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Cortical dynamics underlying speech sequence planning
Poster A71 in Poster Session A, Tuesday, October 24, 10:15 am - 12:00 pm CEST, Espace Vieux-Port
Jessie R. Liu1,2, Lingyun Zhao1, Patrick W. Hullett1, Edward F. Chang1,2; 1University of California San Francisco, 2University of California Berkeley - University of California San Francisco Graduate Program in Bioengineering
Fluent speech production requires the planning and articulation of accurately sequenced speech sounds. This process is commonly thought to result from the progression of activity across cortical areas, each of which has a specific function in the planning and execution of articulation. The classic model is that Broca’s area sends planning commands to the precentral gyrus which in turn sends motor commands to the vocal tract. However, recent evidence suggests that Broca's area is not critical for articulation, and the neurological basis of how speech is sequenced is unknown. To address this, we used high-density direct cortical recordings (electrocorticography) from distributed speech cortical areas to investigate the dynamics of cortical activity while participants were cued to read, wait a short delay, and speak simple or complex syllable sequences. While we found activity related to execution and feedback, we found unexpectedly prominent sustained activity across multiple cortical areas that lasted throughout all periods of the task. Sustained activity was found in the middle precentral gyrus (mPrCG), posterior superior temporal gyrus, supplementary motor area, supramarginal gyrus, and the inferior and middle frontal gyri. Sustained neural activity reflected distinct internal states that transition between the encoding, delay, pre-speech, and execution periods. Trial-averaged sustained population activity also showed distinct trajectories associated with each of these task phases. Encoding and execution period trajectories occupied roughly 2D planes, which were not parallel to each other, suggesting that activity prior to production does not directly trace the eventual neural trajectory associated with execution. Increased sequence complexity was associated with greater sustained activity, most prominently in the mPrCG. Pre-speech activity in the mPrCG also correlated with behavior, predicting single trial reaction times. These results suggest that speech production planning is dependent upon sustained cortical dynamics supporting speech sequence execution. Importantly, we identify the mPrCG as a novel and critical node of speech-motor planning.
Topic Areas: Speech Motor Control, Language Production