social comparison affects the brain activity in evaluating fairness during asset distribution. In this study, participants, acting as recipients in the ultimatum game, were informed not only of offers to themselves but also of the average amount of offers in other allocator–recipient dyads. Behavioral results showed that the participants were more likely to reject division schemes when they were offered less than the other recipients, especially when the offers were highly unequal. Event-related brain potentials recorded from the participants showed that highly unequal offers elicited more negative-going medial frontal negativity than moderately unequal offers in an early time window (270–360 ms) and this effect was not significantly modulated by social comparison. In a later time window (450–650 ms), however, the late positive potential (LPP) was more positive for moderately unequal offers than for highly unequal offers when the other recipients were offered less than the participants, whereas this distinction disappeared when the other recipients were offered the same as or more than the participants. These findings suggest that the brain activity in evaluating fairness in asset division entails both an earlier (semi-) automatic process in which the brain responds to fairness at an abstract level and a later appraisal process in which factors related to social comparison and fairness norms come into play.

People feel bad for inflicting harms upon others; this emotional state is termed interpersonal guilt. In this study, the participant played multiple rounds of a dot-estimation task with anonymous partners while undergoing fMRI. The partner would receive pain stimulation if the partner or the participant or both responded incorrectly; the participant was then given the option to intervene and bear a proportion of pain for the partner. The level of pain voluntarily taken and the activations in anterior middle cingulate cortex (aMCC) and bilateral anterior insula (AI) were higher when the participant was solely responsible for the stimulation (Self_Incorrect) than when both committed an error (Both_Incorrect). Moreover, the gray matter volume in the aMCC predicted the individual’s compensation behavior, measured as the difference between the level of pain taken in the Self_Incorrect and Both_Incorrect conditions. Furthermore, a mediation pathway analysis revealed that activation in a midbrain region mediated the relationship between aMCC activation and the individual’s tendency to compensate. These results demonstrate that the aMCC and the midbrain nucleus not only play an important role in experiencing interpersonal guilt, but also contribute to compensation behavior.