Subthreshold low-frequency repetitive transcranial magnetic stimulation over the premotor cortex modulates writer's cramp

Abstract

Writer's cramp, or focal hand dystonia, is characterized by involuntary coactivation of antagonist or unnecessary muscles while writing or performing other tasks. Although the mechanism underlying this muscle overactivation is unknown, recent studies of changes in cerebral blood flow during writing have demonstrated a reduction in the activation of the primary motor cortex (MC) and hyperactivity of parts of the frontal non-primary motor areas. Therefore, any measures that decrease the activities of non-primary motor areas such as the premotor cortex (PMC) and the supplementary motor area (SMA) might improve dystonic symptoms. To explore this possibility, we studied nine patients with writer's cramp and seven age-matched control subjects, using subthreshold low-frequency (0.2 Hz) repetitive transcranial magnetic stimulation (rTMS), which exerts an inhibitory action on the cortex. Previous studies have demonstrated shortened cortical silent periods in dystonia, suggesting deficient cortical inhibition in the MC. We compared the silent periods and computer-assisted ratings of handwriting before and after rTMS applied to the MC, SMA or PMC. We also used the sham coil for control runs. Stimulation of the PMC but not the MC significantly improved the rating of handwriting (mean tracking error from the target, P = 0.004; pen pressure, P = 0.01) and prolonged the silent period (P = 0.02) in the patient group. rTMS over the other sites or using a sham coil in the patient group or trials in the control group revealed no physiological or clinical changes. This increased susceptibility of the PMC in dystonia suggests that the lack of inhibition in the MC is secondary to the hyperactivity of PMC neurons. Inhibition of the PMC using rTMS could provide a therapeutic measure of writer's cramp.

Impairment of Retention But Not Acquisition of a Visuomotor Skill Through Time-Dependent Disruption of Primary Motor Cortex

“…In addition, it might be argued that immediate-TMS caused a change in cortical excitability that affected the subsequent deadaptation period. Although this is already unlikely given the low frequency (ϳ0.2 Hz) and number of pulses (192) (Murase et al, 2005), it is ruled out by the result that the delayed-TMS group was not similarly affected by the TMS.…”

Transcranial magnetic brain stimulation modulates blepharospasm

“…Low-frequency subthreshold repetitive TMS has been well-documented to reduce cortical excitability noninvasively. 5,20 This study was performed to test whether rTMS compared to sham stimulation improves clinical symptoms and normalizes electrophysiologic characteristics in patients with BEB. We found significant improvements with the C-and the H-coils immediately after stimulation for all 3 outcome measures and 1 hour after stimulation in physician rating and patient rating.…”

“…Earlier studies reported suppressive effects on cortical excitability at frequencies as low as 0.2 and 0.3 Hz. 5,12 We applied rTMS with 0.2 Hz, 180 stimuli, 15 minutes per session, with a stimulator output of 100% active motor threshold, which was assessed at the tibialis anterior muscle with the circular coil for the C-coil and S-coil conditions and with the H-coil for the H-coil condition. rTMS was delivered to the ACC in each session.…”

Blepharospasm and the modulation of cortical excitability in primary and secondary motor areas

“…8 In a recent study, lfrTMS over primary and secondary motor areas in an inhibitory stimulation mode was used to modulate writer's cramp. 9 Stimulation of the PMC but not of the primary motor cortex (MC) improved tracking errors, pen pressure, and prolonged TMS-induced silent periods.…”