Coil design for real and sham transcranial magnetic stimulation

Transcranial magnetic stimulation (TMS) can be used to excite the human cor tex noninvasively TMS also activates scalp muscles and sensory receptors; a dditionally, the loud sound from the stimulating coil activates auditory pa thways, These side effects complicate the interpretation of the results of TMS studies. For control experiments, we have designed a coil that can prod uce both real and sham stimulation without moving the coil. The sham TMS is similar to the real TMS, except for the different relative direction of th e currents in the two loops of the figure-of-eight coil. While the real TMS elicited activation of hand muscles, sham TMS had no such effect; however, the auditory-evoked potentials were similar.