Differential causal involvement of human auditory and frontal cortices in vocal motor control
Speech motor control requires integration of sensory and motor information. Bidirectional communication between frontal and auditory cortices is crucial for speech production, self-monitoring and motor control. We used cortical direct electrical stimulation (DES) to functionally dissect audio-motor interactions underlying speech production and motor control. Eleven neurosurgical patients performed a visually cued vocal task in which a short auditory feedback perturbation was introduced during vocalization. We evaluated the effect of DES on vocal initiation, voice fundamental frequency (F0) and feedback-dependent motor control. DES of frontal sites modulated vocal onset latencies. Stimulation of different inferior frontal gyrus sites elicited either shortening or prolongation of vocal latencies. DES distinctly modulated voice F0 at different vocalization stages. Frontal and temporal areas played an important role in setting voice F0 in the first 250 ms of an utterance, while Heschls gyrus was involved later when auditory input is available for self-monitoring. Vocal responses to pitch-shifted auditory feedback were mostly reduced by DES of non-core auditory cortices. Overall, we demonstrate that vocal planning and initiation are driven by frontal cortices, while feedback-dependent control relies predominantly on non-core auditory cortices. Our findings represent direct evidence of the role played by different auditory and frontal regions in vocal motor control.