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J Physiol Volume 579, Number 2, 389-402, March 1, 2007 DOI: 10.1113/jphysiol.2006.123174
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NEUROSCIENCE

Changes in EMG coherence between long and short thumb abductor muscles during human development

 Simon F. Farmer1,2,3, John Gibbs3, David M. Halliday4, Linda M. Harrison3, Leon M. James2,3, Margaret J. Mayston3 and John A. Stephens3

1 Institute of Neurology and National Hospital for Neurology and Neurosurgery, Queen Square, London WC1N 3BG, UK
2 Departments of Clinical Neurology and Neurophysiology, St Mary's NHS Trust, London W2 1NY, UK
3 Department of Physiology, University College London, Gower Street, London WC1E 6BT, UK
4 Department of Electronics, University of York, York YO10 5DD, UK

In adults, motoneurone pools of synergistic muscles that act around a common joint share a common presynaptic drive. Common drive can be revealed by both time domain and frequency domain analysis of EMG signals. Analysis in the frequency domain reveals significant coherence in the range 1–45 Hz, with maximal coherence in low (1–12 Hz) and high (16–32 Hz) ranges. The high-frequency range depends on cortical drive to motoneurones and is coherent with cortical oscillations at ~20 Hz frequencies. It is of interest to know whether oscillatory drive to human motoneurone pools changes with development. In the present study we examined age-related changes in coherence between rectified surface EMG signals recorded from the short and long thumb abductor muscles during steady isometric contraction obtained while subjects abducted the thumb against a manipulandum. We analysed EMG data from 36 subjects aged between 4 and 14 years, and 11 adult subjects aged between 22 and 59 years. Using the techniques of pooled coherence analysis and the {chi}2 difference of coherence test we demonstrate that between the ages of 7 and 9 years, and 12 and 14 years, there are marked increases in the prevalence and magnitude of coherence at frequencies between 11 and 45 Hz. The data from subjects aged 12–14 years were similar to those obtained from adult controls. The most significant differences between younger children and the older age groups were detected at frequencies close to 20 Hz. We believe that these are the first reported results demonstrating significant late maturational changes in the ~20 Hz common oscillatory drive to human motoneurone pools.

(Received 24 October 2006; accepted after revision 14 December 2006; first published online 21 December 2006)
Corresponding author S. F. Farmer: Institute of Neurology and National Hospital for Neurology and Neurosurgery, Queen Square, London WC1N 3BG, UK. Email: s.farmer{at}ion.ucl.ac.uk






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