Access to others’ internal monologues aligns neural processing of narratives and trait impressions

Inferring others’ thoughts is a challenging task, but the results of such inferences play major roles in everyday interactions. Prior research has shown that knowledge of others’ mental states informs judgements of their personalities and future behavior. However, such studies have faced a tradeoff between internal and external validity, which has made it difficult to differentiate the inference of mental states from the process of using mental state knowledge. This study uses films featuring internal monologue narration – spoken audio representing what a character is thinking – to overcome this challenge. In each of two films, we identified clips featuring internal monologues and silenced different halves of these clips to create two versions of the same film with different mental state content. Participants were randomly assigned to watch one version of each film in the fMRI scanner (N = 28) or online (N = 200), with the latter making ratings of the main characters’ traits throughout the film. We find that access to the same mental state information aligns participants’ brain activity while listening to monologues and in subsequent clips. This suggests that the context of knowing the characters’ thoughts shapes narrative processing. Internal monologues also causally shaped online ratings of characters’ traits and correlated neural pattern similarities that emerged spontaneously in the brains of scanner participants. Effects were observed across lateral temporal cortex, as well as in prefrontal and parietal regions. Together these findings show how mental state knowledge, independent of inference, shapes downstream social cognition in naturalistic contexts.