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NEUROSCIENCE |
1 Human Cortical Physiology Section
5 Human Motor Control Section, National Institutes of Health, National Institute of Neurological Disorders & Stroke, Bethesda, MD 20892, USA
2
INSERM, UMRS 731, Paris, F-75651, France
3
Université Pierre et Marie Curie Paris 6, UMRS 731, Paris, F-75013, France
4
Physical Medicine and Rehabilitation, St Vincent Hospital, Catholic University of Korea, Paldal-gu, Suwon, Republic of Korea 442-723
6
Sezione di Neurofisiologia Clinica, Dipartimento di Scienze Neurologiche e del Comportamento, Universitá di Siena, I-53100 Siena, Italy
The spinal cord is able to express use-dependent plasticity, as demonstrated in spinalized cats following treadmill training. In humans, spinal use-dependent plasticity is inferred from modifications in the size of H reflex, which are often more prominent after skilled motor training. Plasticity can develop at synaptic connections between afferent fibres and/or descending tracts and motoneurones or interneurones interposed in the spinal pathways. Here we explore whether skilled training induces a change in synaptic efficacy at the synapse between Ia afferents and soleus (Sol) motoneurones. Synaptic efficacy can be modulated presynaptically through changes of the probability of transmitter release (homosynaptic depression, HD). The frequency-related depression of the Sol H reflex, thought to reflect HD, was tested at rest, before and after one single skilled (14 subjects) or non-skilled (9 subjects) cycling training session. Performance improved in both groups but to a larger extent with skilled training, while HD increased immediately after and the day following skilled training in the absence of changes with non-skilled training. These results support the view that spinal cord function is able to encode a local motor memory.
(Received 16 October 2006;
accepted after revision 8 December 2006;
first published online 14 December 2006)
Corresponding author S. Meunier: INSERM U731, UPMC, Médecine Physique et Réadaptation, Hopital La Salpêtrière, 47 Bd de l'Hopital, 75651 Paris cedex 13, France. Email: meunier.sabine{at}free.fr
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