Central Nervous System Control of breathing in Natural Conversational Turn-Taking

Discussion is a fundamental social activity requiring coordination of speech between interlocutors. Speech production is a complex human behaviour that involves several anatomo-physiological processes, including inspiration and expiration. The aim of the present study is to investigate the neurophysiological underpinnings of speech-related respiration events in conversational turn-taking. We made use of an existing corpus of natural conversations between a participant and its interlocutor (Human or Robot) focusing on synchronised (1) behavioural (conversation turn-taking), (2) respiratory (maxima of inspiration) and (3) neurophysiological (fMRI) data. Precisely timed conversation transcripts from 25 participants were used to categorise breathing maxima based on their timing relative to the participants speech onset. In agreement with the literature, the closest respiration time maximum to each speech turn occurred on average 200 ms prior to speech onset. The fMRI second-level contrast (pFWE 5 cm3) Resp+ (maximum respiration associated with speech) versus Resp-, exclusively masked to exclude speech related areas, revealed bilateral activations in the central sulcus, the brainstem and the cerebellum. The brainstem cluster comprises respiratory pattern generators, possibly the preBotzinger complex, that need to be inhibited to enslave breathing to speech production and not physiological needs, while the central sulcus cluster is likely to be located in the postcentral primary sensory cortex receiving upper torso inputs indicating that lungs are filled, and the cerebellum clusters could play a role in the timing of speech onset, 200 ms after a respiration maximum. These results show how cortical, cerebellar and brainstem coordinated control of breathing during conversational turn-taking is part of the intricate physiological mechanisms that contribute to natural communication dynamics.