Laryngeal adaptation in speech and swallowing

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Project Summary The overall goal of this proposal is to examine feed-forward laryngeal adaptation in speech and swallowing. Over several decades, the research literature on laryngeal function in speech and swallowing has primarily assumed that sensory feedback drives laryngeal modulation to maintain adequate laryngeal function. In feedback control, sensory input can be used to adjust ongoing movements. In feed-forward control, however, input from previously completed movements are used to predict, plan and execute future movements that have not yet occurred. We posit that a feed-forward paradigm deserves more attention and might be more effective in rehabilitation programs because many aspects of speech and swallowing are inherently under feed-forward control. This is because feedback modifications may not be possible in (a) swallowing laryngeal movements that are ballistic or in (b) very short speech sounds or early voicing periods. We hypothesize that laryngeal function in healthy adults is remarkably accurate in speech and swallowing because errors can be avoided before they occur due to feed-forward control. However, in individuals with neurogenic dysarthria and dysphagia, we hypothesize that continued dysfunction could be due to impaired laryngeal feed-forward adaptation. We will test this hypothesis with 2 Aims. Aim 1 is to differentiate feed-forward laryngeal adaptation among cerebral stroke, spinocerebellar ataxia type 6 (SCA6), and healthy controls when (1A) speech is perturbed with respiratory loading to restrict vocal loudness and (1B) swallowing is perturbed with neck electrical stimulation to restrict laryngeal elevation. Aim 2 is to examine whether laryngeal adaptation outcomes in patients with cerebral stroke and ataxia correlate with dysphagia and/or dysarthria severity over a period of one year. Our preliminary data suggest that feed-forward laryngeal adaptation is fine-tuned in healthy adults. This is characterized by adaptation of only laryngeal functions that are essential to overcoming the perturbation, while other non-essential laryngeal functions remain stable. Conversely, patients with cerebral stroke and SCA6 do not have fine-tuned laryngeal adaptation. Instead, extraneous movements during the perturbation might be interfering with ongoing error-reduction processes. These two patient groups offer a unique opportunity to examine the differential effects of cerebral versus cerebellar contributions to laryngeal adaptation and control in naturally occurring human models of disease. This grant is the first step in our long- term goal to establish that speech and swallowing rehabilitation might be more effective if feed-forward control principles are incorporated. The scientific rigor of this study and the strength of the team assure that outcomes will impact future directions of sensory-motor adaptation across several other systems of the body.