Determination of the Resting Motor Threshold (RMT)

Each patient in the affected hemispheric group and unaffected hemispheric group was seated in a quiet environment and relaxed state. Electromyography (EMG) data representing oral swallowing musculature from mylohyoid muscles were detected using the same methods as Hamdy et al. (23). MagPro CCY-I stimulator (purchased from YIRUIDE Company, Wuhan, China) was used for magnetic stimulations with a 9 cm outer diameter figure-eight coil.

Cortical excitability on both hemispheres separately of each patient, including the motor evoked potential (MEP) and resting motor threshold (rMT) were measured using single-pulse TMS. The coil was moved around in an area within 2–4 cm anteriorly and 4–6 cm laterally of the vertex of the cranium to locate the mylohyoid cortical region of the hemisphere to obtain the maximum MEP recording (23). The maximum MEP recording location was regarded as the “hot spot,” representing magnetic stimulation delivered to the area. Single-pulse TMS was then delivered to the “hot spot” with a 2% reduction in the output of the stimulator. The definition of the rMT is that in 10 consecutive trials of mylohyoid muscles, five trials can induce the minimum stimulus intensity of MEP > 50 μV. The “hot spot” was defined as an unaffected symmetrical hemisphere if MEPs were absent when the stroke-affected hemisphere was stimulated.

In previous studies, it has been identified that rTMS stimulation is effective regardless of which side of the cerebellum is stimulated (19, 24). For the cerebellum group, the coil was fixed at the mylohyoid cortical representation of the cerebellum (4.3 cm to lateral and 2.4 cm below the inion) (19). The rMT was determined by the rMT of the mylohyoid cortical area of the unaffected hemisphere.