Effects on the right motor hand‐area excitability produced by low‐frequency rTMS over human contralateral homologous cortex

Abstract

Repetitive transcranial magnetic stimulation (rTMS) has long lasting effects on cortical excitability at the site of stimulation, on interconnected sites at a distance and on the connections between them. In the present experiments we have used the technique of transcallosal inhibition between the motor cortices to examine all three effects in the same protocol. Ten healthy subjects received 900 rTMS stimuli at 1 Hz from a figure of eight coil over the left motor hand area. The intensity of rTMS was above the threshold for inducing short latency interhemispherical inhibition with a single stimulus (equivalent to 115–120 % resting motor threshold). Before and after the rTMS we evaluated: (1) in the left hemisphere, the amplitude of motor‐evoked potentials (MEPs), and contralateral and ipsilateral cortical silent periods (CSP, ISP); (2) in the right hemisphere, MEP, CSP, ISP and short‐interval intracortical inhibition and intracortical facilitation (SICI/ICF), and (3) interhemispherical inhibition (IHI) from the left‐to‐right hemisphere using a paired‐pulse method. There were two main effects after rTMS to the left hemisphere: first, the amplitude of MEPs from the right hemisphere increased; second, there was a reduction in the IHI from the left‐to‐right hemisphere at interstimulus intervals of 7 and 10 ms but not at longer intervals (15–75 ms). Control experiments showed that these effects were not due to afferent inputs produced by the muscle twitches induced during the rTMS. The data are compatible with the notion that rTMS to the left hemisphere leads to reduced interhemispherical inhibition of the right hemisphere and a consequent increase in corticospinal excitability in that hemisphere.

Neurophysiological Mechanisms Involved in Transfer of Procedural Knowledge

“…These results are in agreement with previous studies showing that, at a larger size of a test MEP, the magnitude of IHI is decreased (Ferbert et al, 1992;Daskalakis et al, 2002). We observed no differences in the magnitude of IHI between test MEP2 and test MEP3, and this is also in agreement with previous results (Gilio et al, 2003).…”

Motorcortical Excitability and Synaptic Plasticity Is Enhanced in Professional Musicians

“…The steep slope of the SICIcurve in musicians may allow more effective control of enhanced plasticity and benefit performance. This might be not the case in focal dystonia, because some studies have described reduced SICI at rest (Ridding et al, 1995;Gilio et al, 2003), although this finding is inconsistent (Stinear and Byblow, 2004a,b;Butefisch et al, 2005;Rosenkranz et al, 2005).…”

Use-Dependent Hemispheric Balance

“…Altogether, these findings raised the hypothesis that reduction of excitability in the intact hemisphere may contribute to improvements of motor function in stroke (Hummel and Cohen, 2006). Accordingly, previous studies in healthy volunteers showed that downregulation of excitability in one motor cortex, by repetitive TMS (rTMS) on that area, results in an increased excitability of the opposite motor cortex and an improved motor performance of the ipsilateral hand (Gilio et al, 2003;Kobayashi et al, 2004;Avanzino et al, 2008). Here, to directly investigate cortical modifications induced by an abnormal asymmetric use of the two limbs, we propose an experimental approach based on short-term hand immobilization in healthy volunteers.…”