Functional roles of the superior laryngeal nerve afferents in electrically induced vocalization in anesthetized cats

Our purpose was to elucidate the functional roles of the laryngeal afferents in controlling vocalization. We investigated the effects of laryngeal deafferentation (sectioning the internal branch of the superior laryngeal nerve (ISLN)) on respiration and voice quality during electrically-induced vocalization in twelve ketamine anesthetized cats. Co-ordinated vocal activity was obtained by electrical stimulation to the pontine call site. After the bilateral ISLN section, the respiratory, expiratory and inspiratory durations during induced vocalization became 0.56 +/- 0.15, 0.44 +/- 0.12 and 0.67 +/- 0.19 (mean +/- S.D., n = 9) times, respectively, compared with those before the ISLN section. A decrease in respiratory duration was also observed when local anesthetics were applied to the laryngeal mucosa. The laryngeal deafferentation increased the degree of hoarseness with a decrease in the fundamental frequency. Since the laryngeal deafferentation caused a decrease in the intralaryngeal adductor activities, it was suspected that the voice quality change was partly caused by the reduction in adductor activities. It was thus concluded that feedback via laryngeal afferents plays an important role in controlling vocalization.