Responding to Unfair Offers Made by a Friend: Neuroelectrical Activity Changes in the Anterior Medial Prefrontal Cortex

In economic exchange games, unfair offers normally evoke more negative-going MFN responses compared with fair offers (Boksem and De Cremer, 2010; Hewig et al., 2011; Wu et al., 2011b). Campanha et al. (2011) replicated this effect for offers from a stranger, but reported a reversed pattern for offers from a friend. They suggested that friendship functions as a buffer to counteract the "social pain" induced by unfairness. These findings, however, sharply contrast with Wu et al. (2011a) who demonstrated that the MFN effect appears for offers from friends but not for offers from strangers.

When we compare the two studies, we can see two differences in the procedures. First, the economic games used in the studies differ: the ultimatum game in Campanha et al. (2011) vs. the dictator game in Wu et al. (2011). In the ultimatum game, the responder (i.e., the participant) can reject an offer by the proposer, leading to a zero outcome for both the responder and the proposer. Note that, Campanha et al. (2011) did not differentiate ERP responses to offers rejected from offers accepted. In the dictator game, however, the responder has no right to reject the offer and has to accept it. It is not certain to what extent the offers in the two games would evoke different patterns of MFN effect although Hewig et al. (2011) did report that offers in the two games elicited similar patterns of brain responses.

The second, and most crucial difference, is that Campanha et al. (2011) used only one friend (and one stranger) to pair with one participant, making it very clear with whom the participant was interacting. In contrast, Wu et al. (2011) used two friends (and two strangers) to pair with one participant and it was made sure that the participant could not know exactly with whom he was interacting in a particular trial.

We argue that, compared to the Wu et al (2011a) study, in Campanha et al. (2011), it was likely that in responding to offers from the friend, the participant was more concerned with the maintenance of a long-term friendship and his brain responses to (un-)fair offers could have been affected by this "strategic" consideration. In other words, the participant was future-focused in considering offers from the friend and this orientation could have masked or inhibited his more impulsive responses to (un-)fair offers. Wu et al. (2011) allowed the participant to express his degree of satisfaction towards the offer on a visual analogue scale in each trial. Importantly, this rating information was not communicated to the proposer. The rating data indicated that participants were more unsatisfied with unfair offers from friends than unfair offers from strangers. This pattern is inconsistent with the subjective rating of fairness of offers in Campanha et al. (2011): unfair offers from the friend was rated as less unfair than unfair offers from the stranger. [However, the rating in Campanha et al. (2011) was a post-experiment one, i.e., after all trials, making it susceptible to more deliberate consideration]. The MFN responses to offers from friends in Wu et al. (2011) may be attributed to the participant's more automatic, uninhibited responses to the violation of social norms associated with friendship (e.g., "I should be treated more favorably by my friend than by a stranger").

The absence of a significant MFN effect for the stranger condition in Wu et al. (2011a) was interpreted as reflecting the change of context (i.e., the differentiation between ingroup and outgroup) and its subsequent impact upon the responder's expectancy towards fairness of offers from strangers. However, it is not entirely clear how the fair offers from a friend could be treated as negative social feedback, compared with the unfair offers from the friend, and elicit more negative- going MFN responses (Campanha et al., 2011). Was it because the responder cared so much about future interaction with the friend that he would rather prefer the friend to retain a larger proportion of the asset and to be nice or generous towards the responder in future? Further studies are needed to replicate this finding.

References

Boksem MAS, De Cremer D (2010) Fairness concerns predict medial frontal negativity amplitude in ultimatum bargaining. Soc Neurosci 5:118- 128.

Campanha C, Minati L, Fregni F, Boggio PS (2011) Responding to unfair offers made by a friend: neuroelectrical activity changes in the anterior medial prefrontal cortex. J Neurosci 31:15569-15574.

Hewig J, Kretschmer N, Trippe RH, Hecht H, Coles M, Holroyd CB, Miltner WH (2011) Why humans deviate from rational choice. Psychophysiology 48:507-514.

Wu Y, Leliveld MC, Zhou X (2011a) Social distance modulates recipient's fairness consideration in the dictator game: an ERP study. Biol Psychol 88:253-262.

Wu Y, Zhou Y, van Dijk E, Leliveld MC, Zhou X (2011b) Social comparison affects brain responses to fairness in asset division: an ERP study with the ultimatum game. Front Hum Neurosci 5:131.

Conflict of Interest:

None declared