Stimulus waveform influences the efficacy of repetitive transcranial magnetic stimulation.
BACKGROUND
Optimising stimulus parameters is important in maximising the efficacy of repetitive transcranial magnetic stimulation (rTMS) in treatment applications. RTMS over motor cortex has been reported as more effective in producing corticospinal inhibition when a monophasic rather than a biphasic stimulus waveform is used. However, non-optimal coil orientation and high intensities of monophasic rTMS may have influenced previous results.


METHODS
In eight healthy subjects, we measured motor evoked potentials (MEPs) in a hand muscle after monophasic and biphasic rTMS (1 Hz for 15 min) over the motor cortex with the coil always in the optimal orientation. MEPs were evoked by both monophasic and biphasic stimuli.


RESULTS
MEPs were initially significantly reduced after monophasic but not biphasic rTMS. However, a late reduction was seen after biphasic rTMS.


CONCLUSIONS
These motor cortical findings may not be directly applicable to prefrontal rTMS.


CONCLUSIONS
This study confirms that low frequency rTMS with monophasic pulses produces more corticospinal inhibition than with biphasic pulses, even when the direction of current and intensity are as well-matched as possible.
Taylor
Janet L
JL
Prince of Wales Medical Research Institute, Randwick, NSW, Australia.
Loo
Colleen K
CK
D000328:Adult; D004576:Electromyography; D019054:Evoked Potentials, Motor / Q000502:physiology*; D005260:Female; D006225:Hand / Q000294:innervation; D006801:Humans; D008297:Male; D008475:Median Nerve / Q000502:physiology; D009044:Motor Cortex / Q000502:physiology*; D018482:Muscle, Skeletal / Q000294:innervation; D009433:Neural Inhibition / Q000502:physiology; D017397:Prefrontal Cortex / Q000502:physiology; D011712:Pyramidal Tracts / Q000502:physiology; D012016:Reference Values; D012684:Sensory Thresholds / Q000502:physiology; D050781:Transcranial Magnetic Stimulation / Q000379:methods*; D016896:Treatment Outcome