In everyday life, expert advice has a great impact on individual decision making. Although often beneficial, advice may sometimes be misleading and cause people to pursue actions that entail suboptimal outcomes. This detrimental effect may diminish over time, when individuals have gathered sufficient contradicting evidence. Given the strong influence initial information has on opinion and personality impression formation, we aimed to investigate whether initial advice-confirmatory experience potentiates the rigidity with which persons stick to misleading advice. Furthermore, we intended to characterize the neuronal basis of such putative primacy effect. While undergoing functional magnetic resonance imaging (fMRI), participants selected between probabilistically reinforced symbols and were given the misleading tip that two low-probability symbols had a high reinforcement probability. One of these symbols initially received manipulated advice-congruent positive feedback (PF), the other one advice-incongruent negative feedback. Behaviorally, participants were impaired at learning to avoid advice-receiving symbols and overvalued them in terms of willingness to pay (WTP) in an auction market. Crucially, initial PF potentiated all effects. Greater ventral pallidal response to initial but not later PF during learning predicted higher behavioral WTP. Our results demonstrate that the nature of the very first advice-related experience already determines how strongly misleading advice will influence learning and ensuing decision making-an effect that is mediated by the ventral pallidum. Thus, in contrast to conventional reinforcement learning, learning under the influence of advice is susceptible to primacy effects. The present findings advance our understanding of why false beliefs are particularly difficult to change once they have been reinforced.
