1 Department of Neurology, Massachusetts General Hospital, Harvard Medical School, Boston, MA, USA Physical Medicine and Rehabilitation, Feinberg School of Medicine, Northwestern University, Chicago, IL, USA Berenson-Allen Center for Noninvasive Brain Stimulation, Department of Neurology, Beth Israel Deaconess Medical Center, Harvard Medical School, Boston, MA, USA US National Institutes of Health, National Institute on Mental Health, Experimental Therapeutics and Pathophysiology Branch, Bethesda, MD, USA Pain Research Institute, Neuroscience Research Centre, The Walton Centre NHS Foundation Trust, Liverpool, United Kingdom Department of Neurosurgery, Johns Hopkins Medical Institutions, Baltimore, MD, USA EA 4391, Service de Physiologie-Explorations Fonctionnelles, Hôpital Henri Mondor, Faculté de Médecine de Créteil, Université Paris Est Créteil, Créteil, France Human Motor Control Section, Medical Neurology Branch, National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, MD, USA Division of Neurological and Physical Medicine Devices, Office of Device Evaluation, Center for Devices and Radiological Health, US Food and Drug Administration, Bethesda, MD, USA Departments of Anesthesiology, Medicine, and Public Health and Community Medicine, Tufts University School of Medicine, Boston, MA, USA Department of Pathology (Neuropathology), Massachusetts General Hospital, Boston, MA, USA.