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A comparison of two methods for estimating 50% of the maximal motor evoked potential

journal contribution
posted on 2015-12-01, 00:00 authored by Julia Pitcher, S H Doeltgen, M R Goldsworthy, L A Schneider, A M Vallence, A E Smith, J G Semmler, M N McDonnell, M C Ridding
© 2015 International Federation of Clinical Neurophysiology. Objectives: Two commonly-used methods for setting stimulus intensities in transcranial magnetic brain stimulation studies were compared to determine which best approximated a motor evoked potential (MEP) of 50% of the maximal MEP amplitude (SI50); a suprathreshold intensity relative to resting motor threshold (rMT) or adjusting the intensity to evoke an MEP amplitude of 1mV. Methods: Corticomotor stimulus-response curves and rMT for the right first dorsal interosseous (FDI) muscle of 176 subjects (aged 10-74. years) were retrospectively analysed. Results: Regardless of subject age or sex, SI50 occurred at 127.5±11.3% rMT. Except in young children, MEPs of 1mV were significantly smaller than those evoked at SI50. Conclusions: In the inactive FDI muscle, a stimulus intensity of 127-128% rMT consistently gives the best approximation of SI50 in most subjects, except perhaps young children. Significance: Setting TMS stimulus intensities relative to rMT provides a less variable inter-subject comparator, with respect to individual differences in corticomotor input-output characteristics, than adjusting the stimulator output to give an absolute MEP magnitude.

History

Journal

Clinical Neurophysiology

Volume

126

Issue

12

Pagination

2337 - 2341

Publisher

Elsevier

Location

Amsterdam, The Netherlands

ISSN

1388-2457

eISSN

1872-8952

Language

eng

Publication classification

C1 Refereed article in a scholarly journal

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