Cerebellar Transcranial Magnetic Stimulation Reduces the Silent Period on Hand Muscle Electromyography During Force Control

Abstract

This study aimed to investigate whether cerebellar transcranial magnetic stimulation (C-TMS) affected the cortical silent period (cSP) induced by TMS over the primary motor cortex (M1) and the effect of interstimulus interval (ISI) on cerebellar conditioning and TMS to the left M1 (M1-TMS). Fourteen healthy adult participants were instructed to control the abduction force of the right index finger to 20% of the maximum voluntary contraction. M1-TMS was delivered during this to induce cSP on electromyograph of the right first dorsal interosseous muscle. TMS over the right cerebellum (C-TMS) was conducted prior to M1-TMS. In the first experiment, M1-TMS intensity was set to 1 or 1.3 × resting motor threshold (rMT) with 20-ms ISI. In the second experiment, the intensity was set to 1 × rMT with ISI of 0, 10, 20, 30, 40, 50, 60, 70, or 80 ms, and no-C-TMS trials were inserted. In results, cSP was significantly shorter in 1 × rMT condition than in 1.3 × rMT by C-TMS, and cSP was significantly shorter for ISI of 20–40 ms than for the no-C-TMS condition. Further, motor evoked potential for ISI40-60 ms were significantly reduced than that for ISI0. Thus, C-TMS may reduce cSP induced by M1-TMS with ISI of 20–40 ms.

Frequency-dependent modulation of cerebellar excitability during the application of non-invasive alternating current stimulation

“…Additionally, one could implement a combination of TMS and electroencephalogram (EEG) to assess excitability and connectivity following cerebellar tACS [36]. Finally, given the interactions between cerebellar activity and cortical GABA-b inhibitory activity [10,55], future studies should also consider evaluating whether tACS is capable of modulating long intracortical inhibition and cortical silent period.…”

Excessive excitability of inhibitory cortical circuit and disturbance of ballistic targeting movement in degenerative cerebellar ataxia

“…For instance, in motor-stopping tasks, the longer the cSP during 10% MVC, the better the task performance 22 . Additionally, cSP at 100% MVC is shorter than at 10% MVC 23 , 42 . In other words, when producing strong force, intracortical inhibition is flexibly released, contributing to increased excitability of the corticospinal tract.…”

“…Factors related to cSP include age 40 and stimulus intensity 23 , 34 . Therefore, age-matched healthy participants were selected as the target group in this study.…”

“…Therefore, two independent assessors measured the cSP, and the average of the two cSP values was used for subsequent analyses. The independent assessors were selected based on their experience in the previous analysis 23 .…”

“…Healthy subjects with longer cSP have been reported to perform better on motor cancellation tasks 22 . Furthermore, cSP is modulated by conditioning with cerebellar single-pulse TMS, indicating that the cerebellum has an output to the GABA-mediated inhibitory circuit in M1 23 . Individuals with DCA have impaired force control 24 .…”