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 factors and mechanisms involved in the pathogenesis of two idiopathic speech and voice disorders, spasmodic dysphonia and stuttering. Both 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 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 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 at improved understanding of the abnormalities underlying symptoms in abductor spasmodic dysphonia. It has long been assumed that voice breaks in this disorder are secondary to spasmodic bursts in the posterior cricoarytenoid muscle. A cross-over study evaluated the effects of endoscopic and percutaneous botulinum toxin injections into the posterior cricoarytenoid muscle on symptoms. Blinded counts of symptom frequency were conducted before and after each treatment. No significant reductions in symptoms were found with either injection type, although the expected reductions in movement occurred. The results differed from previous unblinded studies and suggested that symptom generation may involve other control abnormalities in this disorder. In subsequent study we compared activity in multiple intrinsic laryngeal muscles on both side of the larynx during symptom generation with normal speakers. We found that patients with abductor spasmodic dysphonia had asymmetries in thyroarytenoid and cricothyroid activation between the right and left sides of the larynx. Some patients had higher levels of muscle activation on the right side. The results suggest that these patients may have unilateral muscle tone abnormalities similar to those found on both sides of the larynx in patients with adductor spasmodic dysphonia. A further investigation of this hypothesis is now underway. 2) Familial Laryngeal Disorders. Over the last 3 years the Section has been investigating familial vocal fold paralysis, a rare but life-threatening disease. Detailed examinations of the different phenotypes indicate various disease types can be involved: some are isolated to motor control of the larynx and diaphragm; others are a polyneuropathy affecting both motor and sensory axons; while another form may involve both spinal and brain stem motor neurons. Collaboration with the Neurogenetics Branch is ongoing to examine candidate genes as well as conducting a whole genome wide screen. 3) Development of a Laryngeal Neuroprosthesis for Voice and Swallowing. Reduced extent and abnormal timing of laryngeal elevation occur in patients at risk for aspiration following stroke. We determined whether extrinsic laryngeal muscle stimulation could be used to elevate the larynx in humans. Combined stimulation of the thyrohyoid and mylohyoid muscles produced fifty percent of the laryngeal elevation that occurs during normal swallowing. Obstructive sleep apnea can be due to collapse of the tongue into the pharynx. We examined whether stimulation of the geniohyoid might bring the base of the tongue forward to produce pharyngeal opening. Measurement of nasoendoscopic recordings was used to quantify the diameter before and during geniohyoid stimulation. Rapid and sustained pharynx widening occurred with 30 Hz stimulation, demonstrating a potential new method for management of this common life-threatening disorder.
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