Search Abstracts | Symposia | Slide Sessions | Poster Sessions
The causal role of the mPrCG in speech-motor sequencing
Poster Session C, Friday, October 25, 4:30 - 6:00 pm, Great Hall 3 and 4
Jessie R. Liu1, Lingyun Zhao1, Patrick W. Hullett1, Edward F. Chang1; 1University of California San Francisco
Fluent speech production requires the planning and articulation of accurately sequenced speech sounds. Though Broca’s area has traditionally been thought to facilitate speech sequencing, recent studies have shown that damage to Broca’s area does not often cause chronic speech production deficits. This has left the question of what neural populations causally control speech-motor sequencing unresolved. To address this, we used high-density direct cortical recordings while participants spoke utterances with varying syllabic sequence complexity. We identified a distributed cortical network with sustained activity modulated by the complexity of the sequences, across multiple speech areas including Broca’s area and the posterior superior temporal gyrus, but strongest in the middle precentral gyrus (mPrCG). Only neural activity in the mPrCG both scaled with sequence complexity and predicted reaction time, suggesting that while other areas may be involved in higher level speech processing, the mPrCG may play a role in the motoric aspect of speech sequencing. To test whether the mPrCG is causally involved in speech-motor sequencing, we applied direct electrocortical stimulation to several areas whose neural activity was modulated by sequence complexity, while participants spoke a variety of speech sequences. We found that only stimulation in the mPrCG, and not Broca’s area, caused speech disfluencies only when participants spoke complex speech sequences (like “catastrophe”), but not during simple sequences (like “papapa”). Disfluencies included increased syllable durations, increased syllable segmentation, distortions, and stuttering. Control trials ruled out other stimulation effects, such as anomia or speech arrest, as drivers of these errors. Together, these results show that stimulation of the mPrCG results in speech disfluencies resembling those of apraxia of speech, a clinical speech disorder of speech-motor sequencing and programming. In summary, we demonstrate the critical role of the mPrCG in speech-motor sequence planning and establish a neurophysiological link between speech sequencing, the mPrCG, and apraxia of speech. These results further our understanding of speech-motor sequencing and stress the necessity of accounting for the mPrCG in models of speech production.
Topic Areas: Speech Motor Control, Disorders: Acquired