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Pars opercularis underlies speech motor efference copy and successful auditory feedback processing: Evidence from left-hemisphere stroke
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Poster A67 in Poster Session A, Tuesday, October 24, 10:15 am - 12:00 pm CEST, Espace Vieux-Port
Sara D. Beach1, Ding-lan Tang1, Swathi Kiran2, Caroline A. Niziolek1; 1University of Wisconsin–Madison, 2Boston University
Hearing one’s own speech allows for acoustic self-monitoring in real time. Left inferior-frontal brain regions are thought to give rise to efferent predictions of the sensory consequences of speech motor acts. These efference copies are then thought to be compared to true auditory feedback in superior temporal cortex, causing suppression of the neural response when there is a match, and reduced suppression when there is a mismatch. Reduced suppression is therefore a candidate neural signal driving online correction of deviant speech sounds. The present study assessed the integrity of this circuit in persons with aphasia (PWA) with lesions in the territory of the left middle cerebral artery. We recorded MEG while 15 PWA and age-matched controls spoke monosyllabic words and listened to playback of their utterances. We measured suppression of the M100 neural response in the speaking condition (with an efference copy) relative to the listening condition (without an efference copy) in left and right hemispheres and related it to lesion profiles and speech behavior. We found that bilateral speaking-induced suppression, comparable to controls’, was maintained despite large left-hemisphere lesions. PWA with more spared tissue in left pars opercularis had greater left-hemisphere neural suppression and greater behavioral correction of deviant, atypical pronunciations (“vowel centering”), whereas sparing of the left superior temporal gyrus was not related to either neural suppression or acoustic behavior. In turn, PWA who made greater acoustic corrections had fewer overt speech errors in the MEG task, suggesting that vowel centering is related to successful production. Overall low signal in lesioned left hemispheres precluded analysis of the direct relationship between reduced suppression and correction of deviant productions, but we replicated a prior finding that cortical sensitivity to self-produced vowel typicality is a left-lateralized phenomenon. We did not find evidence that lesions drove neural plasticity in the right hemisphere in terms of response amplitude, suppression, or sensitivity. Together, these results suggest that some degree of efference copy-mediated neural suppression can survive damage to left-hemisphere motor- and speech-related regions, but that pars opercularis plays a significant role in the magnitude of that suppression, with putative consequences for the ability of PWA to successfully process and limit variation in their own speech.
Topic Areas: Speech Motor Control, Disorders: Acquired