Absence of Modulation in Interhemispheric Inhibition During Sustained Muscle Contraction as Measured by Ipsilateral...

Interhemispheric inhibition (IHI) can be assessed using transcranial magnetic stimulation (TMS). The ipsilateral silent period (ISP), which represents IHI from the primary motor areas (M1) on the TMS stimulation side to the M1 on the opposite side of the TMS stimulation, is elicited. The variability in ISP associated with changes in contraction intensity at 30% and 50% of maximum voluntary contraction (MVC) and the muscle of the contralateral limb remains unclear.

This study investigated the influence of these variables on ISPs. We performed electromyography monitoring for ISP and evaluated motor evoked potentials (MEPs) and contraction force during motor tasks in 15 right-handed healthy adults. Measurements involved the bilateral first dorsal interosseous and the right biceps brachii muscles. After identifying the optimal TMS target (hot spot) and establishing the resting motor threshold, 20 TMS pulses were applied in each condition.

There was no interaction or main effect on ISP duration under any condition, while MEP displayed significant interaction and main effects for contraction intensity and muscle type. We found no variations in ISP across motor tasks in this study.

We observed no ISP alterations despite changes in M1 excitability, suggesting that other brain regions, such as the supplementary motor area (SMA), may modulate IHI.