The aim of this study was to assess the effects of ice applied to the oral cavity on the excitability of corticobulbar projections to the swallowing muscles. The subjects were 8 healthy adult volunteers (mean age 29.0 ± 4.9 years). Motor-evoked potentials (MEPs) were recorded from the suprahyoid muscle complex using surface electrodes. Two blocks of 20 MEPs with a test stimulus intensity of 120% of the resting motor threshold were recorded at rest (baseline). Subjects then underwent 5-min thermal stimulation by either of 3 different types: (1) “ice-stick inside mouth,” (2) “ice-stick on neck,” and (3) “room temperature inside mouth.” Blocks of 20 MEPs were then recorded immediately and at 5-min intervals for the following 15 min. There was a significant difference in the effects of the 3 interventions on the amplitude of the MEPs following stimulation (two-way ANOVA: INTERVENTION × TIME; F8,84 = 3.76, p < 0.01). One-way ANOVA was used to evaluate the changes over time for each intervention type. Only “ice-stick inside mouth” caused an increase in the MEPs (one-way ANOVA main effect of TIME: F4,28 = 4.04, p = 0.010) with significant differences between baseline and P10 (mean difference 0.050; confidence interval (CI) 95% 0.019–0.079; p = 0.004). There were no significant effects of either “ice-stick on neck” or “room temperature inside mouth” (F4,28 = 1.13, p = 0.36; F4,28 = 1.36, p = 0.27, respectively). Ice stimulation within the oral cavity increases the excitability of the cortical swallowing motor pathway.
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