Effect of recurrent laryngeal nerve paralysis on superior laryngeal nerve afferents during evoked vocalization.

We tested the hypothesis that vocal fold paresis leads to a substantial reduction in activity from the internal branch of the superior laryngeal nerve (iSLN) during respiration and evoked vocalization. The iSLN afferent activity was measured before and after recurrent laryngeal nerve paresis by cold block in decerebrate cats during spontaneous respiration and electrically evoked vocalization. Response rate patterns of 33 iSLN single units from 11 cats were categorized into 5 groups based on responses to vocalization. Only 24% of single units during spontaneous respiration and 18% during evoked phonation displayed activity pattern changes as a result of paresis. Those fibers affected were heterogeneous in discharge pattern, but none of the units that followed voice frequency lost this characteristic when the motor nerve was cooled. The relative insensitivity of iSLN activity to motor paralysis suggests that the receptors studied are coupled to tissue such that passive interaction rather than active muscular contraction is the major stimulus.