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J Physiol Volume 586, Number 5, 1239-1245, March 1, 2008 DOI: 10.1113/jphysiol.2007.146605
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SYMPOSIUM REPORT

Muscle synergies during locomotion in the cat: a model for motor cortex control

 Trevor Drew1,2, John Kalaska1,2 and Nedialko Krouchev2

1 Groupe de Recherche sur le Système Nerveux Centrale (GRSNC)
2 Département de physiologie, Université de Montréal, CP 6128, Succ. ‘centre-ville’, Montréal, Québec, H3C 3J7, Canada

It is well established that the motor cortex makes an important contribution to the control of visually guided gait modifications, such as those required to step over an obstacle. However, it is less clear how the descending cortical signal interacts with the interneuronal networks in the spinal cord to ensure that precise changes in limb trajectory are appropriately incorporated into the base locomotor rhythm. Here we suggest that subpopulations of motor cortical neurones, active sequentially during the step cycle, may regulate the activity of small groups of synergistic muscles, likewise active sequentially throughout the step cycle. These synergies, identified by a novel associative cluster analysis, are defined by periods of muscle activity that are coextensive with respect to the onset and offset of the EMG activity. Moreover, the synergies are sparse and are frequently composed of muscles acting around more than one joint. During gait modifications, we suggest that subpopulations of motor cortical neurones may modify the magnitude and phase of the EMG activity of all muscles contained within a given synergy. Different limb trajectories would be produced by differentially modifying the activity in each synergy thus providing a flexible substrate for the control of intralimb coordination during locomotion.

(Received 14 October 2007; accepted after revision 15 January 2008; first published online 17 January 2008)
Corresponding author T. Drew: Département de physiologie, Université de Montréal, C.P. 6128, Succ. ‘centre-ville’, Montréal, Québec, H3C 3J7, Canada. Email: trevor.drew{at}umontreal.ca

This report was presented at The Journal of Physiology Symposium on The cortex, interneurones and motoneurones in the control of movement, IBRO World Congress of Neuroscience, Darwin, Australia, 19 July 2007. It was commissioned by the Editorial Board and reflects the views of the authors.




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R. C. Fitzpatrick
The cortex, interneurones and motoneurones in the control of movement
J. Physiol., March 1, 2008; 586(5): 1215 - 1216.
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