Impact of pulse waveform and current direction for single and paired pulse TMS and for repetitive TMS

Abstract

Waveform and current direction determine the effectiveness of transcranial magnetic stimulation in humans. For single pulse TMS these factors have been shown to influence the motor threshold and the silent period duration detected by motor cortex stimulation and the phosphene threshold tested by occipital stimulation, for paired pulses they affect the balance of intracortical inhibition and facilitation within the motor cortex, and for repetitive stimulation the extent and specificity of the induced motor cortex inhibition and facilitation. Possibly, the extent and selectivity of activation of inhibiting and facilitating interneutons depend on TMS waveform and current direction.