The effect of muscle vibration on short latency intracortical inhibition in humans

The purpose of the present study was to investigate the effect of muscle vibration (MV) on short latency intracortical inhibition (SICI) and facilitation (ICF) assessed by paired-pulse transcranial magnetic stimulation (TMS).

Nineteen right-handed healthy subjects were investigat ed without and with MV of the right extensor carpi radialis (ECR), using single- and paired-pulse TMS with interstimulus interval (ISI) of 3 and 13 ms. Intensities of the conditioning and test stimulus were 70 and 120 % of the motor threshold at rest. The motor-evoked potentials (MEPs) were recorded simultaneously from the vibrated ECR and its antagonist flexor carpi radialis (FCR).

In all the subjects a SICI of similar strength could be observed at 3 ms, at rest and during MV both in the vibrated muscle as well as in its antagonist. The subjects were divided in two groups according to the changes in MEP response to paired-pulse TMS with 13 ms ISI observed during MV. In nine subjects SICI was evident also at 13 ms when vibration was applied, while in another ten subjects vibration induced ICF at 13 ms.

The effect of MV is not just a facilitation of SICI, but a stronger prolongation of the effect of intracortical inhibition to an ISI at which ICF is well pronounced, when the intensity of the conditioning stimulus exceeds the threshold for intracortical facilitation.