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Pre-stimulus theta power is correlated with variation of motor evoked potential latency: a single-pulse TMS study

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Abstract

There has been a growing interest in the role of pre-stimulus oscillations on cortical excitability in visual and motor systems. Prior studies focused on the relationship between pre-stimulus neuronal activity and TMS-evoked motor evoked potentials (MEPs) have reported heterogeneous results. We aimed to assess the role of pre-stimulus neural activity on the latency of MEPs, which might enhance our understanding of the variability of MEP signals, and potentially provide information on the role played by cortical activity fluctuations in the excitability of corticospinal pathways. Near-threshold single-pulse TMS (spTMS) was applied at random intervals over the primary motor cortex of 14 healthy participants while they sat passively, to trigger hand muscle contractions. Multichannel EEG was recorded during spTMS blocks. Spearman correlations between both the variation in MEP onset latencies and peak-to-peak MEP amplitudes, and the pre-stimulus power of EEG oscillations were calculated across participants. We found that the variation in MEP latency was positively correlated with pre-stimulus power in the theta range (4–7 Hz) in a broad time window (− 3.1 to − 1.9 s) preceding the spTMS generating the MEP. No correlation between pre-stimulus power in any frequency band and MEP amplitude was found. Our results show that pre-stimulus theta oscillations are correlated with the variation in MEP latency, an outcome measure determined by fiber conduction velocity and synaptic delays along the corticospinal tract. This finding could prove useful for clinicians using MEP latency-based information in pre- or intra-operative diagnostics of corticospinal impairment.

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Acknowledgements

MV was supported by the Fondation pour la Recherche Médicale (FRM). AS was supported by an ERC Starting Grant (640626). AV-C group’s research is supported by IHU-A-ICM-Translationnel, and Agence National de la Recherche (ANR), projet Générique OSCILOSCOPUS and eraNET-JTC-HBP CAUSALTOMICS. Authors would like to thank Julià L Amengual from Brain dynamics, Cognition and Rehabilitation Group, Frontlab Team, Institut du Cerveau et de la Moelle Epinière (ICM), Paris, France, for his valuable comments and suggestions on the manuscript.

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Correspondence to Zafer İşcan or Antoni Valero-Cabré.

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İşcan, Z., Schurger, A., Vernet, M. et al. Pre-stimulus theta power is correlated with variation of motor evoked potential latency: a single-pulse TMS study. Exp Brain Res 236, 3003–3014 (2018). https://doi.org/10.1007/s00221-018-5359-3

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  • DOI: https://doi.org/10.1007/s00221-018-5359-3

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