Exploring parameters of gamma transcranial alternating current stimulation (tACS) and full-spectrum transcranial random noise stimulation (tRNS) on human pharyngeal cortical excitability

New and Evolving Treatments for Neurologic Dysphagia

Despite swallowing being a frequently performed daily function, it is highly complex. For a safe swallow to occur, muscles within the head, neck, and thorax need to contract in a concerted pattern, controlled by several swallowing centers at multiple levels of the central nervous system, including the midbrain, cerebral cortex, and cerebellum in addition to five cranial nerves. Dysphagia, or difficulty swallowing, is caused by a long list of pathologic processes and diseases, which can interfere with various stages along the swallowing sensorimotor pathway. When present, dysphagia leads to increased mortality, morbidity, hospital length of stay, and reduced quality of life. Current dysphagia management approaches, such as altering the texture and consistency of foods and fluids and teaching patients rehabilitative exercises, have been broadly unchanged for many years and, in the case of texture modification, are of uncertain effectiveness. However, evidence is emerging in support of new medication-based and neuromodulatory treatment approaches. Regarding medication-based therapies, most research has focused on capsaicinoids, which studies have shown are able to improve swallowing in patients with post-stroke dysphagia. Separately, albeit convergently, in the field of neuromodulation, there is a growing and positive evidential base behind three non-invasive brain stimulation techniques: repetitive transcranial magnetic stimulation (rTMS), transcranial direct current stimulation (TDCS), and pharyngeal electrical stimulation (PES). Should some or all of these emerging therapies fulfill their promise, dysphagia-related patient outcomes may be improved. This paper describes the current state of our understanding regarding new medication and neuromodulation-based neurogenic oropharyngeal dysphagia treatments.

The neurorehabilitation of post-stroke dysphagia: Physiology and pathophysiology

Swallowing is a complex process involving the precise contractions of numerous muscles of the head and neck, which act to process and shepherd ingested material from the oral cavity to its eventual destination, the stomach. Over the past five decades, information from animal and human studies has laid bare the complex network of neurones in the brainstem, cortex and cerebellum that are responsible for orchestrating each normal swallow. Amidst this complexity, problems can and often do occur that result in dysphagia, defined as impaired or disordered swallowing. Dysphagia is common, arising from multiple varied disease processes that can affect any of the neuromuscular structures involved in swallowing. Post-stroke dysphagia (PSD) remains the most prevalent and most commonly studied form of dysphagia and, as such, provides an important disease model to assess dysphagia physiology and pathophysiology. In this review, we explore the complex neuroanatomical processes that occur during normal swallowing and PSD. This includes how strokes cause dysphagia, the mechanisms through which natural neuroplastic recovery occurs, current treatments for patients with persistent dysphagia and emerging neuromodulatory treatments.

Evaluating the Therapeutic Application of Neuromodulation in the Human Swallowing System

In the last two decades, the focus of neurogenic dysphagia management has moved from passive compensatory strategies to evidence-based rehabilitative approaches. Advances in technology have enabled the development of novel treatment approaches such as neuromodulation techniques, which target the promotion of neurological reorganization for functional recovery of swallowing. Given the rapid pace of development in the field, this review aims to summarize the current findings on the effects of neuromodulation techniques on the human swallowing system and evaluate their therapeutic potential for neurogenic dysphagia. Implications for future clinical research and practical considerations for using neuromodulation in clinical practice will also be discussed.