Randomising stimulus intensity improves the variability and reliability of the assessment of corticospinal excitability

Jai J Suckley; Timothy J Waters; Michael Tran; Paul J Stapley; Jonathan Shemmell; Joel A Walsh; Darryl J McAndrew

doi:10.1016/j.jneumeth.2020.108813

Randomising stimulus intensity improves the variability and reliability of the assessment of corticospinal excitability

J Neurosci Methods. 2020 Aug 1:342:108813. doi: 10.1016/j.jneumeth.2020.108813. Epub 2020 Jun 17.

Authors

Jai J Suckley¹, Timothy J Waters¹, Michael Tran¹, Paul J Stapley², Jonathan Shemmell³, Joel A Walsh², Darryl J McAndrew⁴

Affiliations

¹ Neural Control of Movement Laboratory, School of Medicine, Faculty of Science, Medicine & Health, University of Wollongong, Northfields Avenue, Wollongong, NSW, 2522, Australia.
² Neural Control of Movement Laboratory, School of Medicine, Faculty of Science, Medicine & Health, University of Wollongong, Northfields Avenue, Wollongong, NSW, 2522, Australia; Illawarra Health & Medical Research Institute (IHMRI), University of Wollongong, Northfields Avenue, Wollongong, NSW, 2522, Australia.
³ Neural Control of Movement Laboratory, School of Medicine, Faculty of Science, Medicine & Health, University of Wollongong, Northfields Avenue, Wollongong, NSW, 2522, Australia; Illawarra Health & Medical Research Institute (IHMRI), University of Wollongong, Northfields Avenue, Wollongong, NSW, 2522, Australia; Neuromotor Research Laboratory, School of Medicine, University of Wollongong, Northfields Avenue, Wollongong, NSW, 2522, Australia.
⁴ Neural Control of Movement Laboratory, School of Medicine, Faculty of Science, Medicine & Health, University of Wollongong, Northfields Avenue, Wollongong, NSW, 2522, Australia; Illawarra Health & Medical Research Institute (IHMRI), University of Wollongong, Northfields Avenue, Wollongong, NSW, 2522, Australia; Discipline of Graduate Medicine, School of Medicine, University of Wollongong, Northfields Avenue, Wollongong, NSW, 2522, Australia. Electronic address: mcandrew@uow.edu.au.

PMID: 32562710
DOI: 10.1016/j.jneumeth.2020.108813

Abstract

Background: Advances in the control of transcranial magnetic stimulation (TMS) have enabled greater randomisation of stimulus intensity. It is unclear if such randomisation improves assessments of corticospinal excitability.

New method: We recorded the amplitude of TMS-induced motor evoked potentials (MEPs) from the first dorsal interosseous muscle of eleven participants, during three TMS protocols: blocks of increasing intensity (IB), randomised blocks (RB) and inter-stimulus randomisation (IR). Stimulus intensities from 90 to 140% of active motor threshold described corticospinal input-output (I/O) properties. The experiment was repeated in five participants.

Results: Although MEP amplitudes did not differ between IB, RB and IR stimulation protocols, variability was lowest in the IR protocol, compared to IB and RB protocols. Reliability was highest in the IR protocol, compared to IB and IR protocols.

Comparison with existing methods: Randomising TMS intensity between each trial produces less variable and more reliable estimates of corticospinal excitability than previously used blocked protocols and produces the same I/O measures.

Conclusions: Inter-trial randomization of TMS intensities appears to be the most reliable method for constructing I/O curves at multiple time points and decreases the variability of responses.

Keywords: Active motor threshold; Corticospinal excitability; Input/output curves; Motor evoked potentials; Transcranial magnetic stimulation; fIrst dorsal interosseous muscle.

MeSH terms

Electromyography
Evoked Potentials, Motor
Humans
Motor Cortex*
Movement
Muscle, Skeletal
Reproducibility of Results
Transcranial Magnetic Stimulation