Shared contextual knowledge strengthens inter-subject synchrony and pattern similarity in the semantic network

Understanding what is happening during an event can be helped by prior knowledge of the specific context. However, the effect of contextual knowledge on neural representations of events, and relatedly, how shared knowledge impacts on the similarity of neural processing of events across individuals is poorly understood. To investigate this, we manipulated the availability of knowledge about the narrative content of events while keeping all other aspects equally familiar. The presence of narrative knowledge boosted subjective ratings of coherency and objective measures of memory performance. Narrative knowledge had two effects on fMRI markers of neural processing: (1) it strengthened temporal inter-subject correlations in ventromedial prefrontal cortex as well as left angular and inferior frontal gyri, and (2) it also increased spatial inter-subject pattern similarity in the bilateral anterior temporal lobes. We propose that shared narrative knowledge constrains participants9 interpretation of the videos and thereby results in greater alignment of neural processing of the events. We propose a division of labour between semantic control brain regions (VMPFC, IFG and AG), which process the moment-by-moment content of the narrative, and the ATL which represents the overarching narrative gist of an event.