Acute modulation of cortical oscillatory activities during short trains of high‐frequency repetitive transcranial magnetic stimulation of the human motor cortex: A combined EEG and TMS study

Abstract In this study, a combined repetitive transcranial magnetic stimulation/electroencephalography (rTMS/EEG) method was used to explore the acute changes of cortical oscillatory activity induced by intermittent short trains of high‐frequency (5‐Hz) rTMS delivered over the left primary motor cortex (M1). We evaluated the electrophysiological reaction to magnetic stimulation during and 2–4 s after 20 trains of 20‐pulses rTMS, using event‐related power (ERPow) that reflects the regional oscillatory activity of neural assemblies, and event‐related coherence (ERCoh) that reflects the interregional functional connectivity of oscillatory neural activity. These event‐related transformations were for the upper α (10–12 Hz) and β (18–22 Hz) frequency ranges, respectively. For the α band, threshold rTMS and subthreshold rTMS induced an ERPow increase during the trains of stimulation mainly in frontal and central regions ipsilateral to stimulation. For the β band, a similar synchronization of cortical oscillations for both rTMS intensities was seen. Moreover, subthreshold rTMS affected α‐band activity more than threshold rTMS, inducing a specific ERCoh decrease over the posterior regions during the trains of stimulation. For β band, the decrease in functional coupling was observed mainly during threshold rTMS. These findings provide a better understanding of the cortical effects of high‐frequency rTMS, whereby the induction of oscillations reflects the capacity of electromagnetic pulses to alter regional and interregional synaptic transmissions of neural populations. Hum Brain Mapp, 2008. © 2007 Wiley‐Liss, Inc.