Changes in the Excitability of Corticobulbar Projections Due to Intraoral Cooling with Ice.

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.