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J Neurophysiol 101: 31-41, 2009. First published November 19, 2008; doi:10.1152/jn.90362.2008
0022-3077/09 $8.00

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Circuits Generating Corticomuscular Coherence Investigated Using a Biophysically Based Computational Model. I. Descending Systems

Institute of Neuroscience, Newcastle University, Henry Wellcome Building, Newcastle upon Tyne, United Kingdom

Submitted 13 March 2008; accepted in final form 11 November 2008

Recordings of motor cortical activity typically show oscillations around 10 and 20 Hz; only those at 20 Hz are coherent with electromyograms (EMGs) of contralateral muscles. Experimental measurements of the phase difference between approximately 20-Hz oscillations in cortex and muscle are often difficult to reconcile with the known corticomuscular conduction delays. We investigated the generation of corticomuscular coherence further using a biophysically based computational model, which included a pool of motoneurons connected to motor units that generated EMGs. Delays estimated from the coherence phase–frequency relationship were sensitive to the width of the motor unit action potentials. In addition, the nonlinear properties of the motoneurons could produce complex, oscillatory phase–frequency relationships. This was due to the interaction of cortical inputs to the motoneuron pool with the intrinsic rhythmicity of the motoneurons; the response appeared more linear if the firing rate of motoneurons varied widely across the pool, such as during a strong contraction. The model was able to reproduce the smaller than expected delays between cortex and muscles seen in experiments. However, the model could not reproduce the constant phase over a frequency band sometimes seen in experiments, nor the lack of around 10-Hz coherence. Simple propagation of oscillations from cortex to muscle thus cannot completely explain the observed corticomuscular coherence.

This article has been cited by other articles:

				E. R. Williams, D. S. Soteropoulos, and S. N. Baker Coherence Between Motor Cortical Activity and Peripheral Discontinuities During Slow Finger Movements J Neurophysiol, August 1, 2009; 102(2): 1296 - 1309. [Abstract] [Full Text] [PDF]

				E. R. Williams and S. N. Baker Renshaw Cell Recurrent Inhibition Improves Physiological Tremor by Reducing Corticomuscular Coupling at 10 Hz J. Neurosci., May 20, 2009; 29(20): 6616 - 6624. [Abstract] [Full Text] [PDF]