The role of inferior frontal gyrus in rapid conversational turn-taking

Abstract

During conversation, speaker overlap is avoided while inter-turn silence is minimized. Notably, inter-speaker gaps are typically 200 ms or less—shorter than what is required to plan single words—suggesting that considerable speech planning (SP) occurs as speakers listen to their partners’ turns. Though the psycholinguistic mechanisms of SP during turn-taking are well-studied, its neural dynamics are largely unknown. Using intracranial electrocorticography, we delineate SP-related activity from that of sensorimotor processes using questions (adapted from Bogels et al., 2015) where the critical-information (CI) required to answer is provided at a singular timepoint. Consistent with involvement in SP, we observe that the left inferior frontal gyrus (IFG) is active immediately following CI. We also observe that IFG is preferentially active during SP but not general motor planning. Furthermore, we find that a subset of IFG planning sites are active during natural conversation while patients listen to the turns of opposing speakers. Finally, in preliminary experiments where IFG is stimulated while patients answer CI-questions, we find that IFG disruption results in significantly longer reaction times and lexical errors but not gross articulatory disruptions. In conclusion, we demonstrate that a subregion of IFG is critical for the SP processes employed during rapid conversational turn-taking.