Inter- and intra-individual variability of paired-pulse curves with transcranial magnetic stimulation (TMS).
OBJECTIVE
Previous studies have evaluated the variability of motor thresholds (MTs) and amplitude of motor-evoked potentials (MEPs) to transcranial magnetic stimulation (TMS) within and across individuals. Here we evaluate the reproducibility and inter-hemispheric variability of measures of cortical excitability using the 'conventional' paired-pulse (PP) TMS technique.


METHODS
We studied PP curves of the left and right hemisphere in 10 healthy subjects on two separate days 2 weeks apart. The inter-stimulus intervals studied were 1, 3, 6, 8, 10 and 12 ms with the conditioning stimulus being 80% of the resting MT, and a single test stimulus producing MEPs of approximately 0.8 mV peak-to-peak amplitude.


RESULTS
As a group, the PP curves of the left and right hemispheres, and of Day 1 and Day 2 were not significantly different. The intracortical inhibition (ICI), but not the intracortical facilitation, showed a good correlation across days within the individuals.


CONCLUSIONS
Cortical excitability, particularly ICI, measured by PP TMS shows no inter-hemispheric asymmetry and is reproducible within individuals.
Maeda
Fumiko
F
Laboratory for Magnetic Brain Stimulation, Department of Neurology, Beth Israel Deaconess Medical Center, Harvard Medical School, Kirstein Building KS 454, 330 Brookline Avenue, Boston MA, USA.
Gangitano
Massimo
M
Thall
Mark
M
Pascual-Leone
Alvaro
A
D000328:Adult; D004292:Dominance, Cerebral / Q000502:physiology; D004558:Electric Stimulation / Q000295:instrumentation / Q000379:methods; D004574:Electromagnetic Fields; D019054:Evoked Potentials, Motor / Q000502:physiology; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D009044:Motor Cortex / Q000502:physiology*; D015588:Observer Variation; D015203:Reproducibility of Results; D012684:Sensory Thresholds / Q000502:physiology; D013997:Time Factors