Modulation of spinal cord excitability by subthreshold repetitive transcranial magnetic stimulation of the primary motor cortex in humans.
Repetitive transcranial magnetic stimulation (rTMS) allows the modulation of intra-cortical excitability and may therefore affect the descending control of spinal excitability. We applied rTMS at subthreshold intensity and 1 Hz frequency for 10 min to the left primary motor cortex representation of the flexor carpi radialis muscle (FCR) in 10 subjects and assessed the H and M responses to median nerve stimulation before and after the rTMS. Following rTMS, H wave thresholds significantly reduced by approximately 20%. Maximal H but not M wave amplitude significantly increased over the baseline, so that H/M amplitude ratio was increased by 41%. Sham stimulation did not induce any noticeable change in M or H waves. Slow rTMS might facilitate monosynaptic spinal cord reflexes by inhibiting the cortico-spinal projections modulating spinal excitability.
Valero-Cabré
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A
Laboratory for Magnetic Brain Stimulation, Department of Neurology, Beth Israel Deaconess Medical Center, Harvard Medical School, Boston, MA 02215, USA.
Oliveri
M
M
Gangitano
M
M
Pascual-Leone
A
A
D000328:Adult; D004599:Electric Stimulation Therapy / Q000379:methods*; D004576:Electromyography; D006801:Humans; D008297:Male; D008564:Membrane Potentials / Q000502:physiology; D009044:Motor Cortex / Q000502:physiology*; D009069:Movement Disorders / Q000503:physiopathology / Q000628:therapy; D009119:Muscle Contraction / Q000502:physiology; D009128:Muscle Spasticity / Q000503:physiopathology / Q000628:therapy; D018482:Muscle, Skeletal / Q000294:innervation / Q000502:physiology; D009431:Neural Conduction / Q000502:physiology; D009474:Neurons / Q000502:physiology*; D011712:Pyramidal Tracts / Q000502:physiology*; D011930:Reaction Time / Q000502:physiology; D012023:Reflex, Monosynaptic / Q000502:physiology*; D013116:Spinal Cord / Q000502:physiology*; D050781:Transcranial Magnetic Stimulation