Motor Cortical Reorganization in Dysphagia Following Stroke

Swallowing is an essential part of life, whose central neural processing has increasingly been explored over the last 2 decades. Besides the well-known significance of medullary structures, involvement of a bilateral, widely distributed cortical and subcortical network has been shown. Moreover, the role of distinct brain areas could be related to specific aspects of swallowing control. Stroke is the most frequent reason for swallowing dysfunction. Dysphagia in stroke has a reported incidence of approximately 50% and is associated with increased mortality due to aspiration pneumonia. While 15% of patients suffer from persistent dysphagia, the majority shows fast recovery of swallow function within days to weeks. Thus, stroke constitutes a convenient lesion model to evaluate functional recovery due to spontaneous neuronal plasticity and following therapeutic interventions. The remarkable recovery of stroke-related dysphagia depends on compensatory reorganization in the undamaged hemisphere. The focus of treatment studies is therefore shifting from exercise-based manipulation of swallowing biomechanics towards approaches that modulate the underlying neural systems. By influencing cortical excitability and activity levels these methods are said to promote structural and functional reorganization resulting in clinical improvement. Techniques include those applied to the cortex like transcranial magnetic or direct current stimulation, but also those applied to the periphery, such as pharyngeal electrical stimulation. Some of these techniques have reached a stage of development that makes future use in clinical practice conceivable. Increasing the effect size and duration by further optimizing stimulation protocols will be a crucial issue.