Transcranial Magnetic Stimulation Study

Transcranial magnetic stimulation (TMS) is an attractive research and possibly therapeutic tool for non-invasive central nervous system stimulation. However, relatively little is known about the direction, magnitude and distribution of induced electric field and current flows in tissue, and optimal setup characteristics as well as appropriate sham stimulation conditions remain largely undetermined, hampering reproducibility. Asymmetric charge-balanced stimulation waveforms are defined and used for central nervous system stimulation with selective stimulation of either neuronal cell bodies or axon fibers of passage in favour of the other. A pre-pulse is followed by an opposite polarity stimulation pulse, with the pre-pulse being relatively low-amplitude and long-duration as compared to the stimulation pulse. The polarity of the pre-pulse and stimulation pulse control the selectivity of stimulation with respect to neuronal cell bodies versus axon fibers of passage. The waveform used in the stimulation method optionally includes a zero-amplitude phase having a duration of 0 to 500 microseconds.