The number of full-sine cycles per pulse influences the efficacy of multicycle transcranial magnetic stimulation Astrid Pechmann, a Igor Delvendahl, a Til O. Bergmann, b Christoph Ritter, b Gesa Hartwigsen, b Bernhard Gleich, c Norbert Gattinger, c,d Volker Mall, a Hartwig R. Siebner b,e a Division of Neuropaediatrics and Muscular Disorders, Department of Paediatrics and Adolescent Medicine, University Hospital Freiburg, Freiburg, Germany b Department of Neurology, Christian-Albrechts-University, Kiel, Germany c Zentralinstitut f€ ur Medizintechnik (IMETUM), Technische Universit€ at M€ unchen, M€ unchen, Germany d Heinz Nixdorf-Lehrstuhl f€ ur Medizinische Elektronik, Technische Universit€ at M€ unchen, M€ unchen, Germany e Danish Research Centre for Magnetic Resonance, Copenhagen University Hospital Hvidovre, Hvidovre, Denmark Background Previous studies have shown that the efficacy of transcranial magnetic stimulation (TMS) to excite corticospinal neurons depends on pulse waveform. Objective/Hypotheses In this study, we examined whether the effectiveness of polyphasic TMS can be increased by using a pulse profile that consists of multiple sine cycles. Methods In eight subjects, single-pulse TMS was applied to the left primary motor hand area through a round coil attached to a stimulator device that generated polyphasic pulses consisting of one to six full-sine cycles with a cycle length of 86 ms. In different blocks, we varied the number of sine cycles per pulse and recorded the motor-evoked potential (MEP) from the right first dorsal interosseus muscle. For each stimulus type, we determined resting motor threshold (RMT), stimulus-response curve (SRC), and mean MEP amplitude evoked at maximal stimulator output to assess the efficacy of stimulation. Results Multicycle pulses were more effective than a single full-sine cycle in exciting corticospinal neurons. TMS with multicycle pulses resulted in lower RMT, larger MEP amplitudes at maximal stimulator output and a steeper slope of the SRC relative to a TMS pulse consisting of a single-sine cycle. The increase in efficacy was already evident when two full-sine cycles were used and did not increase further by adding more cycles to the TMS pulse. B. Gleich, and N. Gattinger are supported by the Bayerische Forschungsstiftung BFS under grant number AZ742/02. Correspondence: Professor Hartwig R. Siebner, M.D., Danish Research Centre for Magnetic Resonance (DRCMR), Copenhagen University Hospital Hvidovre, Ketteg  ards All e 30, 2650 Hvidovre, Denmark. E-mail address: hartwig.siebner@drcmr.dk Submitted October 19, 2010; revised February 23, 2011. Accepted for publication February 25, 2011. 1935-861X/$ - see front matter Ó 2012 Elsevier Inc. All rights reserved. doi:10.1016/j.brs.2011.02.006 Brain Stimulation (2012) 5, 148–54 www.brainstimjrnl.com