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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.

Author information

1
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.
2
Nexstim Plc, Elimäenkatu 9 B, FI-00510 Helsinki, Finland.

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.

KEYWORDS:

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

PMID:
27215172
DOI:
10.1016/j.medengphy.2016.04.025
[Indexed for MEDLINE]

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