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

Pitcher, J.B., Doeltgen, S.H., Goldsworthy, M.R, Schneider, L.A, Vallence, A.M., Smith, A.E, Semmler, J.G, McDonnell, M.N. and Ridding, M.C. (2015) A comparison of two methods for estimating 50% of the maximal motor evoked potential. Clinical Neurophysiology, 126 (12). pp. 2337-2341.

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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 10-74years) 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.

Publication Type: Journal Article
Murdoch Affiliation: School of Psychology and Exercise Science
Publisher: Elsevier
Copyright: © 2015 International Federation of Clinical Neurophysiology.
Notes: Available online 28 February 2015
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