Single-pulse and paired-pulse TMS reveal spatially distinct corticomotor maps in human motor cortex
Poster No:
122
Submission Type:
Abstract Submission
Authors:
Mads Madsen1, Lasse Christiansen1, Hartwig Siebner1
Institutions:
1Danish Research Centre for Magnetic Resonance (DRCMR), Copenhagen, Denmark
First Author:
Co-Author(s):
Introduction:
Transcranial magnetic stimulation (TMS) of the primary motor hand area (M1-HAND) can probe corticomotor physiology by recording motor evoked potentials (MEP) in contralateral hand muscles (Barker, Jalinous et al. 1985). Paired-pulse TMS at peri-threshold intensity induce short-latency intracortical facilitation (SICF) at distinct interstimulus intervals (ISIs). The first two peaks of SICF occur at inter-pulse intervals (IPIs) of around 1.0-1.5 ms (SICF1) and 2.4-2.9 ms (SICF2)(Ziemann, Tergau et al. 1998) mimicking the timing of indirect (I)-waves recorded from the spinal cord (Di Lazzaro, Oliviero et al. 1998).
Objective: To test the hypothesis that SICF is generated by intracortical circuits that are spatially distinct from the circuits evoking single-pulse MEPs.
Objective: To test the hypothesis that SICF is generated by intracortical circuits that are spatially distinct from the circuits evoking single-pulse MEPs.
Methods:
In 14 healthy subjects we used neuronavigated biphasic TMS over the left sensorimotor hand area to construct sulcus-shaped corticomotor maps following a 7x3 grid (figure 1)(Raffin, Pellegrino et al. 2015). We constructed a total of three motor maps using single-pulse TMS and paired-pulse TMS targeting individual SICF1 and SICF2 peak latencies. Maps were constructed for both the right first-dorsal interosseous (FDI) and abductor digiti minimi (ADM) muscles. We calculated map area, volume, and center of gravity (CoG) for each corticomotor map and for each muscle.
·Figure 1. Overview of methodological approach
Results:
Paired-pulse SICF TMS resulted in larger corticomotor maps than single-pulse TMS (P<0.001). For both hand muscles, SICF maps consistently showed a posterior shift of CoGs towards the central sulcus relative to the CoG derived from single-pulse maps (SICF2: 0.62 +/- 0.21, P=0.01, SICF1: 1.28, +/- 0.21, P<0.001). The CoG shift was more pronounced for the SICF1 compared to SICF2 map (0.66 +/- 0.21, P=0.005)(figure 2). ADM and FDI maps consistently displayed a medial-to-lateral segregation in all maps (P<0.001).
·Figure 2. Individual (small) and mean (large), within subject mean adjusted CoGs in the PC1 and PC2 axes. For visualization purposes only.
Conclusions:
SICF-generating circuits have a more posterior corticomotor representation in the precentral crown than single pulse MEP generating circuits. This finding indicates that spatially distinct cortical circuits are engaged by paired pulse TMS probing SICF compared to single-pulse TMS, at least when using biphasic pulses. The findings also support the notion that spatially distinct circuits are involved in the generation of the first and second SICF peaks.
Brain Stimulation:
Non-invasive Magnetic/TMS
TMS 1
Motor Behavior:
Motor Behavior Other
Neuroanatomy, Physiology, Metabolism and Neurotransmission:
Cortical Anatomy and Brain Mapping 2
Keywords:
Cortex
Motor
Transcranial Magnetic Stimulation (TMS)
1|2Indicates the priority used for review
Provide references using author date format
Di Lazzaro, V., A. Oliviero, P. Profice, E. Saturno, F. Pilato, A. Insola, P. Mazzone, P. Tonali and J. C. Rothwell (1998). "Comparison of descending volleys evoked by transcranial magnetic and electric stimulation in conscious humans." Electroencephalogr Clin Neurophysiol 109(5): 397-401.
Raffin, E., G. Pellegrino, V. Di Lazzaro, A. Thielscher and H. R. Siebner (2015). "Bringing transcranial mapping into shape: Sulcus-aligned mapping captures motor somatotopy in human primary motor hand area." Neuroimage 120: 164-175.
Ziemann, U., F. Tergau, E. M. Wassermann, S. Wischer, J. Hildebrandt and W. Paulus (1998). "Demonstration of facilitatory I wave interaction in the human motor cortex by paired transcranial magnetic stimulation." J Physiol 511 ( Pt 1): 181-190.