Simple metric for scaling motor threshold based on scalp-cortex distance: Application to studies using transcranial magnetic stimulation

Stokes, MG, Chambers, CD, Gould, IC, Henderson, TR, Janko, NE, Allen, NB and Mattingley, JB (2005) Simple metric for scaling motor threshold based on scalp-cortex distance: Application to studies using transcranial magnetic stimulation. Journal of Neurophysiology, 94 6: 4520-4527. doi:10.1152/jn.00067.2005


Author Stokes, MG
Chambers, CD
Gould, IC
Henderson, TR
Janko, NE
Allen, NB
Mattingley, JB
Title Simple metric for scaling motor threshold based on scalp-cortex distance: Application to studies using transcranial magnetic stimulation
Journal name Journal of Neurophysiology   Check publisher's open access policy
ISSN 0022-3077
Publication date 2005-01-01
Sub-type Article (original research)
DOI 10.1152/jn.00067.2005
Volume 94
Issue 6
Start page 4520
End page 4527
Total pages 8
Place of publication Bethesda
Publisher Amer Physiological Soc
Language eng
Abstract Stokes, Mark G., Christopher D. Chambers, Ian C. Gould, Tracy R. Henderson, Natasha E. Janko, Nicholas B. Allen, and Jason B. Mattingley. Simple metric for scaling motor threshold based on scalp-cortex distance: application to studies using transcranial magnetic stimulation. J Neurophysiol 94:4520-4527,2005. First published August 31,2005;doi:10.1152/jn.00067.2005. Transcranial magnetic stimulation (TMS) is a unique method in neuroscience used to stimulate focal regions of the human brain. As TMS gains popularity in experimental and clinical domains, techniques for controlling the extent of brain stimulation are becoming increasingly important. At present, TMS intensity is typically calibrated to the excitability of the human motor cortex, a measure referred to as motor threshold (MT). Although TMS is commonly applied to nonmotor regions, most applications do not consider the effect of changes in distance between the stimulating device and underlying neural tissue. Here we show that for every millimeter from the stimulating coil, an additional 3% of TMS output is required to induce an equivalent level of brain stimulation at the motor cortex. This abrupt spatial gradient will have crucial consequences when TMS is applied to nonmotor regions because of substantial variance in scalp-cortex distances over different regions of the head. Stimulation protocols that do not account for cortical distance therefore risk substantial under-or overstimulation. We describe a simple method for adjusting MT to account for variations in cortical distance, thus providing a more accurate calibration than unadjusted MT for the safe and effective application of TMS in clinical and experimental neuroscience.
Keyword Neurosciences
Physiology
Cortical Excitability
Phosphene Thresholds
Spatial Attention
Brain
Coil
Frequency
Safety
Adults
Age
Q-Index Code C1

Document type: Journal Article
Sub-type: Article (original research)
Collections: Excellence in Research Australia (ERA) - Collection
Queensland Brain Institute Publications
 
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