A Pilot Investigation of Triggering Methods for Motor Evoked Potentials of the Submental Muscle Group

Purpose: Prior research has utilized analysis of motor evoked potentials (MEP) to infer treatment effects on neural pathways underlying swallowing. These MEPs were recorded at pharyngeal and anterior hyomandibular (submental) muscles at rest. This pilot study evaluated whether contraction of floor of mouth muscles during three different tasks influenced the amplitude of MEPs evoked in these muscles. Method(s): MEPs were recorded from15 healthy volunteers during execution of three tasks (volitional floor-of-mouth contraction, volitional swallowing and reflexive swallowing). Single pulse transcranial magnetic stimulation (Magstim 200, Magstim Company Limited, Whitland, Wales) was triggered when floor of mouth EMG amplitude reached a threshold of 70% average swallowing amplitude. 15 MEPs were recorded for each subject in each condition and subjected to RMANOVA analysis. Results: In 6 of 15subjects, identifiable MEPs could only be detected during volitional contraction; in 2/11 subjects, MEPs could be recorded in the volitional contraction and volitional swallowing tasks and in 7/11 participants, MEPs could be recorded in all three tasks. Grouped RM ANOVA on the 9 subjects that displayed MEPs in the volitional conditions revealed no significant differences between amplitudes (F = .671, p = .437] or onset latencies [F = 3.159,p = .113]. In the 7/11 subjects that displayed MEPs in all three tasks, no significant differences were found between amplitudes [F = .074,p = .929] or onset latencies [F = 3.584, p = .060].Conclusions: These preliminary data suggest differences in cortical drive between volitional contraction, volitional swallowing and reflexive swallowing. Therefore methods should be considered in future research investigating swallowing related MEPs.