Figure 6. The response of Human motor cortex to rfTMS.

a) The cloverleaf coil is positioned over the motor cortex. Stimuli with constant strength are applied at 0.2 Hz. Individual muscle evoked potentials recorded from the first dorsal interosseous are shown in grey, and the averaged response in black. Rotating the coil by 50° in the plane of the cloverleaf coil and maintaining the center position does not change the amplitude of the muscle response. Data obtained from subject A.N. b) Extended experiment, testing 5 different orientations, controlled by a robotic device. For each orientation two opposite rotation directions of the rotating field were tested. The experiment was then repeated using a standard figure-eight coil, used to apply both biphasic pulses, as in rfTMS, and mono-phasic pulses. Under standard TMS no muscle response can be detected for orientations more than 45° away from the optimum. In contrast, rfTMS provides reliable stimulation independent of the coil's orientation. Data obtained from subject W.P.