title: Facilitatory effect of paired-pulse stimulation by transcranial magnetic stimulation with biphasic wave-form.
abstract: Transcranial magnetic stimulation (TMS) is used to probe corticospinal excitability by stimulating the motor cortex. Our aim was to enhance the effects of biphasic TMS by coupling a suprathreshold test pulse and a following subthreshold priming pulse to induce short-interval intracortical facilitation (SICF), which is conventionally produced with monophasic TMS. Biphasic TMS could potentially induce the SICF effect with better energy-efficiency and with lower stimulus intensities. This would make the biphasic paired-pulses better applicable in patients with reduced cortical excitability. A prototype stimulator was built to produce biphasic paired-pulses. Resting motor thresholds (rMTs) from the right and left hand abductor pollicis brevis muscles, and the right tibialis anterior muscle of eight healthy volunteers were determined using single-pulse paradigm with neuronavigated TMS. The rMTs and MEPs were measured using single-pulses and three paired-pulse setups (interstimulus interval, ISI of 3, 7 or 15ms). The rMTs were lower and MEPs were higher with biphasic paired-pulses compared to single-pulses. The SICF effect was greatest at 3ms ISI. This suggests that the application of biphasic paired-pulses to enhance stimulation effects is possible.
authors.affiliation: Department of Clinical Neurophysiology, Kuopio University Hospital, Kuopio, Finland; Department of Applied Physics, University of Eastern Finland, Kuopio, Finland. Electronic address: petro.julkunen@kuh.fi.
authors.forename: Petro
authors.initials: P
authors.lastname: Julkunen
authors.affiliation: Nexstim Plc, Elimäenkatu 9 B, FI-00510 Helsinki, Finland.
authors.forename: Gustaf
authors.initials: G
authors.lastname: Järnefelt
authors.affiliation: Nexstim Plc, Elimäenkatu 9 B, FI-00510 Helsinki, Finland.
authors.forename: Petri
authors.initials: P
authors.lastname: Savolainen
authors.affiliation: Nexstim Plc, Elimäenkatu 9 B, FI-00510 Helsinki, Finland.
authors.forename: Jarmo
authors.initials: J
authors.lastname: Laine
authors.affiliation: Nexstim Plc, Elimäenkatu 9 B, FI-00510 Helsinki, Finland.
authors.forename: Jari
authors.initials: J
authors.lastname: Karhu
mesh_terms: D000328:Adult; D005260:Female; D006801:Humans; D008297:Male; D018482:Muscle, Skeletal / Q000502:physiology; D050781:Transcranial Magnetic Stimulation / Q000379:methods*
keywords: Biphasic wave-form; Motor evoked potential; Motor threshold; Paired-pulse; Short-interval intracortical facilitation; Transcranial magnetic stimulation