Distance-adjusted motor threshold for transcranial magnetic stimulation

Stokes, Mark G., Chambers, Christopher D., Gould, Ian C., English, Therese, McNaught, Elizabeth, McDonald, Odette and Mattingley, Jason B. (2007) Distance-adjusted motor threshold for transcranial magnetic stimulation. Clinical Neurophysiology, 118 7: 1617-1625. doi:10.1016/j.clinph.2007.04.004


Author Stokes, Mark G.
Chambers, Christopher D.
Gould, Ian C.
English, Therese
McNaught, Elizabeth
McDonald, Odette
Mattingley, Jason B.
Title Distance-adjusted motor threshold for transcranial magnetic stimulation
Journal name Clinical Neurophysiology   Check publisher's open access policy
ISSN 1388-2457
Publication date 2007-07-01
Sub-type Article (original research)
DOI 10.1016/j.clinph.2007.04.004
Volume 118
Issue 7
Start page 1617
End page 1625
Total pages 9
Place of publication Amsterdam
Publisher Elsevier
Language eng
Subject 170101 Biological Psychology (Neuropsychology, Psychopharmacology, Physiological Psychology)
Abstract Objective To examine the relationship between coil–cortex distance and effective cortical stimulation using transcranial magnetic stimulation (TMS) in the left and right motor cortex. We also compare the effect of coil–cortex distance using 50 and 70 mm figure-eight stimulating coils. Methods Coil–cortex distance was manipulated within each participant using 5 and 10 mm acrylic separators placed between the coil and scalp surface. The effect of cortical stimulation was indexed by resting motor threshold (MT). Results Increasing distance between the coil and underlying cortex was associated with a steep linear increase in MT. For each additional millimetre separating the stimulating coil from the scalp surface, an additional not, vert, similar2.8% of absolute stimulator output (not, vert, similar0.062 T) was required to reach MT. The gradient of the observed distance effect did not differ between hemispheres, and no differences were observed between the 50 and 70 mm TMS coils. Conclusions Coil–cortex distance directly influences the magnitude of cortical stimulation in TMS. The relationship between TMS efficacy and coil–cortex distance is well characterised by a linear function, providing a simple and effective method for scaling stimulator output to a distance adjusted MT. Significance MT measured at the scalp-surface is dependent on the underlying scalp–cortex distance, and therefore does not provide an accurate index of cortical excitability. Distance-adjusted MT provides a more accurate index of cortical excitability, and improves the safety and efficacy of MT-calibrated TMS.
Keyword Evoked potentials (Electrophysiology)
Electroencephalography
Nervous System
Q-Index Code C1

Document type: Journal Article
Sub-type: Article (original research)
Collections: Excellence in Research Australia (ERA) - Collection
School of Psychology Publications
 
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Created: Thu, 26 Feb 2009, 21:30:13 EST by Ms Karen Naughton on behalf of School of Psychology