Objective: To clarify the neurophysiological after-effect of repetitive transcranial magnetic stimulation (rTMS) over supplementary motor area (SMA) which had been shown to improve motor symptoms in Parkinson’s disease (PD).

Background: It is well known that after-effects of rTMS over primary motor cortex (M1) are stimulation frequency dependent: low-frequency stimulation induces suppression of cortical excitability whereas high-frequency rTMS produces facilitation. In contrast, such stimulation frequency dependency has not been clearly shown in rTMS over SMA. Given that both low- (1Hz) and high-frequency (5Hz) rTMS over SMA improve motor symptoms in PD compared with realistic sham stimulation (i.e. placebo stimulation) (Hamada et al., 2008; Shirota et al., 2013), neurophysiological after-effects of low and high frequency rTMS over SMA could be different from those over M1. We therefore investigated the effects of 1 Hz, 5 Hz and 10 Hz rTMS over SMA on motor cortical excitability.

Method: Subjects were seventeen right-handed healthy volunteers (12 men, mean age 30.9 ± 6.5 years). rTMS consists of total 1000 pulses of 1 Hz, 5 Hz, 10 Hz and realistic sham stimulation over SMA at intensity of 110% active motor threshold for the tibialis anterior (TA) muscle. We recorded motor evoked potentials (MEP) from the right first dorsal interosseous (FDI) muscle and measured MEP amplitudes, short-intracortical inhibition (SICI) and intracortical facilitation (ICF) at the timing as follows: before, immediately (T0), 15 min (T15) and 30 min (T30) after the end of each rTMS condition.

Results: We found significant MEP changes after 1Hz rTMS (suppression) and 10 Hz rTMS (facilitation), whereas no changes after 5Hz rTMS and realistic sham stimulation. SICI and ICF did not show significant changes after any rTMS conditions.

Conclusion: Although our results showed that after-effects of rTMS over SMA were stimulation frequency-dependent, 5 Hz rTMS did not show any significant MEP changes, indicating that stimulation frequency dependency seems to be different between M1 and SMA. Furthermore, even though both low and high frequency rTMS have a similar therapeutic effect for PD, the results showed that neurophysiological after-effects are different between conditions, suggesting that behavioural effects of rTMS may not necessarily be comparable to neurophysiological effects.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/effect-of-rtms-over-supplementary-motor-area-on-motor-cortical-excitability-a-study-using-realistic-sham-stimulation-as-placebo/