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Med Eng Phys. 2016 Aug;38(8):813-7. doi: 10.1016/j.medengphy.2016.04.025. Epub 2016 May 20.

Facilitatory effect of paired-pulse stimulation by transcranial magnetic stimulation with biphasic wave-form.

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Department of Clinical Neurophysiology, Kuopio University Hospital, Kuopio, Finland; Department of Applied Physics, University of Eastern Finland, Kuopio, Finland. Electronic address:
Nexstim Plc, Elimäenkatu 9 B, FI-00510 Helsinki, Finland.


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.


Biphasic wave-form; Motor evoked potential; Motor threshold; Paired-pulse; Short-interval intracortical facilitation; Transcranial magnetic stimulation

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