Near-threshold recruitment characteristics of motor evoked potentials in transcranial magnetic stimulation

Michal Demjan; Laura Säisänen; Jusa Reijonen; Saara Rissanen; Sara Määttä; Petro Julkunen

doi:10.1016/j.brainres.2023.148284

Near-threshold recruitment characteristics of motor evoked potentials in transcranial magnetic stimulation

Brain Res. 2023 Apr 15:1805:148284. doi: 10.1016/j.brainres.2023.148284. Epub 2023 Feb 14.

Authors

Michal Demjan¹, Laura Säisänen², Jusa Reijonen³, Saara Rissanen², Sara Määttä⁴, Petro Julkunen⁵

Affiliations

¹ Department of Clinical Neurophysiology, Kuopio University Hospital, POB 100, 70200 KYS Kuopio, Finland; Department of Technical Physics, University of Eastern Finland, POB 1627, 70210 Kuopio, Finland; Bittium Biosignals Oy, Pioneerinkatu 6, 70800 Kuopio, Finland.
² Department of Technical Physics, University of Eastern Finland, POB 1627, 70210 Kuopio, Finland.
³ Department of Clinical Neurophysiology, Kuopio University Hospital, POB 100, 70200 KYS Kuopio, Finland; Department of Technical Physics, University of Eastern Finland, POB 1627, 70210 Kuopio, Finland.
⁴ Department of Clinical Neurophysiology, Kuopio University Hospital, POB 100, 70200 KYS Kuopio, Finland.
⁵ Department of Clinical Neurophysiology, Kuopio University Hospital, POB 100, 70200 KYS Kuopio, Finland; Department of Technical Physics, University of Eastern Finland, POB 1627, 70210 Kuopio, Finland. Electronic address: petro.julkunen@uef.fi.

PMID: 36796474
DOI: 10.1016/j.brainres.2023.148284

Abstract

Transcranial magnetic stimulation (TMS) can induce motor evoked potentials (MEPs). In TMS applications, near-threshold stimulation intensities (SIs) are often used for characterizing corticospinal excitability using MEPs. We aimed to characterize the individual near-threshold recruitment of MEPs and to test the assumptions related to selection of the suprathreshold SI. We utilized MEP data from a right-hand muscle induced at variable SIs. The single-pulse TMS (spTMS) data from previous studies (27 healthy volunteers), as well as data from new measurements (10 healthy volunteers) that included also MEPs modulated by paired-pulse TMS (ppTMS), were included. The probability of MEP (p_MEP) was represented with individually fitted cumulative distribution function (CDF) with two parameters: resting motor threshold (rMT) and spread relative to rMT. MEPs were recorded with 110% and 120% of rMT as well as with Mills-Nithi upper threshold (UT). The individual near-threshold characteristics varied with CDF parameters: the rMT and the relative spread (median: 0.052). The rMT was lower with ppTMS than with spTMS (p < 0.001), while the relative spread remained similar (p = 0.812). At suprathreshold SIs, the probability of MEP was similar between UT and 110% of rMT (p_MEP > 0.88), and higher for 120% of rMT (p_MEP > 0.98). The individual near-threshold characteristics determine how probably MEPs are produced at common suprathreshold SIs. At the population level, the used SIs UT and 110% of rMT produced MEPs at similar probability. The individual variability in the relative spread parameter was large; therefore, the method of determining the proper suprathreshold SI for TMS applications is of crucial importance.

Keywords: MEP; Motor evoked potentials; Motor threshold; Recruitment curve; Stimulation Intensity; Transcranial magnetic stimulation.

Publication types

Research Support, Non-U.S. Gov't

MeSH terms

Electromyography
Evoked Potentials, Motor / physiology
Hand
Humans
Motor Cortex* / physiology
Muscle, Skeletal / physiology
Transcranial Magnetic Stimulation* / methods