"Virtual" lesioning of the human oropharyngeal motor cortex: a videofluoroscopic study

Abstract

Objective: To use focal cortical inhibition and create a "virtual" lesion in the oropharyngeal motor cortex in healthy subjects to determine whether this provokes swallowing dysfunction.

Design: Intervention study: before and after cortical stimulation.

Setting: Tertiary care center.

Participants: Healthy adult volunteers (N=9; age range, 21-44y) participated in the study.

Interventions: Active or sham 1-Hz repetitive transcranial magnetic stimulation (rTMS) over the cortical sites in each hemisphere evoking the largest mylohyoid motor-evoked potentials (mMEPs) to single pulse transcranial magnetic stimulation.

Main outcome measures: Videofluoroscopic assessment was performed before and 5, 30, and 60 minutes after rTMS.

Results: The motor threshold was 83%±10% for the hemisphere with the larger mMEP (dominant) and 92%±9% for the hemisphere with the smaller mMEP (nondominant). When rTMS was performed over the dominant hemisphere, there was a decrease in oral transit time (P=.05), an increase in swallow reaction time (P=.0001), but no change of pharyngeal transit time or laryngeal closure duration. When rTMS was performed on the nondominant hemisphere, there was also a decrease in oral transit time (P=.05), but no change in any of the other swallowing measures. Neither active intervention produced any signs of aspiration or penetration. Sham stimulation had no effect.

Conclusions: Inhibiting the human oropharyngeal motor cortex using rTMS transiently modifies swallowing behavior in a way reminiscent to that seen in stroke patients.