Motor control in humans with large-fiber sensory neuropathy

Upper limb motor control was evaluated in a series of patients with a large-fiber sensory neuropathy associated with impaired position, vibration and cutaneous sensation and absence of deep tendon reflexes. Muscular strength was normal or only minimally affected. In studies of wrist movement it was found that both postural maintenance and accuracy of wrist displacement were heavily dependent on visual guidance. Without vision the limb would drift in almost random directions, and during intended movements both the trajectory and movement end-point were abnormal. The defects in posture and voluntary movement control were reflected in the inability of patients to maintain consistent levels or emit consistent patterns of muscle activity. It is concluded that whereas central motor commands are sufficient to initiate movements proprioceptive afferent inputs are important for accurate postural maintenance and the fine control of movement.