The motor cortex is involved in reflexive compensatory adjustment of speech articulation

Although speech articulation relies heavily on the sensorimotor processing, little is known about its brain control mechanisms. Here, we investigate, using transcranial magnetic stimulation, whether the motor cortex contributes to the generation of quick sensorimotor responses involved in speech motor coordination. By applying a jaw-lowering perturbation, we induced a reflexive compensatory upper-lip response, which assists in maintaining the intact labial aperture in the production of bilabial fricative consonants. This reflex response was significantly facilitated by subthreshold transcranial magnetic stimulation over the motor cortex, whereas a simple perioral reflex that is mediated only within the brainstem was not. This suggests that the motor cortex is involved in generating this functional reflexive articulatory compensation.