The Laryngeal and Speech Section investigates the control of laryngeal functioning in normal and disordered voice, speech and swallowing. The long-term goal of the Section is to identify the mechanisms involved in the pathogenesis of idiopathic speech and voice disorders. Disorders such as spasmodic dysphonia and stuttering are considered neurological disorders and involve involuntary disruptions in speech. Currently the Section is addressing: 1) the underlying mechanisms involved in normal and disordered laryngeal control for voice, speech and swallowing; 2) risk factors involved in familial laryngeal and speech disorders; and, 3) the use neuromuscular stimulation to provide integrative control of laryngeal function in voice, speech and swallowing. Significant advances made during the last year include the following. 1) Pathophysiology of Voice, Speech and Swallowing. Studies published this year were aimed understanding of the abnormalities underlying symptoms in dysphonia. One study examined laryngeal muscle physiology during voice onsets and offsets in untreated persons with Parkinson disease. In the non-medicated state, persons with higher levels of muscle activation had vocal fold bowing and greater impairment in voice onset and offset control for speech. Following administration of a therapeutic dosage of levodopa, those with reductions in thyroarytenoid muscle activity had greater improvements in voice onset and offset control for speech. The findings demonstrate hypophonia may be due to increased levels of laryngeal muscle activity interfering with voice onset and offset control for speech. We used an animal model to examine which types of afferents contribute to the elicitation of the laryngeal adductor reflex. A servomotor system provided the same displacement to move the arytenoid cartilage and stretch the thyroarytenoid muscle before and after a mucosal peel. Removal of the mucosa changed the frequency of early R1 responses from >92% to < 3 % occurrence. The results suggest that mucosal mechanoreceptors, rather than joint receptors or muscle spindles, may play a greater role in the elicitation of the laryngeal adductor response. In an effort to develop new treatment approaches for spasmodic dysphonia, we used an animal model to examine new methods for reducing the late R2 reflex, which is not suppressed in patients with spasmodic dysphonia in comparison with normal volunteers. We found that agents producing selective N-methyl-D-aspartate receptor blockade actively suppressed the occurrence of late R2 laryngeal adductor responses. One of these was dextromethorphan, a widely used antitussive agent. 2) Familial Laryngeal Disorders. Over the last 3 years the Section has been investigating familial vocal fold paralysis, a rare but life-threatening disease. Collaboration is ongoing with the Neurogenetics Branch to examine candidate genes after conducting a whole genome wide screen for a rare form of bulbar and spinal motor neuronopathy associated with vocal fold paralysis. 3) Development of a Laryngeal Neuroprosthesis for Voice and Swallowing. We recently published a study aimed at determining the degree of invariance in the pattern of laryngeal muscle activation in swallowing in normal volunteers when the gravitational forces on the bolus are changed from the upright to supine positions. Regardless of body position, the timing, amplitude, and duration of the thyroarytenoid muscles did not vary relative to the muscle activity onset in the submental muscle complex during swallowing. This suggests that same pattern of muscle stimulation onsets could be followed in attempting to aid patients with chronic dysphagia with aspiration. To develop a three dimensional model of the laryngeal cartilages, we used high resolution magnetic resolution imaging to extract the laryngeal cartilages and then register different larynges to the same 3-D space using the cricoid cartilage as the reference. We were successful in registering larynges of both males and females to the same 3-D space. This anatomical model will be used in future approaches to laryngeal dynamics for voice and airway protection control. To develop a neuromuscular stimulation prosthesis for persons with chronic dysphagia, we have recently demonstrated that with combined stimulation of the hyolaryngeal muscles in normal volunteers at rest, we could produce 50% of the normal laryngeal elevation and 80% of the normal movement velocity occurring during swallowing. These results suggest that stimulation of these muscles in dysphagic persons while they are attempting to swallow could assist in both the onset and extent of laryngeal elevation for the prevention of aspiration.
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