Effects of External Mechanosensory Stimulation on Laryngeal Neuromuscular Activity
T Loucks, C Poletto, K Saxon, C Ludlow
We applied rapid external mechanical stimulation that compressed the thyroid cartilage to test whether reflex responses could be elicited from the intrinsic laryngeal muscles in six healthy human volunteers. The stimulus elicited short-latency surface EMG responses and characteristic changes in fundamental frequency (F0) during high-pitch phonation, which replicated a previous study (Sapir, Baker, Larson and Ramig, 2000). However, the previous study did not record from the intrinsic laryngeal muscles so it was not possible to determine if the muscle responses and F0 changes were related to intrinsic laryngeal muscle activity. Hooked-wire electrode recordings from the thyroarytenoid and cricothyroid muscles in the current study indicated reflex responses were not elicited in any subjects. Rather, robust reflex responses were recorded in four subjects from hooked-wire electrodes in the sternothyroid muscle. The latency of the sternothyroid response corresponded to the latency of the surface EMG response, which suggests the surface EMG was detecting sternothyroid activity. The pattern of the F0 responses and muscle responses did not show an obvious relationship, which suggests the F0 changes may be a mechanical effect occuring within the same latency window unrelated to stretch-induced sternothyroid responses.