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This Article Full Text Full Text (PDF) All Versions of this Article: 97/6/4069    most recent 00909.2006v1 Alert me when this article is cited Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Similar articles in ISI Web of Science 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 Raptis, H. A. Articles by Feldman, A. G. Search for Related Content PubMed PubMed Citation Articles by Raptis, H. A. Articles by Feldman, A. G.

Vestibular System May Provide Equivalent Motor Actions Regardless of the Number of Body Segments Involved in the Task

¹Neurological Science Research Center, Department of Physiology, University of Montreal and Center for Multidisciplinary Research in Rehabilitation (CRIR), Rehabilitation Institute of Montreal, Montreal; ²Jewish Rehabilitation Hospital, CRIR, Laval, Quebec; and ³School of Rehabilitation Sciences, University of Ottawa, Ottawa, Ontario, Canada

Submitted 24 August 2006; accepted in final form 4 April 2007

The vestibulospinal system likely plays an essential role in motor equivalence—the ability to reach the desired motor goal despite intentional or imposed changes in the number of body segments involved in the task. To test this hypothesis, we compared the ability of healthy subjects and patients with unilateral vestibular lesions (surgical acoustic neuroma resection 0.6 to 6.7 yr before the study) to maintain either the same hand position or the same trajectory of within arm reach movements while flexing the trunk, in the absence of vision. In randomly selected trials, the trunk motion was prevented by an electromagnetic device. Healthy subjects were able to preserve the hand position or trajectory by modifying the elbow and shoulder joint rotations in a condition-dependent way, at a minimal latency of about 60 ms after the trunk movement onset. In contrast, six of seven patients showed deficits in the compensatory angular modifications at least in one of two tasks so that 30–100% of the trunk displacement was not compensated and thus influenced the hand position or trajectory. Results suggest that vestibular influences evoked by the head motion during trunk flexion play a major role in maintaining the consistency of arm motor actions in external space despite changes in the number of body segments involved. Our findings also suggest that despite long-term plasticity in the vestibular system and related neural structures, unilateral vestibular lesion may reduce the capacity of the nervous system to achieve motor equivalence.