Functions of the right DLPFC and right TPJ in proposers and responders in the ultimatum game

Abstract

Recent studies explored a network of brain regions involved in economic decision making. The present study focuses on two of those regions, each relevant for specific and distinct functions in economic decision making: the right temporoparietal junction (rTPJ) and the right dorsolateral prefrontal cortex (rDLPFC). In two experiments using transcranial direct current stimulation, we explored two proposed functions of these areas in bargaining situations using the ultimatum game (UG): understanding the others perspective and integration of fairness norms. Participants first took the role of the proposer and then the role of the responder. We showed that stimulation of the rTPJ only affected the proposer condition. Interestingly, inhibition of the rTPJ led to fairer offers, which strengthens the view that the role of the rTPJ in bargaining situations is to differentiate one's own from the other's perspective. Furthermore, we argue that the rDLPFC is most likely involved in suppressing self-interest when a person is confronted with a direct reward but does not play a role in long-term reward anticipation or integrating social fairness norms. We conclude that self-interest inhibition is shown only in responders, and that perspective taking seems to be a necessary specifically for proposers in the UG.

Keywords: perspective taking; self-other-distinction; self-regulation; tDCS.

Fig. 1

Depiction of the trial structure. Participants assumed the role of the proposer (upper) as well as in the role of responders (lower). Time scale is in milliseconds. Bold numbers represent fixed time windows. A tilde indicates a randomised time period and a ‘max’ indicates the maximum time participants had to react before the computer forced them to give the full amount of MU (proposer condition) or accept any amount from the other player (responder condition).

Fig. 2

All error bars indicate ±1 Standard error (SE). Asterisks indicate P < 0.05. For proposers, (A) there was a significant difference between cathodal stimulation and anodal and sham stimulation in the effect on the average amount of money kept in the rTPJ stimulation groups. (B) There was no significant effect of stimulation condition on the average amount of money kept over 10 rounds in the rDLPFC stimulation groups. For responders, (C) there was no effect when rTPJ was stimulated. (D) There was a significant difference between cathodal stimulation and anodal and sham stimulation in the effect on the total number of offers accepted by responders.