# Bioelectrical Signals for the Diagnosis and Therapy of Functional Gastrointestinal Disorders
## 2 Oropharynx and Esophagus
### Therapies  
Historically, pharyngeal swallowing was considered to be largely a medullary driven reflex [35; 36; 37]. Early research by [PERSON] et al. in 1988 expanded on this view by describing swallowing as a patterned response, regulated and upheld by complex neurophysiological processes [38]. Increased precision in neuroimaging techniques has led to further models of swallowing motor control that suggest a significant contribution of the cerebral cortex in modulating the pharyngeal response [39; 40]. These advances in neurophysiology along with the role of neuroplasticity in adaptive swallowing behavior have led to a shift in dysphagia therapy from compensation to the recovery of swallowingfunction. Early approaches to rehabilitation focused on direct changes to muscle recruitment with peripheral strengthening approaches. More recently, rehabilitation approaches have expanded to highlight engagement of cortical regions in the control of motor programming for swallowing [41], employing principles of neural adaptation to rehabilitation approaches [15].  
The use of motor imagery of swallowing for dysphagia rehabilitation was first investigated using EEG [42]. Human-computer interfaces have since been created to allow patients to visualize their swallowing function in real time. These interfaces used EEG or MEG to support neurofeedback for sensory activation and EMG, or other measures of swallowing biomechanics, to provide biofeedback for adaptation of peripheral muscle activation [43]. These functional feedback therapeutic techniques increase swallowing muscle strength, correct biomechanical sequencing of swallowing structures and may promote neural plastic changes to reform swallowing neural circuitry pathways [44; 45].  
Stimulation of the orophynx and esophagus is challenging due to lack of rhythmic myoelectrical activity and the complexity of biomechanical movements, particularly in the pharynx. Stimulation strategies include pharyngeal electrical stimulation (PES) and neuromuscular electrical stimulation (NMES). A study which performed PES on post-stroke dysphagia patients showed improvements in the sequencing of swallowing events and reduced aspiration [46], while a more recent PES study reported no improvement in dysphagia [47]. An NMES stimulation device for treatment of pharyngeal dysphagia called Vitalstim Plus (DJO Global Inc, Vista, CA, USA) is commercially available. However, the reported outcomes of NMES in the treatment of dysphagia are inconsistent and often contradicting [48; 49]. Central nervous system stimulation strategies include transcranial magnetic stimulation and transcranial direct current stimulation [50; 51]. A meta-analysis on central nervous system stimulation strategies concluded that no significant improvements in dysphagia were found with the application of direct current stimulation, while subgroup analysis showed a significant improvement in dysphagia when high-frequency magnetic stimulation was applied over contralesional hemispheres [50]. However, a subsequent meta-analysis that controlled for stimulation hemisphere demonstrated that transcranial direct current stimulation resulted in a more robust clinical effect than transcranial magnetic stimulation studies [51].