Experimental Brain Research

, Volume 122, Issue 4, pp 433–440

Covariation between human intrinsic hand muscles of the silent periods and compound muscle action potentials evoked by magnetic brain stimulation: evidence for common inhibitory connections

  • King-Hee Ho
  • Kannan Nithi
  • K. R. Mills
RESEARCH ARTICLE

DOI: 10.1007/s002210050531

Cite this article as:
Ho, KH., Nithi, K. & Mills, K. Exp Brain Res (1998) 122: 433. doi:10.1007/s002210050531

Abstract 

Transcranial magnetic stimuli at different stimulus intensities were applied in six healthy subjects to test the hypothesis that, in different intrinsic hand muscles, the duration of the resultant cortically evoked silent periods (C-SPs) from each stimulus would be positively correlated between muscles, indicating a common inhibitory mechanism. A figure-of-eight coil discharging through a Magstim 200 stimulator delivered 25 stimuli at each stimulus intensity at a minimum of five intensities ranging from 55% to 160% of the individual resting motor threshold. In each subject, simultaneous surface recordings from pairs of muscles were made from the first dorsal interosseous (FDI), opponents pollicis (OP), abductor pollicis brevis (APB) and abductor digiti minimi (ADM). The C-SP durations within all three muscle pairs tested were highly correlated (P<0.001). The amplitude of the preceding compound-muscle action potentials (CMAPs) was positively correlated between FDI and OP, but not between APB and ADM or FDI and ADM. C-SP duration was linearly related to stimulus intensity, but did not correlate with the latency or amplitude of the preceding CMAP. SPs elicited by peripheral nerve stimuli in pairs of hand muscles did not co-vary significantly. The results provide evidence that inhibitory influences of cortical origin are distributed widely to intrinsic hand muscles. In contrast, covariation of excitatory effects only appears between muscles synergistically involved in a motor task.

Key words Magnetic brain stimulationSilent periodHand musclesCommon connections

Copyright information

© Springer-Verlag Berlin Heidelberg 1998

Authors and Affiliations

  • King-Hee Ho
    • 1
  • Kannan Nithi
    • 1
  • K. R. Mills
    • 1
  1. 1.Clinical Neurophysiology Unit, University Department of Neurology, The Radcliffe Infirmary, Woodstock Road, Oxford OX2 6HE, UK e-mail: kerry.mills@clinical-neurology.ox.ac.uk, Fax: 44-1865-790493GB