Experimental Brain Research

, Volume 117, Issue 3, pp 472–478

Effect of contraction strength on responses in biceps brachii and adductor pollicis to transcranial magnetic stimulation

  • J. L. Taylor
  • Gabrielle M. Allen
  • Jane E. Butler
  • S. C. Gandevia
RESEARCH ARTICLE

DOI: 10.1007/s002210050243

Cite this article as:
Taylor, J., Allen, G., Butler, J. et al. Exp Brain Res (1997) 117: 472. doi:10.1007/s002210050243

Abstract 

The sizes of the motor-evoked potentials (MEPs) and the durations of the silent periods after transcranial magnetic stimulation were examined in biceps brachii, brachioradialis and adductor pollicis in human subjects. Stimuli of a wide range of intensities were given during voluntary contractions producing 0–75% of maximal force (maximal voluntary contraction, MVC). In adductor pollicis, MEPs increased in size with stimulus intensity and with weak voluntary contractions (5% MVC), but did not grow larger with stronger contractions. In the elbow flexors, MEPs grew little with stimulus intensity, but increased in size with contractions of up to 50% of maximal. In contrast, the duration of the silent period showed similar changes in the three muscles. In each muscle it increased with stimulus intensity but was unaffected by changes in contraction strength. Comparison of the responses evoked in biceps brachii by focal stimulation over the contralateral motor cortex with those evoked by stimulation with a round magnetic coil over the vertex suggests an excitatory contribution from the ipsilateral cortex during strong voluntary contractions.

Key words Transcranial magnetic stimulation Motor cortex Motor-evoked potentials Silent period Human 

Copyright information

© Springer-Verlag Berlin Heidelberg 1997

Authors and Affiliations

  • J. L. Taylor
    • 1
  • Gabrielle M. Allen
    • 1
  • Jane E. Butler
    • 1
  • S. C. Gandevia
    • 1
  1. 1.Prince of Wales Medical Research Institute, High St, Randwick, 2031, Australia Fax: +61-2382-2724, e-mail: jl.taylor@unsw.edu.auAU

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