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Directional tuning of human forearm muscle afferents during voluntary wrist movements.

Journal article
Authors K E Jones
Johan Wessberg
Åke Vallbo
Published in The Journal of physiology
Volume 536
Issue Pt 2
Pages 635-47
ISSN 0022-3751
Publication year 2001
Published at Institute of Physiology and Pharmacology, Dept of Physiology
Pages 635-47
Language en
Keywords Adult, Electromyography, Female, Forearm, innervation, physiology, Humans, Male, Movement, physiology, Muscle Spindles, physiology, Muscle, Skeletal, innervation, physiology, Neurons, Afferent, physiology, Tendons, physiology, Volition, physiology, Wrist Joint, physiology
Subject categories Neurophysiology


1. Single unit activity was recorded with the microneurography technique from sixteen spindle afferents and one Golgi tendon organ afferent originating from the forearm extensor muscles. Impulse rates were studied while subjects performed unobstructed aiming movements at the wrist in eight different directions 45 deg apart. In addition, similar imposed movements were performed while the subject was instructed to remain relaxed. Movement amplitudes were about 5 deg and the speed 10-30 deg x s(-1). Joint movements were translated to movements of a cursor on a monitor to provide visual feedback. 2. Individual spindle afferents modulated their activity over a number of targets, i.e. were broadly tuned, during these aiming movements. The preferred direction for a spindle afferent was the same during both passive and active movements, indicating that the fusimotor effects associated with active contractions had little or no effect on the direction of tuning. 3. The direction of tuning of individual spindle afferents could be predicted from the biomechanically inferred length changes of the parent muscle. Thus spindle afferents responded as stretch receptors, i.e. impulse rates increased with lengthening and decreased with shortening, in active as well as passive movements. 4. Spindles from muscles, which continuously counteracted gravity exhibited a stretch response and directional tuning during the phase of movement alone whereas their position sensitivity was poor. In contrast, spindle afferents from the muscles that had no or minimal antigravity role were directionally tuned during both the dynamic and the static phase of the aiming task and their position sensitivity was substantially higher. 5. In spite of the limited data base from three extensor muscles it could be demonstrated that wrist joint position was remarkably well encoded in the ensemble muscle spindle data. In some cases the ensemble muscle spindle data encoded the instantaneous trajectory of movement as well.

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