Lip Muscle EMG Responses to Oral Pressure Stimulation

Sinusoidal intraoral pressure changes having peak-to-peak amplitudes of 2-6 cmH2O were applied at frequencies of 2-14 Hz. Reflex responses were observed in the lip muscle EMG of all 6 subjects tested. Across subjects, the phase shift of EMG responses varied in a linear manner with stimulus frequency. This suggests that responses were mediated over a reflex pathway having a relatively fixed response latency. Step-like changes in oral pressure produced a consistent excitatory response having a latency of 30-35 ms. The fact that reflexes may be elicited in lip muscles with oral pressure changes similar to those occurring in speech increases the likelihood that mechanoreceptor responses to intraoral pressure changes are involved in sensorimotor integration for speech production.