The relationship between peripheral and early cortical activation induced by transcranial magnetic stimulation

  • Maki H
  • Ilmoniemi R
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The purpose of this study was to assess the relationship between peripheral
muscle responses (motor evoked potentials, MEP) evoked by transcranial
magnetic stimulation (TMS) and the early components of the TMS-evoked
EEG response, both of which reflect cortical excitability. Left primary
motor cortex of five healthy volunteers was stimulated with 100%
of the motor threshold. The relationship between MEP amplitudes and
the peak-to-peak amplitudes of the N15-P30 complex of the evoked
EEG signal was determined at the single-trial level. MEP and N15-P30
amplitudes were significantly correlated in all five subjects. The
results support the view that the amount of direct activation of
neurons in M1 evoked by TMS affects both subsequent cortical activation
and the activation of the target muscle. Cortical excitability is
altered in some neuronal disorders and modulated locally during various
tasks. It could thus be used as a marker of the state of health in
many cases and as a method to study brain function. The present results
improve our understanding of the early components of the TMS-evoked
EEG signal, which reflect cortical excitability, and may thus have
widespread use in clinical and scientific studies.

Author-supplied keywords

  • Electroencephalography; Evoked Potentials
  • Motor; Female; Hand; Humans; Male; Motor Cortex/p
  • Skeletal/innervation/physiology; Neurons/physiolo

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  • H Maki

  • R J Ilmoniemi

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