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Trial-to-trial size variability of motor-evoked potentials. A study using the triple stimulation technique

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Abstract

Motor-evoked potentials (MEPs) vary in size from one stimulus to the next. The objective of this study was to determine the cause and source of trial-to-trial MEP size variability. In two experiments involving 10 and 14 subjects, the variability of MEPs to cortical stimulation (cortical-MEPs) in abductor digiti minimi (ADM) and abductor hallucis (AH) was compared to those responses obtained using the triple stimulation technique (cortical-TST). The TST eliminates the effects of motor neuron (MN) response desynchronization and of repetitive MN discharges. Submaximal stimuli were used in both techniques. In six subjects, cortical-MEP variability was compared to that of brainstem-MEP and brainstem-TST. Variability was greater for MEPs than that for TST responses, by approximately one-third. The variability was the same for cortical- and brainstem-MEPs and was similar in ADM and AH. Variability concerned at least 10–15% of the MN pool innervating the target muscle. With the stimulation parameters used, repetitive MN discharges did not influence variability. For submaximal stimuli, approximately two-third of the observed MEP size variability is caused by the variable number of recruited alpha-MNs and approximately one-third by changing synchronization of MN discharges. The source of variability is most likely localized at the spinal segmental level.

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Acknowledgment

This study was supported by a research grant of the Swiss National Science foundation to KMR and MRM (Grant 3200B0-100701).

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Authors and Affiliations

  1. Department of Neurology, Inselspital, Bern University Hospital and University of Bern, 3010, Bern, Switzerland

    Kai M. Rösler & Denise M. Roth

  2. Department of Neurology, Hôpital Cantonal de Genève, Geneva University, Geneva, Switzerland

    Michel R. Magistris

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  1. Kai M. Rösler
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  2. Denise M. Roth
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  3. Michel R. Magistris
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Correspondence to Kai M. Rösler.

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Rösler, K.M., Roth, D.M. & Magistris, M.R. Trial-to-trial size variability of motor-evoked potentials. A study using the triple stimulation technique. Exp Brain Res 187, 51–59 (2008). https://doi.org/10.1007/s00221-008-1278-z

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  • DOI: https://doi.org/10.1007/s00221-008-1278-z

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