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This Article Full Text Full Text (PDF) All Versions of this Article: 586/18/4489    most recent jphysiol.2008.156596v1 Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Google Scholar Articles by Suppa, A. Articles by Rothwell, J. C. PubMed PubMed Citation Articles by Suppa, A. Articles by Rothwell, J. C. Related Collections Neuroscience

¹ Sobell Department of Motor Neuroscience and Movement Disorders, Institute of Neurology, University College London, London, UK
² Department of Neurological Sciences
³ Neuromed Institute, Sapienza University of Rome, Rome, Italy
⁴ Department of Biomedical Sciences, Section of Human Physiology and Bioengineering
⁵ Institute of Neurology, University of Sassari, Sassari, Italy
⁶ Department of Clinical Neurophysiology, Georg-August-University, Göttingen, Germany

Interhemispheric interactions between the primary motor cortices (M1) have been described with a variety of TMS methods. Here we give a detailed description of the interhemispheric interactions of a period of theta burst simulation (TBS), a rapid method of producing long lasting after-effects on the excitability of the stimulated M1. A total of 18 right handed healthy subjects participated. In most experiments, continuous and intermittent TBS (cTBS and iTBS) were delivered over the right M1 using a coil orientated to induce antero-posterior followed by postero-anterior (AP–PA) currents in the brain. The intensity of stimulation was 80% of active motor threshold (AMT), and a total of 600 pulses were applied. The effects on the amplitude of motor evoked potentials (MEPs), short interval intracortical inhibition (SICI) and intracortical facilitation (ICF) were evaluated in the left and right M1 before and at three different times after TBS. We also tested long-interval intracortical inhibition (LICI) in right M1 and interhemispheric inhibition (IHI) from right to left M1. Finally, to explore the effect of different polarities of cTBS over dominant and non-dominant hemisphere we delivered AP–PA and postero-anterior followed by antero-posterior (PA–AP) cTBS over either right or left M1 and tested MEPs in both hemispheres. In the stimulated hemisphere, cTBS reduced MEPs and SICI whereas iTBS increased MEPs and SICI. In the non-stimulated hemisphere cTBS increased MEPs and reduced SICI, while iTBS reduced MEPs and increased SICI. There were no effects on ICF, LICI or IHI. Although both AP–PA cTBS and PA–AP cTBS reduced MEPs in the stimulated M1, the former increased MEPs from non-stimulated M1 whereas the latter did not. There was no difference in the effect of cTBS on the dominant or non-dominant hemisphere.

(Received 9 May 2008; accepted after revision 23 July 2008; first published online 31 July 2008)
Corresponding author J. C. Rothwell: Sobell Department of Motor Neuroscience and Movement Disorders, Institute of Neurology, University College London, 8–11 Queen Square, London WC1N 3BG, UK.  Email: j.rothwell{at}ion.ucl.ac.uk