LOSS OF PROPRIOCEPTION PRODUCES DEFICITS IN INTERJOINT COORDINATION

1. We analyzed the performance of a simple pantomimed gesture in 2 pat ients with large-fiber sensory neuropathy and 11 control subjects to d etermine how proprioceptive deafferentation disrupts unconstrained mul tijoint movements. Both patients had near-total loss of joint position , vibration, and discriminative touch sensation in the upper extremiti es. Muscle strength remained intact. 2. Subjects performed a gesture s imilar to slicing a loaf of bread. In this gesture, the hand first mov es outward from the body, reverses direction sharply, and then moves b ack toward the body. Accurate performance requires precise coordinatio n between the shoulder and elbow joints during movement reversals. Mov ements were performed under two conditions: with eyes open and with ey es closed. Three dimensional shoulder, elbow, wrist, and hand trajecto ries were recorded on a WATSMART system. 3. When control subjects perf ormed the gesture with their eyes closed, their wrist trajectories wer e relatively straight and individual cycles of motion were planar. Mov ements reversed direction sharply, such that outward and inward portio ns of the wrist path were closely aligned. Corresponding to this spati al profile, the reversals in movement direction at the shoulder joint, from flexion to extension, and at the elbow joint, from extension to flexion, were synchronous. 4. In contrast, when deafferented patients performed the gesture with their eyes closed, their wrist trajectories were highly curved and individual cycles were severely nonplanar. The wrist paths showed a characteristic anomaly during the reversal in mo vement direction, when elbow joint movement became transiently locked. Correspondingly, the movement reversals at the shoulder and elbow joi nts were severely temporally decoupled. 5. When patients were able to view their limbs during performance of this gesture there was signific ant improvement in the linearity and planarity of movements. However, the patients remained unable to synchronize the movements at the shoul der and elbow joints to produce spatially precise wrist paths. 6. We c onclude that loss of proprioception disrupts interjoint coordination a nd discuss the hypothesis that this interjoint coordination deficit re sults from a failure to control the interaction forces that arise betw een limb segments during multijoint movements.