Proceedings of The Physiological Society

Physiology 2012 (Edinburgh) (2012) Proc Physiol Soc 27, PC321

Poster Communications

The contribution of motor commands to position sense differs between wrist and elbow

L. D. Walsh1,2, U. Proske3, T. J. Allen3, S. C. Gandevia1,2

1. Neuroscience Research Australia, Sydney, New South Wales, Australia. 2. University of New Wales, Sydney, New South Wales, Australia. 3. Monash University, Melbourne, Victoria, Australia.

Proprioception is critical to movement control and it relies on information from multiple sources, including receptors in muscles, joints and skin. Recently it was shown that motor commands contribute to perceived position and movement at the wrist (e.g. Walsh et al., 2010). In contrast, at the elbow when the arm was loaded, no evidence emerged for a contribution from motor commands to position sense (e.g. Ansems et al., 2006). However, these two sets of experiments were performed at different joints using different methods to indicate joint position. The present study aimed to resolve the discrepancy by using both methods at both joints. Two experiments, each with 20 human subjects, were performed one at the wrist, the other at the elbow, each with two sessions. In the ‘single wrist' session subjects were seated at a table with their right arm strapped to the table and the hand in a device that restricted movement to the wrist joint. A 50% of maximum voluntary conditioning contraction of wrist flexor or extensor muscles controlled for contraction history. After relaxation, the wrist was moved to a test angle. Position was indicated with a pointer when the hand was relaxed or when the conditioned wrist muscles were contracting isometrically at 30% of maximum. In the ‘double wrist' session both arms were strapped into manipulanda, both arms performed the conditioning contraction and instead of using a pointer, the subject indicated the perceived position of the right wrist by matching its position with the left wrist. In a further 20 subjects a similar experiment was performed on the elbow joint using the same experimental design. In the single wrist session there was an effect of muscle contraction. This effect significantly (ANOVA, p < 0.001) changed subjects' perception of limb position by 7 ° [3, 12] (mean [95% confidence interval]) during a flexion contraction and 9 ° [4, 14] during an extension contraction. During the bilateral matching task in the ‘double wrist' session, contractions also had a significant (ANOVA, p < 0.01) effect, changing perceived limb position by 13 ° [9, 16] during flexion and by 5 ° [2, 8] during extension. Contraction of elbow flexors or elbow extensors did not significantly alter the perceived angle of the elbow. The results of the present study are consistent with the previous studies on the wrist and the elbow, cited above. Thus while an effect of muscle contraction on perceived joint position at the wrist has been confirmed, a similar effect is not detectable at the elbow joint. Furthermore, the method of indicating joint angle (pointing or matching) also seems to influence the size of the effect of muscle contraction. The findings confirm that centrally-generated motor command signals can contribute to joint position sense, but the importance of the contribution may depend on the joint.

Where applicable, experiments conform with Society ethical requirements