Intra- and interindividual variability of motor responses to repetitive transcranial magnetic stimulation.
OBJECTIVE
Repetitive transcranial magnetic stimulation (rTMS) can modify cortical excitability and is widely used for clinical and research purposes. We sought to determine the intra- and interindividual variability of its effects on motor cortex excitability, and whether repeated paired-pulses yield less variability than repeated single-pulses.


METHODS
We investigated rTMS over the left motor cortex of 6 healthy subjects and recorded motor evoked potentials (MEPs) from the right abductor digiti minimi muscle. Eighty single suprathreshold stimuli or conditioning-test pairs of stimuli were delivered at 2Hz frequency. The pairs consisted of a subthreshold pulse followed by a suprathreshold pulse after 2, 5 or 10ms. In each subject we studied all types of rTMS 5 times on separate days. Single suprathreshold pulses at 0.17Hz preceded rTMS for baseline determination.


RESULTS
The day-to-day variability of MEPs during either type of rTMS was small compared to the subject-to-subject variability. MEPs increased during all types of rTMS except for interstimulus interval (ISI) 2ms. Paired-pulses yielded less variability than single-pulse rTMS.


CONCLUSIONS
Motor responses to rTMS show a high interindividual, but a low intraindividual variability. Repeated paired-pulses yield less variability than repeated single-pulses.
Sommer
M
M
Department of Clinical Neurophysiology, University of Goettingen, P.O. Box 3742, D-37070, Goettingen, Germany.
Wu
T
T
Tergau
F
F
Paulus
W
W
D000328:Adult; D000704:Analysis of Variance; D004558:Electric Stimulation; D019054:Evoked Potentials, Motor / Q000502:physiology*; D006801:Humans; D009044:Motor Cortex / Q000502:physiology*; D011712:Pyramidal Tracts / Q000502:physiology*; D050781:Transcranial Magnetic Stimulation