Repetitive paired-pulse TMS at I-wave periodicity markedly increases corticospinal excitability: a new technique for modulating synaptic plasticity.
OBJECTIVE
We hypothesised that facilitatory I-wave interaction set up by paired-pulse transcranial magnetic stimulation delivered with I-wave periodicity (iTMS) may reinforce trans-synaptic events and provide a means for modulating synaptic plasticity and cortical excitability. Our objective was to determine whether prolonged iTMS can increase corticospinal excitability, and whether this form of stimulation can have lasting aftereffects.


METHODS
Paired stimuli of equal strength with a 1.5 ms inter-stimulus interval were delivered for 30 min at a rate of 0.2 Hz. Motor threshold and motor evoked potential (MEP) amplitude to single-pulse TMS was compared before and after intervention.


RESULTS
Paired-pulse MEP amplitude increased linearly throughout the period of iTMS, and had increased five-fold by the end of the stimulation period. Single-pulse MEP amplitude was increased a mean of four-fold for 10 min after stimulation. Motor threshold was unaffected.


CONCLUSIONS
iTMS is an effective method for increasing excitability of the human motor cortex, and probably acts by increasing synaptic efficacy.


CONCLUSIONS
Reinforcement of trans-synaptic events by iTMS may provide a means to investigate and modulate synaptic plasticity in the brain.
Thickbroom
Gary W
GW
Centre for Neuromuscular and Neurological Disorders, Queen Elizabeth II Medical Centre, University of Western Australia, Perth, Nedlands, WA 6009, Australia. gthickbr@cyllene.uwa.edu.au
Byrnes
Michelle L
ML
Edwards
Dylan J
DJ
Mastaglia
Frank L
FL
D000328:Adult; D004056:Differential Threshold / Q000528:radiation effects; D004307:Dose-Response Relationship, Radiation; D004576:Electromyography / Q000379:methods; D019054:Evoked Potentials, Motor / Q000502:physiology / Q000528:radiation effects; D005260:Female; D006801:Humans; D008297:Male; D009044:Motor Cortex / Q000502:physiology / Q000528:radiation effects*; D018482:Muscle, Skeletal / Q000502:physiology; D009433:Neural Inhibition / Q000502:physiology / Q000528:radiation effects*; D009473:Neuronal Plasticity / Q000528:radiation effects*; D010507:Periodicity; D011712:Pyramidal Tracts / Q000502:physiology / Q000528:radiation effects*; D011930:Reaction Time / Q000502:physiology / Q000528:radiation effects; D013997:Time Factors; D050781:Transcranial Magnetic Stimulation