JAMES C. L. LI, MD
NEW YORK, NEW YORK

RICK M. ROARK, PHD; STEVEN D. SCHAEFER, MD
VALHALLA, NEW YORK

ALEXANDER ADAM, MS
BOSTON, MASSACHUSETTS

Decomposition of an electromyographic signal into its constituent motor unit action potentials provides specific information about how laryngeal muscle force is controlled by the central nervous system, in terms of the recruitment and firing rate of individual motor units. Herein presented are the first recordings and analyses of multiple motor unit activations in the larynx. We used a quadrifilar needle electrode to record electromyographic signals from the thyroarytenoid muscle of normal subjects during tasks ranging from quiet breathing to a short sentence. Motor unit action potentials were identified and tracked throughout the task productions by means of pattern-recognition and decomposition software. The interfiring intervals and mean firing rates were plotted for each identified motor unit. Motor unit recruitment and decruitment patterns were noted. This study provides new information about the neuromuscular physiology of the larynx, specifically, the recruitment and decruitment patterns of multiple motor units, the synchrony of motor unit activation, and the existence of a common drive control from the central nervous system. These observations are fundamental to understanding various laryngeal disorders (eg, vocal fold paresis, spasmodic dysphonia) in which there appears to be a breakdown of neuromuscular control.