Strength training and repetition of motor activity alone is not thought to result in functional recovery where impaired motor performance is the baseline. We know this to be true in movements required for both speech and swallowing in our patients who experience ataxia, apraxia, and other motor disruptions. Encouraging a patient with dysphagia to simply “practice” a dysphagic swallow with no modification to this task, is unlikely to produce a desired effect (Huckabee & McCrae, 2014).
Here is where motor learning, the field of study that aims to clarify how motor performance improves and is subsequently retained, becomes imperative to our practice as speech-language pathologists. A crucial component in motor learning is motor adaptation, the short-term process of reducing errors in a sensory-motor task. This involves the brain’s prediction and subsequent evaluation of an executed motor plan.
Humbert & German (2013) conducted a study investigating the effects of repeated swallowing of the same liquid bolus on hyoid bone and laryngeal kinematics (the motions of structures involved in swallowing). The bolus was delivered either to the oral cavity or directly to the pharyngeal cavity. It was noted the oral cavity plays a crucial role in providing a motor plan for hyolaryngeal movements, as these kinematics responded to bolus volume differences only with oral delivery. This highlights the importance of oral sensory-motor integration for kinematics of the components in the pharyngeal swallow.
Additionally, feedback is a key element in motor learning regarding task performance. Patients with neurological impairment are more likely to have disrupted intrinsic feedback. As swallowing produces no visual external movement patterns, these patients are less likely to learn through repetition and therefore augmented feedback may be necessary for them to understand movement accuracy and performance (Huckabee & McCrae, 2014). Two types of pertinent feedback important to motor learning are knowledge of performance (KP) and knowledge of results (KR). KP is defined as information regarding movement execution and KR is defined as information regarding the movement outcome (Gentile, 1972; Adams, 1971).
A common tool for training rehabilitation strategies in dysphagia management that integrates this concept of feedback involves the use of surface electromyography (sEMG). Galek & Bice (2020) demonstrates the significance that sEMG visual and clinician verbal feedback play for increasing “swallow effort ratio” (SER) between execution of typical and effortful swallows. Participants in the group who received visual and verbal feedback were provided KP with instructions such as “push your tongue against the roof of your mouth, and squeeze hard when you swallow”, and KR via sEMG display of noting whether or not they achieved the set target of an effortful swallow. The other participant group did not receive visual or verbal feedback. The results showed a significant difference in peak amplitude with a greater mean SER for the visual and verbal feedback group.
Other recent research suggests great benefit in the use of sEMG for increasing skill and precision of movement using a targeted, skill-based rehabilitation protocol. This approach requires repeated execution of skilled swallowing movements, progressively challenging targets for timing and degree of muscle contraction, and ongoing and delayed feedback regarding task performance. In the face of injury or disease, relearning or modifying the complex sequence of events involved in swallowing poses a much greater challenge (Huckabee & McCrae, 2014). Although further research is needed in the field of motor learning as it relates to deglutition, the data presented here, in conjunction with decades of motor learning literature in various fields of study, are compelling in understanding its importance for use in speech and swallowing rehabilitation approaches.
References:
Adams J. A. (1971). A closed-loop theory of motor learning. Journal of motor behavior, 3(2), 111–149. https://doi.org/10.1080/00222895.1971.10734898
Galek, K. E., & Bice, E. M. (2020). The Influence of Surface Electromyography Visual and Clinician Verbal Feedback on Swallow Effort Ratio at Different
Bolus Volumes in a Healthy Population. Folia Phoniatrica et Logopaedica (IALP), 1–6. https://doi.org/10.1159/000511497.
Gentile, A. (1972). A Working Model of Skill Acquisition with Application to Teaching. Psychology. https://doi.org/10.1080/00336297.1972.10519717.
Huckabee, M. L., & Macrae, P. (2014). Rethinking rehab: Skill-based training for swallowing impairment. SIG 13 Perspectives on Swallowing and
Swallowing Disorders. Dysphagia, 23(1), 46-53. https://doi.org/10.1044/sasd23.1.46
Humbert, I. A., & German, R. Z. (2013). New directions for understanding neural control in swallowing: the potential and promise of motor learning.
Dysphagia, 28(1), 1-10. https://doi.org/10.1007/s00455-012-9432-y