Research in the neural control of movement is only beginning to address the issue that bear on the control of multijoint movements. These issues arise, for the most part, from considerations of dynamics: the rotation about a joint does not depend exclusively on the muscular and external torques acting about that joint, but also depends upon the rotations about other joints. These interactions are due to inertial properties. It is important to study the strategies employed by the healthy nervous system for coping with the complexity of the dynamics of multijoint movement, for two reasons. First, the most apparent consequences of pathology in the neural motor-control system are disruptions in multijoint performance. Second, an understanding of normal multijoint control can be of immediate practical use in designing the strategies for artificial control of muscles by functional electrical stimulation in patients. The first specific aim of the present application addresses the rules whereby muscular torques chosen to initiate the movement. It is proposed that the nervous system may employ simple rules for this purpose, as an alternative to solving the complicated dynamics problem. Such simple rules, however, would not always result in the hand being launched in the target direction.
The second aim i s to test the hypothesis that reflex effects within and across joints are so organized that the direction of motion is corrected automatically. If true, this would provide a new perspective for understanding the role of reflexes in voluntary movements, a role which is currently controversial, perhaps because it has not been studied in the context of multijoint movements. These hypotheses will be tested by impeding or perturbing the movement by mechanical means, for a variety of arm configurations and target directions.
The third aim of the proposal represents an attempt at investigation of the process of braking of multijoint movements, an issue that has not been addressed before.

National Institute of Health (NIH)
National Institute of Neurological Disorders and Stroke (NINDS)
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Orthopedics and Musculoskeletal Study Section (ORTH)
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University of Arizona
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Pfann, Kerstin D; Corcos, Daniel M; Moore, Charity G et al. (2002) Circle-drawing movements at different speeds: role of inertial anisotropy. J Neurophysiol 88:2399-407
Koshland, G F; Hasan, Z (2000) Electromyographic responses to a mechanical perturbation applied during impending arm movements in different directions: one-joint and two-joint conditions. Exp Brain Res 132:485-99
Gram, M C; Hasan, Z (1999) The spinal curve in standing and sitting postures in children with idiopathic scoliosis. Spine (Phila Pa 1976) 24:169-77
Tyler, A E; Hasan, Z (1995) Qualitative discrepancies between trunk muscle activity and dynamic postural requirements at the initiation of reaching movements performed while sitting. Exp Brain Res 107:87-95
Koshland, G F; Hasan, Z (1994) Selection of muscles for initiation of planar, three-joint arm movements with different final orientations of the hand. Exp Brain Res 98:157-62
Karst, G M; Hasan, Z (1991) Timing and magnitude of electromyographic activity for two-joint arm movements in different directions. J Neurophysiol 66:1594-604
Karst, G M; Hasan, Z (1991) Initiation rules for planar, two-joint arm movements: agonist selection for movements throughout the work space. J Neurophysiol 66:1579-93
Hasan, Z; Karst, G M (1989) Muscle activity for initiation of planar, two-joint arm movements in different directions. Exp Brain Res 76:651-5
Hasan, Z; Stuart, D G (1988) Animal solutions to problems of movement control: the role of proprioceptors. Annu Rev Neurosci 11:199-223
Karst, G M; Hasan, Z (1987) Antagonist muscle activity during human forearm movements under varying kinematic and loading conditions. Exp Brain Res 67:391-401

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