Modulation of intracortical facilitatory circuits of the human primary motor cortex by digital nerve stimulation

Exp Brain Res. 2007 Jan;176(3):425-31. doi: 10.1007/s00221-006-0624-2. Epub 2006 Sep 2.

Abstract

We investigated the effect of electrical digit stimulation on two different intracortical facilitatory phenomena. Paired-pulse transcranial magnetic stimuli (TMS) with different conditioning stimulus (CS) intensities were applied over the primary motor cortex (M1). Electromyographic (EMG) recordings were made from the relaxed right abductor digiti minimi muscle (ADM). The effect of preceding sensory stimulation applied to the ipsilateral digit V on the conditioning magnetic stimulus was examined. Changing the CS intensity affected the influence of peripheral electrical stimulation on motor evoked potential (MEP) amplitudes evoked by paired pulse TMS. Inhibition induced by ipsilateral digit stimulation was strongest with the lowest CS intensity if MEP amplitudes were evoked by a subthreshold CS followed by a suprathreshold test stimulus (TS) at an interstimulus interval (ISI) of 10 ms. In contrast, inhibition induced by digit stimulation in a paired-pulse paradigm with a suprathreshold first and a subthreshold second stimulus at ISI of 1.5 ms was strongest with the highest CS intensity. These findings suggest that appropriately timed peripheral electrical stimuli differentially modulate facilitatory interactions in the primary motor cortex. They further support the hypothesis that intracortical facilitation (ICF) and short-interval intracortical facilitation (SICF) are evoked through different mechanisms.

MeSH terms

  • Abducens Nerve / physiology*
  • Abducens Nerve / radiation effects
  • Adult
  • Analysis of Variance
  • Dose-Response Relationship, Radiation
  • Electric Stimulation / methods
  • Electromyography / methods
  • Evoked Potentials, Motor / physiology*
  • Evoked Potentials, Motor / radiation effects
  • Female
  • Fingers / innervation*
  • Fingers / physiology
  • Humans
  • Male
  • Motor Cortex / physiology*
  • Neural Inhibition / physiology
  • Neural Inhibition / radiation effects
  • Reaction Time / physiology
  • Reaction Time / radiation effects
  • Sensory Thresholds / physiology
  • Sensory Thresholds / radiation effects
  • Time Factors
  • Transcranial Magnetic Stimulation / methods