The influence of changes in the intensity of magnetic stimulation on coil output.
We measured the peak voltage induced in a sensing loop by a Magstim 200 magnetic stimulator. Coil output varied little for repeated stimulation at the same intensity over a wide range of coil output. In contrast, the first stimulus immediately after a change in intensity was of larger amplitude and showed greater variability than subsequent stimuli. The effect was seen for changes in intensity of 5% and 60% and was greater for reductions than for increases in stimulation intensity. Stimulation immediately after a reduction in intensity from 100% to 40% resulted in peak induced voltages as high as those recorded for repeated stimulation at 43% of maximum coil output. Increased coil output following changes in stimulation intensity may affect measurement of the threshold old for motor cortical stimulation. The effect of a change in intensity could be minimized by delaying stimulation for at least 30 s or discarding the first stimulus after the change.
Reutens
D C
DC
Department of Neurology, Austin Hospital, Heidelberg, Victoria, Australia.
MacDonell
R A
RA
Berkovic
S F
SF
D001921:Brain / Q000502:physiology*; D005071:Evoked Potentials / Q000502:physiology*; D006801:Humans; D008280:Magnetics; D009046:Motor Neurons / Q000502:physiology*; D009132:Muscles / Q000294:innervation*