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This Article Full Text Full Text (PDF) All Versions of this Article: 569/1/291    most recent jphysiol.2005.091744v1 Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via Google Scholar Google Scholar Articles by Nielsen, J. B. Articles by Hultborn, H. Search for Related Content PubMed PubMed Citation Articles by Nielsen, J. B. Articles by Hultborn, H.

¹ Division of Neurophysiology, Department of Medical Physiology, The Panum Institute, University of Copenhagen, Denmark
² Institute of Physical Exercise and Sports Science, University of Copenhagen, Nørre Allé 55, 2100 Copenhagen Ø, Denmark
³ Bioengineering Unit, University of Strathclyde, Glasgow, G4 0NW, UK
⁴ The Department of Electronics, University of York, UK
⁵ Department of Physiology, University of Oslo (Domus Medica), Oslo, Norway

The basic locomotor rhythm in the cat is generated by a neuronal network in the spinal cord. The exact organization of this network and its drive to the spinal motoneurones is unknown. The purpose of the present study was to use time (cumulant density) and frequency domain (coherence) analysis to examine the organization of the last order drive to motoneurones during fictive locomotion (evoked by application of nialamide and dihydroxyphenylalanine (DOPA)) in the spinal cat. In all cats, narrow central synchronization peaks (half-width < 3 ms) were observed in cumulants estimated between electroneurograms (ENGs) of close synergists, but not between nerves belonging to muscles acting on different joints or to antagonistic muscles. Coherence was not observed at frequencies above 100 Hz and was mainly observed between synergists. Intracellular recording was obtained from a population of 70 lumbar motoneurones. Significant short-term synchronization was observed between the individual intracellular recordings and the ENGs recorded from nerves of the same pool and of close synergists. Recordings from 34 pairs of motoneurones (10 pairs belonged to the same motor pool, 11 pairs to close synergists and 13 pairs to antagonistic pools) failed to reveal any short-lasting synchronization. These data demonstrate that short-term synchronization during fictive locomotion is relatively weak and is restricted to close synergists. In addition, coherence analysis failed to identify any specific rhythmic component in the locomotor drive that could be associated with this synchronization. These results resemble findings obtained during human treadmill walking and imply that the spinal interneurones participating in the generation of the locomotor rhythm are themselves weakly synchronized. The restricted synchronization within the locomotor drive to motoneuronal pools may be a feature of the locomotor generating networks that is related to the ability of these networks to produce highly adaptive patterns of muscle activity during locomotion.

(Received 30 May 2005; accepted after revision 8 September 2005; first published online 15 September 2005)
Corresponding author J. B. Nielsen: Division of Neurophysiology, Department of Medical Physiology, The Panum Institute, Copenhagen University, Blegdamsvej 3, 2200 Copenhagen N., Denmark. Email: j.b.nielsen{at}mfi.ku.dk