Neural responses of in-group "favoritism" and out-group "discrimination" toward moral behaviors.

People hate being deceived. However, what would it be if lies come from in-group members compared with that from out-group members? In the current Electroencephalography (EEG) study, we recruited thirty-six participants to play a modified estimator and advisor game to investigate the mental and neural processes to lies and truth conveyed by in-group and out-group members. At the behavioral level, lies are less morally acceptable, arose less positive emotion, and made participants distribute less money to the advisor in a dictator game. Meanwhile, participants liked the in-group university more than the out-group university and they thought they were more similar to in-group members than to out-group members. However, there were no significant interactions of group type (i.e., in-group and out-group) and message type (i.e., lies and truth) in the aforementioned behavioral assessments. At the neural level, significant interaction effects were found in the parietal N1 and P3 amplitude. More importantly, no significant N1 and P3 amplitude differences between in-group lies and truth were found, while outgroup lies elicited larger P3 amplitude than outgroup truth and out-group truth elicited larger N1 amplitude than outgroup lies. What's more, P3 amplitude differences between lies vs. truth positively correlated with fairness scores only in the in-group condition but not in the out-group condition. Current study showed that the P3 component was sensitive in capturing subtle differences when participants were processing different types of lies and truth that could not be captured by behavioral measurements. Besides, the fairness trait modulated the in-group bias related P3 patterns. The current study provides insight into the neurobiological mechanism underlying the mental process of in-group and out-group lies and truth, and suggests individuals' tendency of general in-group favoritism and out-group discrimination toward moral behaviors.