Neural mechanisms for stopping ongoing speech production

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Project Summary Speech production is timed precisely during conversations. People demonstrate a remarkable ability to adjust the start and stop time of their speech depending on what others say. The long-term goal of the proposed work is to understand the neural mechanism that gives rise to the precise control of speech timing during conversations. Specifically, this proposal focuses on the control for quickly stopping an ongoing production before an utterance is finished. Neural circuits involved in speech production are found across many cortical areas, such as the sensorimotor cortex, the premotor and prefrontal cortices. Existing evidence has shown how these circuits support the generation of speech sound. For example, the ventral part of the sensorimotor cortex (vSMC) contains a representation of articulators (e.g., lip, jaw, tongue). Neural activity in vSMC encodes the articulatory kinematic trajectories during speaking. However, little is known about the neural circuit controlling a sudden stop of speech. This knowledge gap limits our understanding of the principles underlying normal speech production, as well as the causes of speech and communication disorders like stuttering and aphasia. The proposal will test the overarching hypothesis that the premotor areas contain a neural network that distinguishes sensory inputs indicating a stop and generates signals to modulate vSMC for stopping. The premotor areas provide input to the vSMC and serve important functions in speech preparation and sensorimotor transformation. Dr. Zhao will incorporate high-density electrocorticography (ECoG) to record neural activities directly from the human cortex while participants perform speech production tasks. High-density ECoG is a state- of-the-art technique with fine spatial and temporal resolutions that are well suited for studying the neural dynamics of speech. Aim 1 will define the premotor signal for the control of speech stopping. Participants are instructed to make intermittent stops during speech production following visual cues. Aim 2 will determine the effect of stop activity on articulatory control during stopping. Dr. Zhao will obtain knowledge of articulatory phonetics and psycholinguistics, and the experimental techniques to measure articulatory kinematic features during speech stopping. Aim 3 will determine the role of the premotor network for stopping in conversation contexts. The outcome of this project is expected to provide basic knowledge for understanding the normal function of speech production, which is necessary for improving treatments for speech and communication disorders in the future. Dr. Zhao will be supported by a top-tier academic environment and world-class experts at University of California, San Francisco, and University of California, Berkeley. This grant will provide training opportunities of human cortical neurophysiology and skills in linguistics, which will facilitate his smooth transition to an independent investigator.