Validation of a Double-Coil TMS Method to Assess Corticospinal Excitability Julien Grandjean, Gerard Derosiere, Pierre Vassiliadis, Louise Quemener, Ysaline de Wilde, Julie Duque Cognition and Actions Lab, Institute of Neuroscience, Université catholique de Louvain, Brussels, Belgium
www.coactionslab.com
Introduction
Conclusion
- During the two last decades, studies have used Transcranial Magnetic Stimulation (TMS) to monitor corticospinal excitability (CSE) changes in various contexts.
- Increasing TMSINTENSITY always resulted in larger MEP amplitudes. - MEPs obtained using double-coil1ms were comparable to those elicited using the standard single-coil technique, regardless of the TMSINTENSITY, the MEP side or the order of stimulation.
- Habitually, single-coil TMS is applied over one primary motor cortex (M1) eliciting motor-evoked potentials (MEPs) in the contralateral hand or limb muscle.
- The present results suggest that double-coil1ms is a reliable method to assess CSE bilaterally at rest.
- However, in many situations, it would be useful to obtain MEPs in both hands at once.
- Such a technique will allow researchers to acquire twice the amount of data in a single trial and to observe staterelated CSE changes for two hand or limb muscles at the same time.
- Such an approach requires stimulating both M1 concurrently while avoiding interference between the two stimuli and descending volleys.
- Further studies are required to verify whether this assumption holds when MEPs are elicited in other functional states.
Here, we tested the reliability of a new double-coil TMS method where the two M1 are stimulated with a 1ms inter-pulse interval (double-coil1ms).
AIM
Methods - 32 subjects were tested (16 women; 23.3 ± 1.9 years old).
L
- TMS was delivered through one (single-coil TMS) or two (doublecoil1ms TMS) small figure-of-eight coils (inner diameter = 35 mm). - TMS coils were positioned over both M1 during the whole experiment, even in the single-coil trials, as all conditions were intermingled within each block.
Double-Coil1ms
Single-Coil R
MEPsingle
- In half of the trials, single-coil TMS was used, eliciting MEPs in a single hand (MEPsingle); pulses were delivered through the coil positioned on the left or right M1, eliciting right or left hand MEPsingle in a balanced proportion.
MEPsingle
MEPdouble-1
MEPdouble-2
MEPdouble-2
MEPdouble-1
Spinal cord
- In the other half, MEPs were elicited in both hands at once using a double-coil1ms method (MEPdouble) where the two M1 are stimulated with a 1 ms inter-pulse interval. - Hence, MEPdouble could either result from a first (MEPdouble-1) or second (MEPdouble-2) pulse.
TMS pulse
0.5 mv
- MEPs were obtained at 5 different intensities of stimulation in separate blocks (TMSINTENSITY = 100%, 115%, 130%, 145% or 160% of the rMT. - 24 MEPs were obtained for each TMS condition.
AMPLIFIER
AMPLIFIER
AMPLIFIER
AMPLIFIER
TMS pulses
TMS pulse
TMS pulses
Left FDI
Left FDI
Left FDI
Left FDI
Right FDI
Right FDI
Right FDI
Right FDI
1 ms
20 ms
1 ms
Results 7 6
MEPdouble-1
MEPsingle
7
MEPdouble-2
MEP amplitude (mV)
MEP amplitude (mV)
A.
Figure A:
5 4 3 2 1 0
6 5
MEPsingle
- The grey lines represent single-subject data (n=32) for each MEPTYPE (MEPTYPE= MEPsingle, MEPdouble-1 and MEPdouble-2); the thicker coloured lines represent the mean values.
MEPdouble-1 MEPdouble-2
4
- Increasing the TMSINTENSITY by 15% always resulted in significantly larger MEP amplitudes.
3 2
- As evident on the right side figure, all MEPTYPE were comparable for each TMSINTENSITY.
1 0
100% 115% 130% 145% 160%
100% 115% 130% 145% 160%
TMS intensity (% of rMT)
TMS intensity (% of rMT)
300%
125%
+ 20%
+ 20%
200% + 4%
100%
100% - 3%
0%
- 12%
75%
-100%
- 20%
MEPdouble-2 (% of MEPsingle)
MEPdouble-1 (% of MEPsingle)
B. 300%
125% +13%
200% 100%
+ 20%
+ 5%
100% - 3%
0%
-18%
-100%
100% 115% 130% 145% 160%
100% 115% 130% 145% 160%
TMS intensity (% of rMT)
TMS intensity (% of rMT)
75%
- 20%
Figure B: - The grey lines represent single-subject data (n=32) for MEPdouble-1 (left side) and MEPdouble-2 (right side), expressed in percentage of MEPsingle; the thicker coloured lines represent the mean values for each MEPdouble type. - The mean MEPdouble-1 and MEPdouble-2 normalized values ranged from 97.8 % to 108 % and from 101 % to 102.8% of MEPsingle, respectively. - The insets display a zoom on the normalized MEPdouble data around 100%. The upper and lower lines represent the closest percentage values significantly different from normalized MEPs. - For each TMSINTENSITY, the normalized MEPdouble data were significantly different from the boundaries of a +/- 20% window centred around 100%, suggesting that they were bioequivalent to MEPsingle (Luzar-Stiffler and Stiffler, 2002).
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