Neuroscience 2001 Abstract
| Presentation Number: | 401.13 |
|---|---|
| Abstract Title: | Motor cortex excitability contributes to motor responses elicited by transcranial magnetic stimulation. |
| Authors: |
Gagne, M.*1
; Schneider, C.1
; Devanne, H.1
; Zehrouni, F.1
; Capaday, C.1
1Centre de Recherche Universite Laval Robert-Giffard, Laval University, Beauport, Canada |
| Primary Theme and Topics |
Motor Systems - Cortex and Thalamus -- Physiology |
| Session: |
401. Cortex and thalamus: cortical excitability Poster |
| Presentation Time: | Monday, November 12, 2001 1:00 PM-2:00 PM |
| Location: | Exhibit Hall EE-10 |
| Keywords: | EMG, Evoked potentials, Motor control, Neuroimaging |
The purpose of this study was to determine which cerebral structures are activated by transcranial magnetic stimulation (TMS). To this end, we measured the effective depth (ED) of TMS, defined as the maximal distance from coil to scalp at which a motor response could be evoked. These physiological measurements were correlated with anatomical measurements obtained by magnetic resonance imaging (MRI). Motor evoked potentials (MEPs) were recorded by EMG from the first dorsal interosseus (FDI) muscle. Two intensities of stimulation (1.1 x Motor Threshold (MT) and 2 x MT) and two levels of contraction (at rest and 10% of maximal voluntary contraction, MVC) were tested with two different sized figure-of-eight coils. At rest, the ED at 1.1 x MT was 3 ± 1 mm and 6 ± 2 mm, with the small and the big coil respectively. With a stimulus of 2 x MT, the EDs increased to 12 ± 1 mm and 19 ± 3 mm. Remarkably, for all stimulus intensities the ED increased when the FDI was voluntarily activated. For example, stimulation with the big coil at 2 x MT during a contraction of 10% MVC increased the ED from 19 mm to 29 mm. The anatomical distance measured between scalp and cortex from MRIs was about 11 mm and the thickness of grey matter about 5 mm. These results suggest that the white matter is directly activated at high TMS intensities. Finally, increased motor cortex excitability during voluntary contraction of the FDI is likely the cause of the increased ED. This also strongly suggests that motor cortex excitability contributes significantly to the size of MEPs.
Supported by Canadian Institutes of Health Research
Sample Citation:
[Authors]. [Abstract Title]. Program No. XXX.XX. 2001 Neuroscience Meeting Planner. San Diego, CA: Society for Neuroscience, 2001. Online.
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