1 Berenson-Allen Center for Noninvasive Brain Stimulation, Harvard Medical School and Beth Israel Deaconess Medical Center, 330 Brookline Avenue, Boston, MA, USA; Department of Anatomy and Neurobiology, Boston University School of Medicine, 700 Albany Street, Boston, MA, USA. Electronic address: jsilvant@bidmc.harvard.edu.
2 Institute of Cognitive Neuroscience and Department of Psychology, University College London, Alexandra House, 17 Queen Square, London WC1N 3AR, UK.