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This Article Full Text Full Text (PDF) All Versions of this Article: 582/3/1361    most recent jphysiol.2007.133199v1 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 HighWire Citing Articles via Google Scholar Google Scholar Articles by Iglesias, C. Articles by Pierrot-Deseilligny, E. Search for Related Content PubMed PubMed Citation Articles by Iglesias, C. Articles by Pierrot-Deseilligny, E. Related Collections Integrative

Caroline Iglesias^1,2, Véronique Marchand-Pauvert^1,2, George Loureno^1,2, David Burke³ and Emmanuel Pierrot-Deseilligny^1,2

¹INSERM, U731, Paris, F-75013 France ²Université Pierre et Marie Curie-Paris6, UMR S 731, Paris, F-75005 France ³Institute of Clinical Neurosciences, Royal Prince Alfred Hospital and University of Sydney, Australia

This study addresses whether there is excitation from human hand muscles to flexor carpi radialis (FCR) motoneurones mediated through propriospinal circuits and, if so, whether it is used in specific motor tasks. Electrical stimuli to the ulnar nerve at wrist level produced an excitation in FCR motoneurones with characteristics typical of a propriospinally mediated effect: low threshold (0.6 x motor threshold (MT)), a group I effect that was not reproduced by purely cutaneous stimuli, long central delay (4.1 ± 0.4 ms in single units), suppression when the stimulus intensity was increased, and facilitation of the corticospinal excitation at the premotoneuronal level. Ulnar-induced propriospinally mediated excitation was compared during selective voluntary contractions of the FCR and, at equivalent level of FCR EMG, during tasks in which the FCR was activated automatically in postural contractions rather than voluntarily (grip, pinching and pointing). The excitation was significantly greater during grip (and pinching) than during voluntary FCR contractions and pointing, whether measured in single motor units or tonic EMG activity, or whether the response to motor cortex stimulation was assessed as the compound motor-evoked potential or the corticospinal peak in single units. The discrepancy between the tasks appeared with ulnar intensities above 0.8 x MT and was then present across a wide range of stimulus intensities. This suggests a reduction in the corticospinal control of ‘feedback inhibitory interneurones’ mediating peripheral inhibition to propriospinal neurones during grip and pinching. The resulting more effective background excitation of propriospinal neurones by the peripheral input from hand muscles could contribute to stabilizing the wrist during grip.

(Received 22 March 2007; accepted after revision 17 May 2007; first published online 17 May 2007)
Corresponding author V. Marchand-Pauvert: U731 INSERM/UPMC, Physiologie et Physiopathologie de la Motricité chez l'Homme, Sce de Médecine Physique et Réadaptation, Hôpital Pitié-Salpêtrière, 47 bd de l'Hôpital, 75651 Paris cedex 13, France. Email: veronique.marchand{at}chups.jussieu.fr

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