Orientation-specific, non NMDA-receptor dependent facilitation in the human motor cortex elicited by fast biphasic repetitive transcranial magnetic stimulation

Background and methods: To elucidate mechanisms of corticospinal facilitation outlasting 5Hz transcranial magnetic stimulation applied over the human primary motor cortex, we compared monophasic and biphasic pulses of anterior or posterior initial current direction in 8 healthy subjects. We tested six blocks of 200 pulses of each type at 90% active motor threshold and controlled for corticospinal excitability changes using motor evoked potential (MEP) amplitudes and latencies elicited by suprathreshold pulses before, in between and after rTMS. Results: Only with biphasic pulses of initially anterior current dire…