The neural representation of mental beliefs held by two agents.

Neuroimaging research has demonstrated that mentalizing about false beliefs held by other people recruits the temporo-parietal junction (TPJ). However, earlier work was limited to a single agent that held a false belief. We investigated the effect of two agents that held similar or mixed false and/or true beliefs. Participants saw animated stories with two smurfs holding true or false beliefs (Story phase). At the end of each trial, they were requested to take the perspective of the self or one of the smurfs (Question phase). We predicted that an increasing number of smurfs holding a false belief would increase activation in the TPJ when participants have to report the belief of the smurf, because the incongruent belief should have a stronger influence if it is held by two compared with one agent. This prediction was confirmed as activation in the TPJ during the Story and Question phase increased when more smurfs held a false belief. Taking the perspective of the self led to stronger activation of the TPJ in the two conditions that involved a true belief and weakest activation in the condition of two false beliefs. These data suggest that activation in TPJ depends on the perspective participants take, and that the number of agents holding a false belief influences activation in the TPJ only when taking the agent's perspective.