Towards an understanding of somatosensory perturbation on covert speech production: a functional near infrared spectroscopy study.

INTRODUCTION

Recent initiatives have sought to understand the impact of somatosensory feedback during varying speech production tasks. The supramarginal gyrus (SMG) is a multi-function region that represents the somatosensory system and plays an essential role in the DIVA model via the generation and monitoring of novel motor commands. Here, we investigate the extent to which SMG activity is modulated via somatosensory perturbations (i.e., oral anesthesia via lidocaine and oral stimulation via lollipop) during covert production tasks.

METHODS

Thirty adult participants completed two covert production tasks: a spelling judgment task that emphasized stored speech patterns (stored articulation; e.g., bunt) and a sound judgment task that emphasized constructing a new speech pattern (assembled articulation; e.g., bont). The tasks were performed under three perturbation conditions: lidocaine, lollipop and no perturbation. Brain activity was measured as oxygenated hemoglobin levels using functional near-infrared spectroscopy from the left hemisphere SMG, inferior frontal gyrus, dorsolateral prefrontal cortex, and inferior temporal gyrus, representing somatosensory, speech motor planning, task control, and visual input regions, respectively.

RESULTS

The lollipop perturbation resulted in significantly higher activity, compared to the lidocaine, in the left SMG (p = 0.001), inferior frontal gyrus (p = 0.01) and dorsolateral prefrontal cortex (p = 0.01). In addition, the lollipop perturbation showed higher functional connectivity between left SMG-inferior frontal gyrus when compared to the lidocaine condition but only for the stored production task.

CONCLUSION

These findings provide evidence that the SMG is sensitive to alterations in oral sensory context even in the absence of overt articulation, supporting its proposed role within the DIVA model as a somatosensory state monitoring region that interacts with speech motor planning systems.

CLINICAL TRIAL REGISTRATION: https://clinicaltrials.gov/study/NCT05854082?term=lidocaine%20speech&rank=1, Identifier, NCT05854082.