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J Physiol Volume 574, Number 2, 443-455, July 15, 2006 DOI: 10.1113/jphysiol.2006.108464
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NEUROSCIENCE

Effects of repetitive TMS on visually evoked potentials and EEG in the anaesthetized cat: dependence on stimulus frequency and train duration

Selcen Aydin-Abidin1,2, Vera Moliadze1, Ulf T. Eysel1,2 and Klaus Funke1,2

1 Department of Neurophysiology, Faculty of Medicine
2 International Graduate School of Neuroscience (IGSN), Ruhr-University Bochum, Bochum, Germany

Repetitive transcranial magnetic stimulation (rTMS) has been shown to alter cortical excitability that lasts beyond the duration of rTMS application itself. High-frequency rTMS leads primarily to facilitation, whereas low-frequency rTMS leads to inhibition of the treated cortex. However, the contribution of rTMS train duration is less clear. In this study, we investigated the effects of nine different rTMS protocols, including low and high frequencies, as well as short and long applications (1, 3 and 10 Hz applied for 1, 5 and 20 min), on visual cortex excitability in anaesthetized and paralysed cats by means of visual evoked potential (VEP) and electroencephalography (EEG) recordings. Our results show that 10 Hz rTMS applied for 1 and 5 min significantly enhanced early VEP amplitudes, while 1 and 3 Hz rTMS applied for 5 and 20 min significantly reduced them. No significant changes were found after 1 and 3 Hz rTMS applied for only 1 min, and 10 Hz rTMS applied for 20 min. EEG activity was only transiently (<20 s) affected, with increased delta activity after 1 and 3 Hz rTMS applied for 1 or 5 min. These findings indicate that the effects of rTMS on cortical excitability depend on the combination of stimulus frequency and duration (or total number of stimuli): short high-frequency trains seem to be more effective than longer trains, and low-frequency rTMS requires longer applications. Changes in the spectral composition of the EEG were not correlated to changes in VEP size.

(Received 27 February 2006; accepted after revision 5 May 2006; first published online 11 May 2006)
Corresponding author K. Funke: Department of Neurophysiology, Medical Faculty, Ruhr-University Bochum, Universitaetstrasse 150, 44780 Bochum, Germany. Email: funke{at}neurop.ruhr-uni-bochum.de






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