Modulation of corticomotor excitability by an I-wave intervention delivered during low-level voluntary contraction.
Transcranial magnetic stimulation (TMS) interventions that modulate cortical plasticity may achieve a more functional benefit if combined with neuro-rehabilitation therapies. With a TMS protocol targeting I-wave dynamics, it is possible to deliver stimuli while a subject performs a motor task, and this may more effectively target functional networks related to the task. However, the efficacy of this intervention during a simple task such as a low-level voluntary contraction is not known. We delivered paired-pulse TMS at an inter-pulse interval (IPI) of 1.5 ms for 15 min while subjects performed a 10 ± 2.5% voluntary contraction of the first dorsal interosseous (FDI) muscle and made motor evoked potential (MEP) amplitude and short-interval intracortical facilitation (SICF) curve measurements. Pre-intervention SICF curves showed only a single peak at 1.3-1.5 ms IPI. During the intervention, MEP amplitude steadily increased (P < 0.001) to 137 ± 13% of its initial value. After the intervention, SICF curves were increased in amplitude (P < 0.001) and later peaks emerged at 2.8 and 4.3 ms IPIs. A control experiment, replacing paired-pulse stimulation with single-pulse stimulation showed no effect on MEP amplitude (P = 0.951). We conclude that the I-wave intervention can be administered concurrently with a simple motor task and that it acts by increasing trans-synaptic efficacy across a number of I-waves. The ability to perform a motor task simultaneously with a TMS intervention could confer a degree of specificity to the induced excitability changes and may be beneficial for functional neuro-rehabilitation programs built around motor learning and retraining.
Centre for Neuromuscular and Neurological Disorders, M518, University of Western Australia, Nedlands, WA 6009, Australia.
B I
BI
Silbert
J T
JT
Gibbons
R H F
RH
Cash
F L
FL
Mastaglia
G W
GW
Thickbroom
D000293:Adolescent; D000328:Adult; D004558:Electric Stimulation / Q000379:methods; D019054:Evoked Potentials, Motor / Q000502:physiology; D005260:Female; D006801:Humans; D008297:Male; D009119:Muscle Contraction / Q000502:physiology*; D018482:Muscle, Skeletal / Q000502:physiology*; D011930:Reaction Time / Q000502:physiology; D013997:Time Factors; D050781:Transcranial Magnetic Stimulation / Q000379:methods; D055815:Young Adult