EMG Activities of the Intralaryngeal and Ventilatory Muscles During Electrically Induced Vocalization in Decrebrate Cats

Vocalization was induced by repetitive electrical stimulation (0.2ms , 25 to 80 ji A, 60 to 100Hz, lasting for 5 to 30 s) delivered to the brainstem (Horsley Clarke coordinates: A 1.5 to P 5.0, L or R 1.5 to 5.5, H -3.0 to -9.0) in unanesthetized precollicular-postmammilary decerebrate cats . During induced vocalization, the activities of both inspiratory (diaphragm) and expiratory (rectus abdominis) muscles were augumented. The stimulation also bilaterally augmented the activities of the abductor (posterior cricoarytenoid) and adductor (thyroarytenoid) muscles of the vocal folds during inspiration and expiration, respectively. The stimulation initiated in either inspiratory or expiratory phase reset the spontaneous respiratory rhythm . Following inspiration due to the activation of the diaphragm and abductor muscle of the vocal cords , expiration with vocalization and inspiration were alternately induced with a newly developed rhythm . This suggested that the tonic electrical stimulation delivered to the higher brainstem can alter rhythm generation of spontaneous respiration. Persistent opening of a T-tube inserted into the trachea decreased respiratory cycle . Although opening of the T-tube during vocalization decreased subglottic pressure , the expiratory phase did not abruptly terminated. It was suggested that the feedback input from the mechanoreceptors in the laryngeal mucosa was less important than the vagal feedback from the al veolar stretch receptors to maintain respiratory cycle during the induced vocalization .