Task-dependent facilitation of motor evoked potentials during dynamic and steady muscle contractions

Zsuzsanna Arányi, Johannes Mathis, Christian W. Hess, Kai M. Rösler

Research output: Contribution to journalArticle

35 Citations (Scopus)

Abstract

Task-dependent differences in the facilitation of motor evoked potentials (MEPs) following cortex stimulation were studied in a proximal (deltoid) and a distal muscle (abductor digiti minimi; ADM) in 23 healthy subjects during both dynamic and steady contractions of the target muscle under isometric and under nonisometric conditions. In the deltoid, MEP amplitudes were significantly greater if stimulation was performed during dynamic contractions than during steady contractions, despite equal background electromyographic levels just prior to the stimulus. The same task-specific extra facilitation of deltoid MEP amplitudes was also found with magnetic stimulation of the brain stem instead of the cortex in 3 subjects. In the ADM, no such task-dependent extra facilitation of MEPs during dynamic contractions was found. It is concluded that in the deltoid, during dynamic contractions, a greater proportion of the spinal motoneurons is close to depolarization threshold (greater 'subliminal fringe') whereas the number of firing motoneurons is similar to that during steady contraction. The lack of task-dependent extra facilitation of MEPs in the ADM is explained by the predominant recruitment principle for force gradation in small hand muscles, which is in contrast to the predominant frequency principle used in proximal muscles.

Original languageEnglish
Pages (from-to)1309-1316
Number of pages8
JournalMuscle and Nerve
Volume21
Issue number10
DOIs
Publication statusPublished - Jan 1 1998

Keywords

  • Facilitation
  • Motor evoked potential
  • Task dependency

ASJC Scopus subject areas

  • Physiology
  • Clinical Neurology
  • Cellular and Molecular Neuroscience
  • Physiology (medical)

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