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Human sensorimotor cortex control of directly-measured vocal tract movements during vowel production.

J Neurosci. 2018 Feb 08;:

Authors: Conant DF, Bouchard KE, Leonard MK, Chang EF

During speech production, we make vocal tract movements with remarkable precision and speed. Our understanding of how the human brain achieves such proficient control is limited, in part due to the challenge of simultaneously acquiring high-resolution neural recordings and detailed vocal tract measurements. To overcome this challenge, we combined ultrasound and video monitoring of the supralaryngeal articulators (lips, jaw and tongue) with electrocorticographic (ECoG) recordings from the cortical surface of 4 subjects (three female, one male) to investigate how neural activity in the ventral sensory motor cortex (vSMC) relates to measured articulator movement kinematics (position, speed, velocity, acceleration) during the production of English vowels. We found that high-gamma activity at many individual vSMC electrodes strongly encoded the kinematics of one or more articulators, but less so for vowel formants and vowel identity. Neural population decoding methods further revealed the structure of kinematic features that distinguish vowels. Encoding and decoding of articulator kinematics was sparsely distributed across time, and primarily occurred during the time of vowel onset and offset. In contrast, encoding was low during the steady state portion of the vowel, despite sustained neural activity at some electrodes. Significant representations were found for all kinematic parameters, but speed was the most robust. These findings enabled by direct vocal tract monitoring demonstrate novel insights to the representation of articulatory kinematic parameters encoded in the vSMC during speech production.SIGNIFICANCE STATEMENTSpeaking requires precise control and coordination of the vocal tract articulators (lips, jaw, and tongue). Despite this impressive proficiency, our understanding of how the brain achieves such control is rudimentary, in part because the movements themselves are difficult to observe. By simultaneously measuring speech movements and the neural activity that gives rise to them, we demonstrate how neural activity in sensorimotor cortex produces complex, coordinated movements of the vocal tract.

PMID: 29439164 [PubMed – as supplied by publisher]