Dysphagia, or disordered swallowing, is prevalent in almost all neurodegenerative conditions and results in the inability to effectively protect the lower airways from foreign (i.e., food/liquid) and endogenous (i.e., saliva) material \[1-3\]. An unfortunate consequence of dysphagia is aspiration pneumonia, which is a leading cause of death in Parkinson's disease (PD) \[4-6\]. Swallowing therapy has proven to be effective for the management of dysphagic symptoms in PD. Treatment is most often delivered in clinics once/week over short time periods with the expectation that exercises be completed at-home. However, these paradigms lack biofeedback to assess the accuracy and strength of the prescribed exercise and accountability to ensure completion of the exercise program. Without biofeedback or options for long-term therapeutic intervention at-home, patients often regress to baseline levels \[7-9\]. The proposed research project seeks to test the effectiveness of a novel at-home surface electromyography (sEMG) biofeedback therapy tool called Biofeedback in Strength and Skill Training (BiSSKit) on swallowing safety and efficiency in patients with PD. The significance of this project lies in the fact that dysphagia is expensive in terms of patient quality of life, health outcomes, and healthcare costs \[10, 11\] often increasing hospital costs by approximately 40% \[12\]. Thus, a targeted swallowing therapy system with biofeedback that can be utilized at-home may reduce hospitalizations secondary to dysphagia, help maintain therapeutic gains, and reduce the burden that dysphagia places on our healthcare system.

sEMG is a therapy tool that has been used in rehabilitation practice for decades. Use of sEMG during swallowing therapy involves placement of electrodes under the chin (overlying the anterior belly of the digastric, mylohyoid and geniohyoid muscles) \[13\]. While the patient completes a swallowing task, electrodes detect collective muscle contractions associated with hyolaryngeal excursion - a biomechanical event critically important to airway safety and swallowing efficiency \[14\]. The patient can then see the waveform of the swallow displayed on a computer monitor. Measures of swallowing "strength" are derived from the amplitude of the waveform. sEMG hardware and associated software available in the marketplace today is cost prohibitive and thus, in the United States, only available for office-based swallowing intervention.

sEMG provides external biofeedback regarding swallowing parameters by activating neural networks controlling both motor execution and imagery of the act of swallowing including the pre- and postcentral gyrus, inferior frontal gyrus, basal ganglia, insula, and cerebellum \[15\]. Research has shown that exercise programs incorporating biofeedback promote significant physiologic change that is maintained over time in patients with dysphagia \[14, 16-18\]. Patients with PD benefit greatly from biofeedback exercises for respiratory muscle strength and lingual strengthening programs and have even been found to maintain the gains made in therapy with at-home programs \[7, 16, 19\].

A limitation of the currently available sEMG programs is that research studies have solely focus on the strength aspects of the swallowing (amplitude of the waveform) while failing to address the dynamic, skill-based parameters such as timing and volitional initiation that is captured in waveform morphology. Skill based swallowing training focuses on the precision of movements; and this is especially important for patients with PD \[14\]. Additionally, traditional sEMG systems in the US lack the ability for clinicians to modulate swallowing targets during tasks, which, according to principles of neuroplasticity, is essential for maximizing therapeutic results. The BiSSKit program is a well-researched office-based biofeedback system that adheres to principles of neuroplasticity and incorporates skill training in addition to strength training \[14\]. Developed in New Zealand and recently approved by the US FDA, this program has been converted into an affordable and accessible home-based application for tablet computers. This hybrid BiSSKiT system incorporates clinical visits and home-based skill/strength training and shows promise to change current therapy delivery models. Although exciting, there is a paucity of data regarding the use of the BiSSKiT with daily home therapy focused on strength and skill based swallowing training on changes to swallowing safety and efficiency in people with PD. This study seeks to evaluate the impact of this device on swallowing outcomes compared to traditional swallowing therapy models in PD.