Influence of Waveform and Current Direction on Short-Interval Intracortical Facilitation: A Paired-Pulse TMS Study

TY - JOUR

T1 - Influence of Waveform and Current Direction on Short-Interval Intracortical Facilitation

T2 - A Paired-Pulse TMS Study

AU - Delvendahl, Igor

AU - Lindemann, Hannes

AU - Jung, Nikolai H

AU - Pechmann, Astrid

AU - Siebner, Hartwig R

AU - Mall, Volker

N1 - Copyright © 2014 Elsevier Inc. All rights reserved.

PY - 2014/1

Y1 - 2014/1

N2 - Transcranial magnetic stimulation (TMS) of the human primary motor hand area (M1-HAND) can produce multiple descending volleys in fast-conducting corticospinal neurons, especially so-called indirect waves (I-waves) resulting from trans-synaptic excitation. Facilitatory interaction between these I-waves can be studied non-invasively using a paired-pulse paradigm referred to as short-interval intracortical facilitation (SICF). Objective/hypothesis We examined whether SICF depends on waveform and current direction of the TMS pulses. Methods In young healthy volunteers, we applied single- and paired-pulse TMS to M1-HAND. We probed SICF by pairs of monophasic or half-sine pulses at suprathreshold stimulation intensity and inter-stimulus intervals (ISIs) between 1.0 and 5.0 ms. For monophasic paired-pulse stimulation, both pulses had either a posterior-anterior (PA) or anterior-posterior (AP) current direction (AP-AP or PA-PA), whereas current direction was reversed between first and second pulse for half-sine paired-pulse stimulation (PA-AP and AP-PA). Results Monophasic AP-AP stimulation resulted in stronger early SICF at 1.4 ms relative to late SICF at 2.8 and 4.4 ms, whereas monophasic PA-PA stimulation produced SICF of comparable size at all three peaks. With half-sine stimulation the third SICF peak was reduced for PA-AP current orientation compared with AP-PA. Conclusion SICF elicited using monophasic as well as half-sine pulses is affected by current direction at clearly suprathreshold intensities. The impact of current orientation is stronger for monophasic compared with half-sine pulses. The direction-specific effect of paired-pulse TMS on the strength of early versus late SICF shows that different cortical circuits mediate early and late SICF.

AB - Transcranial magnetic stimulation (TMS) of the human primary motor hand area (M1-HAND) can produce multiple descending volleys in fast-conducting corticospinal neurons, especially so-called indirect waves (I-waves) resulting from trans-synaptic excitation. Facilitatory interaction between these I-waves can be studied non-invasively using a paired-pulse paradigm referred to as short-interval intracortical facilitation (SICF). Objective/hypothesis We examined whether SICF depends on waveform and current direction of the TMS pulses. Methods In young healthy volunteers, we applied single- and paired-pulse TMS to M1-HAND. We probed SICF by pairs of monophasic or half-sine pulses at suprathreshold stimulation intensity and inter-stimulus intervals (ISIs) between 1.0 and 5.0 ms. For monophasic paired-pulse stimulation, both pulses had either a posterior-anterior (PA) or anterior-posterior (AP) current direction (AP-AP or PA-PA), whereas current direction was reversed between first and second pulse for half-sine paired-pulse stimulation (PA-AP and AP-PA). Results Monophasic AP-AP stimulation resulted in stronger early SICF at 1.4 ms relative to late SICF at 2.8 and 4.4 ms, whereas monophasic PA-PA stimulation produced SICF of comparable size at all three peaks. With half-sine stimulation the third SICF peak was reduced for PA-AP current orientation compared with AP-PA. Conclusion SICF elicited using monophasic as well as half-sine pulses is affected by current direction at clearly suprathreshold intensities. The impact of current orientation is stronger for monophasic compared with half-sine pulses. The direction-specific effect of paired-pulse TMS on the strength of early versus late SICF shows that different cortical circuits mediate early and late SICF.

KW - Adult

KW - Evoked Potentials, Motor

KW - Female

KW - Humans

KW - Male

KW - Motor Cortex

KW - Transcranial Magnetic Stimulation

KW - Young Adult

U2 - 10.1016/j.brs.2013.08.002

DO - 10.1016/j.brs.2013.08.002

M3 - Journal article

C2 - 24075915

SN - 1935-861X

VL - 7

SP - 49

EP - 58

JO - Brain Stimulation

JF - Brain Stimulation

IS - 1

ER -