Restorative Neurology and Neuroscience 34 (2016) 859–868 DOI 10.3233/RNN-160664 IOS Press 859 After-effects of anodal transcranial direct current stimulation on the excitability of the motor cortex in rats Ho Koo a , Min Sun Kim a , Sang Who Han a , Walter Paulus b , Michael A. Nitche c , Yun-Hee Kim d , Hyoung-Ihl Kim e , Sung-Hwa Ko f and Yong-Il Shin f ,∗ a Department of Physiology, Wonkwang University College of Medicine, Iksan, South Korea b University Medical Center, Department Clinical Neurophysiology, Georg-August-University, Goettingen, Germany c University Medical Center, Department Clinical Neurophysiology, Georg-August-University, Goettingen, Germany; Leibniz Research Center for Working Environment and Human Factors, Dortmund, Germany; Department of Neurology, BG University Hospital Bergmannsheil, Ruhr-University Bochum, Germany d Department of Physical and Rehabilitation Medicine, Center for Prevention and Rehabilitation, Heart Vascular Stroke Institute, Samsung Medical Center, Sungkyunkwan University School of Medicine, Seoul, South Korea e Department of Medical System Engineering & Department of Mechatronics, Gwangju Institute of Science and Technology, Gwangju, South Korea f Department of Rehabilitation Medicine, Pusan National University School of Medicine, Research Institute for Convergence of Biomedical Science and Technology, Pusan National University Yangsan Hospital, Yangsan, South Korea Abstract. Purpose: Transcranial direct current stimulation (tDCS) is increasingly seen as a useful tool for noninvasive cortical neu- romodulation. A number of studies in humans have shown that when tDCS is applied to the motor cortex it can modulate cortical excitability. It is especially interesting to note that when applied with sufficient duration and intensity, tDCS can enable long-lasting neuroplastic effects. However, the mechanism by which tDCS exerts its effects on the cortex is not fully understood. We investigated the effects of anodal tDCS under urethane anesthesia on field potentials in in vivo rats. Methods: These were measured on the skull over the right motor cortex of rats immediately after stimulating the left corpus callosum. Results: Evoked field potentials in the motor cortex were gradually increased for more than one hour after anodal tDCS. To induce these long-lasting effects, a sufficient duration of stimulation (20 minutes or more) was found to may be required rather than high stimulation intensity. Conclusion: We propose that anodal tDCS with a sufficient duration of stimulation may modulate transcallosal plasticity. Keywords: Transcranial direct stimulation, cerebral cortex, cortical excitability, neurophysiology, rat ∗ Corresponding author: Yong-Il Shin, MD, PhD, Department of Rehabilitation Medicine, Pusan National University School of Medicine, Research Institute for Convergence of Biomedical Science and Technology, Pusan National University Yangsan Hos- pital, Yangsan, Zip. 626-770, South Korea. Tel.: +82 10 6535 0310; E-mail: rmshin01@gmail.com. 1. Introduction Transcranial direct current stimulation (tDCS) is a promising tool for cortical neuromodulation. In many human studies, it has been successfully used for the modulation of cortical excitability (Antal, Kincses, 0922-6028/16/$35.00 © 2016 – IOS Press and the authors. All rights reserved