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This Article Full Text Full Text (PDF) All Versions of this Article: 585/3/833    most recent jphysiol.2007.139089v1 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 Sturnieks, D. L. Articles by Fitzpatrick, R. C. Search for Related Content PubMed PubMed Citation Articles by Sturnieks, D. L. Articles by Fitzpatrick, R. C. Related Collections Neuroscience

¹ Prince of Wales Medical Research Institute and University of New South Wales, Sydney, NSW 2031, Australia

To detect joint movement, the brain relies on sensory signals from muscle spindles that sense the lengthening and shortening of the muscles. For single-joint muscles, the unique relationship between joint angle and muscle length makes this relatively straightforward. However, many muscles cross more than one joint, making their spindle signals potentially ambiguous, particularly when these joints move in opposite directions. We show here that simultaneous movement at adjacent joints sharing biarticular muscles affects the threshold for detecting movements at either joint whereas it has no effect for non-adjacent joints. The angular displacements required for 70% correct detection were determined in 12 subjects for movements imposed on the shoulder, elbow and wrist at angular velocities of 0.25–2 deg s^–1. When moved in isolation, detection thresholds at each joint were similar to those reported previously. When movements were imposed on the shoulder and wrist simultaneously, there were no changes in the thresholds for detecting movement at either joint. In contrast, when movements in opposite directions at velocities greater than 0.5 deg s^–1 were imposed on the elbow and wrist simultaneously, thresholds increased. At 2 deg s^–1, the displacement threshold was approximately doubled. Thresholds decreased when these adjacent joints moved in the same direction. When these joints moved in opposite directions, subjects more frequently perceived incorrect movements in the opposite direction to the actual. We conclude that the brain uses potentially ambiguous signals from biarticular muscles for kinaesthesia and that this limits acuity for detecting joint movement when adjacent joints are moved simultaneously.

(Received 19 June 2007; accepted after revision 16 October 2007; first published online 18 October 2007)
Corresponding author R. Fitzpatrick: Prince of Wales Medical Research Institute, Easy Street, Randwick, NSW 2031, Australia. Email: r.fitzpatrick{at}unsw.edu.au