Reversal of the effects of focal suppression on pharyngeal corticobulbar tracts by chemesthesis coupled with repeated swallowing

Background Previous reports suggested the potential benefit of chemesthesis in the form of carbonated water (CW) integrated within dysphagia rehabilitation protocols. Here, we examined the effects of CW within a repeated swallowing protocol following focal suppression to pharyngeal cortical representation as a prelude to its application in dysphagic patients. Methods Fourteen healthy volunteers participated in a 3-arm study. Each participant underwent baseline corticobulbar pharyngeal and thenar motor-evoked potential (MEP) measurements with Transcranial Magnetic Stimulation (TMS). Subjects were then conditioned with 1Hz repetitive (r)TMS to induce focal unilateral suppression of the corticopharyngeal hotspot before randomization to each of three arms with 40 swallows of CW, non-CW and saliva swallowing on separate days. Corticobulbar and thenar MEPs were collected for up to 1 h and analyzed using repeated measures (rm)ANOVA. Results A 2-way rmANOVA for Intervention x Time showed a significant effect of Intervention (F-(1,F-13) = 7.519, p = 0.017) in both ipsi- and contra-lesional corticopharyngeal projections. Carbonation showed superiority in facilitating change by increasing pharyngeal cortical MEPs compared to non-CW (z = -3.05, p = 0.002) and saliva swallowing (z = -2.6, p = 0.008). No change in thenar representation (control) was observed nor in MEP latencies from both pharyngeal and thenar musculature. Conclusions We conclude that interventional paradigms with CW have the capacity to reverse the effects of a focal suppression with 1Hz rTMS more strongly than non-CW or saliva swallowing alone, producing site specific bi-hemispheric changes in corticopharyngeal excitability. Our data suggest that carbonation produces the effects through a mainly cortical mechanism.