The importance of semantic network brain regions in integrating prior knowledge with an ongoing dialogue

To understand a dialogue, we need to know the topics that are being discussed. This enables us to integrate our knowledge of what was said previously, to interpret the current dialogue. This study involved a large-scale behavioural experiment conducted online and a separate fMRI experiment, both testing human participants. In both, we selectively manipulated knowledge about the narrative content of dialogues, presented in short videos. The clips were scenes from situation comedies that were split into two parts. The speech in the part 1 clips could either be presented normally or spectrally rotated to render it unintelligible. The part 2 clips that concluded the scenes were always presented normally. The behavioural experiment showed that knowledge of the preceding narrative boosted memory for the part 2 clips as well as increased the inter-subject semantic similarity of recalled descriptions of the dialogues. The fMRI experiment replicated the finding that prior knowledge improved memory for the conclusions of the dialogues. Furthermore, prior knowledge strengthened temporal inter-subject correlations in brain regions including the left angular (AG) and inferior frontal gyrus (IFG). Together, these findings show that, (1) prior knowledge constrains the interpretation of a dialogue to be more similar across individuals, and (2), consistent with this, the activation of brain regions involved in semantic control processing is also more similar between individuals who share the same prior knowledge. Processing in these regions likely supports the activation and integration of prior knowledge, which helps people to better understand and remember dialogues as they unfold.