Exploring the effects of synchronous pharyngeal electrical stimulation with swallowing carbonated water on cortical excitability in the human pharyngeal motor system

Abstract

Key Points• Excitation of human pharyngeal motor cortex can be induced by pharyngeal electrical stimulation (PES) and swallowing carbonated water (CW). This study was undertaken to investigate the effect of synchronously combining PES with swallowing CW.• Pharyngeal cortical and brainstem excitation was investigated using transcranial or transcutaneous magnetic stimulation (TMS).• PES was most effective at inducing excitation in the pharyngeal motor cortex. Combination of PES and CW were less effective in producing cortical excitability but induced transient excitation in the brainstem. Our data indicate the PES may be more advantageous than combined swallowing stimuli for driving cortical changes in the swallowing system which may be useful in dysphagia rehabilitation. AbstractBackground Previous reports have revealed that excitation of human pharyngeal motor cortex can be induced by pharyngeal electrical stimulation (PES) and swallowing carbonated water (CW). This study investigated whether combining PES with swallowing (of still water, SW or CW) can potentiate this excitation in either cortical and/or brain stem areas assessed with transcranial and transcutaneous magnetic stimulation (TMS). Methods Fourteen healthy volunteers participated and were intubated with an intraluminal catheter to record pharyngeal electromyography and deliver PES. Each participant underwent baseline corticopharyngeal, hand and craniobulbar motor-evoked potential (MEP) measurements. Subjects were then randomized to receive each of four 10-min interventions (PES only, Sham-PES+CW, PES+CW, and PES+SW). Corticobulbar, craniobulbar and hand MEPs were then remeasured for up to 60 min and data analyzed using ANOVA and post hoc t-tests. Key Results A two-way rmANOVA for Interventions 9 Time-point showed a significant corticopharyngeal interaction (p = 0.010). One-way ANOVA with post hoc t-tests indicated significant cortical changes with PES only at 45 (p = 0.038) and 60 min (p = 0.023) and ShamPES+CW immediately (p = 0.008) but not with PES+CW or PES+SW. By contrast, there were immediate craniobulbar amplitude changes only with PES+CW (p = 0.020) which were not sustained. Conclusions & Inferences We conclude that only PES produced long-term changes in corticopharyngeal excitability whereas combination stimuli were less effective. Our data suggest that PES alone rather than in combination, may be better for the patients who have difficulty in performing voluntary swallows.

TMS brain mapping of the pharyngeal cortical representation in healthy subjects

“…Also, participant population being more homogeneous than those used in previous studies might be another underlying reason, but we not yet have concrete evidence about it. Despite our reported cortical representation being more lateral and posterior to previous works, the map locations are generally consistent with previous studies in the literature [9,11,20,43].…”

“…It is therefore also difficult to record electromyographic (EMG) activity of the pharyngeal muscles as their activation can be relatively weak. Nevertheless, intra-pharyngeal EMG catheters have made recording muscle activity easier and have been utilized in various studies and even in clinical practice [19,20]. These catheters house a pair of bipolar platinum ring electrodes and that are spaced 0.1 cm apart, which can precisely record the different anatomic parts of esophagus of interest.…”

Cold thermal oral stimulation produces immediate excitability in human pharyngeal motor cortex

“…The resting motor threshold (rMT) was identified at this site using single pulses of stimulation to achieve PMEPs greater than 20 μV in at least 5 of 10 trials. The pharyngeal motor cortex which produced the larger amplitude of PMEPs at the lowest threshold was defined as the stronger pharyngeal hemisphere and the contralateral side was determined as weaker pharyngeal hemisphere…”

“…The resting motor threshold (rMT) was identified at this site using single pulses of stimulation to achieve PMEPs greater than 20 μV in at least 5 of 10 trials. The pharyngeal motor cortex which produced the larger amplitude of PMEPs at the lowest threshold was defined as the stronger pharyngeal hemisphere and the contralateral side was determined as weaker pharyngeal hemisphere 26,27 The rMT for the APB muscle, generating the corticospinal thenar responses, was measured at hand motor area adjacent to stronger pharyngeal hemisphere using single pulses of TMS to induce TMEPs responses greater than 100 μV in at least 5 of 10 consecutive stimulations.…”

The BDNF polymorphism Val66Met may be predictive of swallowing improvement post pharyngeal electrical stimulation in dysphagic stroke patients

“…Pharyngeal electrical stimulation (PES) has been found to show plausible promise as a potential treatment for dysphagic stroke in both proof of concept (phase 1) and randomized control trials . The mechanism of PES is believed to be an enhancement of the cortical areas within the pharyngeal motor cortex leading to improved swallowing function …”