The Response of the Vocal Folds to Electrical Stimulation of the Inferior Frontal Cortex of the Squirrel Monkey

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Abstract
Experiments were performed on squirrel monkeys to locate the cortical motor area of the vocal folds and to study their response to an electrical stimulus. The surface of the frontal gyri were electrically stimulated bilaterally, and the cortical area of the vocal folds established. A surgical procedure also was devised to record the mechanical properties of the thyroarytenoid muscle. The muscle was attached to a physiological transducer, and responses quantified by recording the output signal of the transducer on a high frequency inkwriter. The cortical motor area of the thyroarytenoid muscle was found to be in a subdivision of Brodmann's area 6. Bilateral contraction of the vocal folds was obtained by stimulation of either hemisphere; stronger responses were ipsilateral. With glottic closure, respiration ceased, and there was concomitant swallowing which appears to act as an auxiliary respiratory mechanism following asphyxia. Findings also were discussed in relation to phonation.