Coactivation of the Laryngeal Muscles in Pigs Without External Neural Control Indicates Existence of an Intrinsic Neuronal Network.

Electrophysiological studies of the larynx expose the mechanisms by which voice production is controlled. Previous studies have revealed certain phenomena during laryngeal oscillations that suggest a complex control mechanism. Starting from the principle of agonist-antagonist muscular pairing, the aim of this study was to gain a deeper insight into the function of the cricothyroid (CT) and thyroarytenoid (TA) muscles, both central to voice production. Electromyographic recordings were used to determine the response of the two muscles to different stimulation situations in an ex vivo animal model of the denervated larynx of pigs (n=26). Using a set of different experiments, it was shown that when one muscle (CT or TA muscle) was electrically stimulated, a response was observed in the other muscle, which in the otherwise-denervated larynx, was caused only by the applied stimulation and exhibited the characteristics of compound action potentials. This response was reproducible in all larynxes examined and was present bidirectionally. No response was registered in the absence of stimulation. The results show the existence of coactivation of the CT and TA muscles in the absence of external innervation hinting at the presence of a localized neuronal network of the larynx that has not been described previously. Further morphological investigation is needed to determine the presence of this internal laryngeal neuronal network.