Unforgettable ultimatums? Expectation violations promote enhanced social memory following economic bargaining

Recent work in the field of neuroeconomics has examined how people make decisions in interactive settings. However, less is currently known about how these social decisions influence subsequent memory for these interactions. We investigated this question by using functional magnetic resonance imaging to scan participants as they viewed photographs of people they had either recently played an Ultimatum Game with in the role of Responder, or that they had never seen before. Based on previous work that has investigated "cheater detection", we were interested in whether participants demonstrated a relative enhanced memory for partners that made either fair or unfair proposals. We found no evidence, either behaviorally or neurally, supporting enhanced memory based on the amount of money offered by the Proposer. However, we did find that participants' initial expectations about the offers they would experience in the game influenced their memory. Participants demonstrated relatively enhanced subjective memory for partners that made proposals that were contradictory to their initial expectations. In addition, we observed two distinct brain systems that were associated with partners that either offered more or less than the participants' expectations. Viewing pictures of partners that exceeded initial expectations was associated with the bilateral anterior insula, anterior cingulate cortex/premotor area, striatum, and bilateral posterior hippocampi, while viewing partners that offered less than initial expectations was associated with bilateral temporal-parietal junction, right STS, bilateral posterior insula, and precuneus. These results suggest that memory for social interaction may not be guided by a specific cheater detection system, but rather a more general expectation violation system.