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This Article Full Text Full Text (PDF) All Versions of this Article: 586/4/1017    most recent jphysiol.2007.145318v1 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 Google Scholar Articles by Duclos, Y. Articles by Rossi-Durand, C. PubMed PubMed Citation Articles by Duclos, Y. Articles by Rossi-Durand, C. Related Collections Neuroscience

¹ Laboratoire de Plasticité et Physio-Pathologie de la Motricité (P3M), UMR 6196, Aix-Marseille Université/CNRS, Marseille, France
² Laboratoire de Neurobiologie de la Cognition (LNC), UMR 6155, Aix-Marseille Université/CNRS, Marseille, France

The influence of motor preparation on human motoneuron activity was studied by combining single motor unit recording techniques with reaction-time (RT) methods. The tonic activity of wrist extensor motor units associated with voluntary isometric contractions was analysed during preparation for a ballistic wrist extensor muscle contraction, using a time preparation procedure. Two durations of the preparatory period elapsing between the warning signal and the response signal were used in separate blocks of trials: a short preparatory period (1 s) allowing optimum time preparation, and a longer, non-optimum one (3 s). Changes in motoneuron tonic discharge patterns not associated with any changes in the force output were observed during the preparatory period, which suggests that these changes were subtle enough to prevent any changes in muscle contraction from occurring before the forthcoming movement. The changes observed were a lengthening of the mean interspike interval (ISI) and a decrease in the ISI variability. These data confirm that inhibitory mechanisms are activated during motor preparation and suggest that spinal inhibitory mechanisms are involved in the preparatory processes. The mechanisms possibly involved, such as presynaptic inhibition, dysfacilitation processes or AHP conductance changes, are discussed. The fact that the preparation-induced effects on motoneuron activity were particularly prominent during the last part of the 3 s preparatory period suggests that they were probably related to the neural processes underlying temporal estimation. The anticipatory changes in motoneuron activity observed here during preparation for action provide evidence that central influences act on spinal motoneurons well before it is time to act.

(Received 21 September 2007; accepted after revision 6 December 2007; first published online 13 December 2007)
Corresponding author C. Rossi-Durand: Laboratoire de Plasticité et PhysioPathologie de la Motricité (P3M), Unité Mixte de Recherche 6196, Aix-Marseille Université/CNRS, 31, chemin Joseph-Aiguier, 13402 Marseille cedex 20, France. Email: crd{at}dpm.cnrs-mrs.fr