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This Article Full Text Full Text (PDF) All Versions of this Article: 570/1/113    most recent jphysiol.2005.095240v1 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 Baken, B. C. M. Articles by Duysens, J. Search for Related Content PubMed PubMed Citation Articles by Baken, B. C. M. Articles by Duysens, J. Related Collections Neuroscience

¹ Radboud University Nijmegen Medical Center, Department of Rehabilitation Medicine, Nijmegen, The Netherlands
² Sint Maartenskliniek, SMK-Research, Nijmegen, The Netherlands
³ Radboud University Nijmegen, Nijmegen Institute for Cognition and Information, Nijmegen, The Netherlands
⁴ University Hospital Balgrist, Spinal Cord Injury Center, Zurich, Switzerland

Abstract

Reflex responses are often less pronounced when they are self-induced, but this question has barely been investigated quantitatively. The issue is particularly relevant for locomotion since it has been shown that reflexes elicited during normal gait are important for the regulation of locomotion. The cortex is thought to be involved in the control of reflexes during gait, but it is unclear whether it plays a role in the modulation of these reflexes during the step cycle. During gait, weak electrical stimulation of the sural nerve elicits reflexes in various leg muscles. Are these reflexes different when subjects themselves trigger the stimuli instead of being randomly released by the computer? Cutaneous reflexes were elicited by sural nerve stimulation in 16 phases of the gait cycle in healthy subjects. The stimuli were triggered either by computer or by the subjects themselves. In 6 out of 7 subjects it was observed that the facilitatory responses in leg muscles were smaller and the suppressive responses were more suppressive following self-generated stimuli. In some muscles such as tibialis anterior (TA) both effects were seen (reduced facilitation at end stance and exaggerated suppression at end swing). In all subjects the modulation of anticipatory influences was muscle specific. In the main group of six subjects, the mean reduction in reflex responses was strongest in the TA (max. 30.7%; mean over 16 phases was 12.5%) and weakest in peroneus longus (PL, max. 10.1%; mean over 16 phases was 2.6%). The observation that facilitation is reduced and suppression enhanced in several muscles is taken as evidence that anticipation of self-induced reflex responses reduces the excitatory drive to motoneurones, for example through presynaptic inhibition of facilitatory reflex pathways.

(Received 25 July 2005; accepted after revision 27 October 2005; first published online 3 November 2005)
Corresponding author J. Duysens: Department of Rehabilitation Medicine, Radboud University Nijmegen Medical Center, PO Box 9101, 6500 HB Nijmegen, The Netherlands. Email: j.duysens{at}reval.umcn.nl

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