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Near-Threshold Recruitment Characteristics of Motor Evoked Potentials in Transcranial Magnetic Stimulation

2022; RELX Group (Netherlands); Linguagem: Inglês

10.2139/ssrn.4174970

1556-5068

Michal Demjan, Laura Säïsänen, Jusa Reijonen, Saara M. Rissanen, Sara Määttä, Petro Julkunen,

Spatial Neglect and Hemispheric Dysfunction

Transcranial magnetic stimulation (TMS) can induce motor evoked potentials (MEPs). In TMS applications, near-threshold stimulation intensities (SIs) are often used for inducing MEPs and characterizing corticospinal excitability. 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 (ppTMS), were included. The probability of MEP (pMEP) 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=0.002), while the relative spread remained similar (p>0.999). At suprathreshold SIs, the probability of MEP was similar between UT and 110% of rMT (pMEP >0.88), and higher for 120% of rMT (pMEP >0.98). The individual near-threshold characteristics determine how probably MEPs are produced at common suprathreshold SIs. At the population level, 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.Funding Information: The study was funded by State research funding (VTR), Academy of Finland (322423), Orion Research Foundation sr and KYS Tutkimussäätiö. J.R. was funded by the Vilho, Yrjö and Kalle Väisälä Foundation of the Finnish Academy of Science and Letters (Helsinki, Finland); and Päivikki and Sakari Sohlberg Foundation (Helsinki, Finland). S.R. and L.S. were funded by the Business Finland (grant no. 2956/31/2018).Conflict of Interests: PJ has an unrelated patent with Nexstim Plc. LS has received travel support from Nexstim Plc. MD, SR, JR and SM declare no conflict of interest.Ethical Approval: The study was approved by the research ethics committee of the Northern Savo Hospital District (statement 72/2016).