Abstract
The ultimatum game is a stylized game to study decision making in which a proposer suggests how to split a sum of money either fairly or unfairly. Unfair splits are often rejected by the responder even at a personal cost. Previous research using unspecific stimulus-onsets suggests that such rejections are of cortical origin and involve a change of feeling states. Using an fMRI-design to specifically study early emotional components of decision making and a pharmacological intervention we demonstrate a causal role of the limbic system in the act of rejection. In the placebo-treated group rejection was directly linked to an increased amygdala activity and benzodiazepine treatment decreased rejection rate concomitantly with a suppressed amygdala response to unfair proposals in spite of an unchanged feeling of unfairness. Thus, we segregate the neural basis of rejections associated with the initial reactive emotional response from the slower affective processing associated with awareness.