Hanjun Liu

The prefrontal cortex has been implicated in the auditory-motor control of speech production. Recent evidence suggests the existence of prefrontally mediated mechanisms that exert inhibitory influence on compensatory adjustment of speech motor behaviors to prevent speech production from being excessively influenced by auditory feedback, but there is no direct evidence to support this hypothesis. In the present study, we applied a transcranial magnetic stimulation (TMS) protocol, continuous theta-burst stimulation (c-TBS), to depress activity in the left dorsolateral prefrontal cortex (DLPFC) as participants vocalized the vowel sounds while hearing their voice unexpectedly pitch-shifted +200 or +500 cents. Vocal and event-related potential responses to pitch perturbations were measured and compared between the c-TBS and sham conditions. Behaviorally, c-TBS over left DLPFC led to significantly larger vocal compensations than the sham condition. At the cortical level, however, significantly smaller P2 responses that were source localized in the left superior frontal gyrus and right supremarginal gyrus were found when participants received c-TBS over the left DLPFC as compared to the sham conditions. These findings demonstrate cTBS-induced effect of DLPFC on the neurobehavioral processing of vocal pitch regulation, suggesting that disrupting prefrontal function may impair top-down inhibitory control over compensatory vocal adjustment that leads to enhanced vocal compensations for feedback perturbations. This is the first study that provides direct evidence for a causal role of the prefrontal cortex in auditory feedback control of speech production.