The precisely controlled use of the laryngeal muscles is essential to all aspects of oral communication. Our current knowledge of the neural mechanisms of laryngeal control is extremely limited, however, and much of what is known about laryngeal motoneurons is related to their involvement with respiratory actions and protective reflexes. These are important actions, but it will be impossible to understand the role of the larynx in speech without also studying phonation. The lack of detailed information concerning the production and control of phonation is an unfortunate situation because human communication problems such as spasmodic dysphonia, stuttering, dysprosody, some vocal pathologies, and swallowing problems are related, in some degree, to abnormalities of laryngeal control. The broad, long-range goal of the proposed research is to develop a sustained program of basic research on 1) the behavior of laryngeal motoneurons associated with phonation, 2) the sensory signals that come back to the nervous system from the larynx during phonation, 3) the descending neural pathways that come from the cerebral cortex to initiate and control this process, and 4) the motor and sensory nerves that innervate the larynx. The central approach to these goals is to take advantage of the fat that fully-anesthetized animals, in particular dogs, can be made to produce sustained phonation by electrical stimulation of regions of the midbrain. The dog is an appropriate species for these studies because it has been used extensively in development of mathematical models of vocal fold vibration, and in otolaryngology research, and it is a species in which it has been demonstrated that midbrain stimulation can be manipulated to produce phonation at different pitches. A second major goal of the research is to use this animal model of phonation to study applied questions such as the mechanisms of botulinum toxin's ability to ameliorate the condition of spasmodic dysphonia, and how environmental and pharmacological factors influence the ability of the voice to be damaged by overuse. The dog phonation preparation will also be used to refine and extend biomechanical model of vocal fold vibration.
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