Finding your way in the zoo: How situation model alignment affects interpersonal neural coupling

INTRODUCTION: We investigated how speaker-listener alignment at the level of the situation model is reflected in inter-subject correlations in temporal and spatial patterns of brain activity, also known as between-brain neural coupling (Stephens et al., 2010). We manipulated the complexity of the situation models that needed to be communicated (simple vs complex situation model) to investigate whether this affects neural coupling between speaker and listener. Furthermore, we investigated whether the degree to which alignment was successful was positively related to the degree of between-brain coupling. METHOD: We measured neural coupling (using fMRI) between speakers describing abstract zoo maps, and listeners interpreting those descriptions. Each speaker described both a ‘simple’ map, a 6x6 grid including five animal locations, and a ‘complex’ map, an 8x8 grid including 7 animal locations, from memory, and with the order of map description randomized across speakers. Audio-recordings of the speakers’ utterances were then replayed to the listeners, who had to reconstruct the zoo maps on the basis of their speakers’ descriptions. On the group level, we used a GLM approach to model between-brain neural coupling as a function of condition (simple vs complex map). Communicative success, i.e. map reproduction accuracy, was added as a covariate. RESULTS: Whole brain analyses revealed a positive relationship between communicative success and the strength of speaker-listener neural coupling in the left inferior parietal cortex. That is, the more successful listeners were in reconstructing the map based on what their partner described, the stronger the correlation between that speaker and listener's BOLD signals in that area. Furthermore, within the left inferior parietal cortex, pairs in the complex situation model condition showed stronger between-brain neural coupling than pairs in the simple situation model condition. DISCUSSION: This is the first two-brain study to explore the effects of complexity of the communicated situation model and the degree of communicative success on (language driven) between-brain neural coupling. Interestingly, our effects were located in the inferior parietal cortex, previously associated with visuospatial imagery. This process likely plays a role in our task in which the communicated situation models had a strong visuospatial component. Given that there was more coupling the more situation models were successfully aligned (i.e. map reproduction accuracy), it was surprising that we found stronger coupling in the complex than the simple situation model condition. We plan in ROI analyses in primary auditory, core language, and discourse processing regions. The present findings open the way for exploring the interaction between situation models and linguistic computations during communication