The Effects of Repetitive Transcranial Magnetic Stimulation in Healthy Human Subjects

It has been suggested that the therapeutic effects of repetitive transcranial magnetic stimulation (rTMS) are mediated through changes in cortical inhibition (CI). However, in healthy subjects the effects of rTMS on CI have been inconsistent. The aim of this study is to explore different rTMS - stimulus conditions neurophysiological and molecular mechanisms in the human motor cortex. Fifty-six healthy subjects will be randomized into three different treatment groups and receive 1 active or sham rTMS session (6000 rTMS pulses) at 90% of their motor threshold (MT). Cortical inhibition will be indexed pre and post treatment using short-interval intracortical inhibition (SICI), cortical silent period (CSP) and long-interval cortical inhibition (LICI). Based on previous studies we hypothesize that: * Hypothesis 1: rTMS will result in a greater CI (i.e., prolonged CSP, increased LICI but not SICI) compared to sham rTMS. * Hypothesis 2: 20 Hz rTMS will result in a significantly greater CI compared to 1 Hz rTMS. * Hypothesis 3: There will be distinctive transcription profiles associated with increases in CI from rTMS that can be detected with whole-genome microarray analysis of peripheral leukocytes.