Proprioceptive control of multijoint movement: unimanual circle drawing

The present experiments addressed whether proprioception is used by the cen tral nervous system (CNS) to control the spatial and temporal characteristi cs of unimanual circle drawing. Circle drawing is a multi-joint movement, i n which the muscles crossing the elbow and the shoulder are sequentially ac tivated. The spatial and temporal characteristics of circle drawing depend on the precise coordination of these sequential activation patterns, and pr oprioception is ideally suited to support this coordination. Blindfolded hu man subjects produced a counterclockwise circular drawing motion (diameter = 16 cm) with the dominant arm at a repetition rate of 1/s. In some trials, 60-70 Hz Vibration was applied to the tendons of the biceps brachii and/or the anterior deltoid. Spatial parameters measured from hand-movement data included the x- and y-axis diameters, circularity, and drift of the hand in the workspace. Vibration of either the biceps brachii or the anterior delt oid caused subjects to draw circles with decreased diameter, with changes i n circularity, and with a systematic drift of the hand. These distortions t o circle drawing by tendon vibration demonstrate that the CNS uses proprioc eptive information to accomplish the spatial characteristics of this motor task. Simultaneous vibration of both muscles produced a drift that exceeded the individual vibration effects, which suggests that the CNS combined pro prioceptive information related to elbow and shoulder rotation to control t he movement of the hand. The temporal characteristics of circle drawing wer e quantified from joint angle data. While vibration did not significantly i nfluence the relative phase between elbow and shoulder rotation, the variab ility of the phase relationship increased significantly, which suggests tha t proprioception contributes to phase stabilization. During circle drawing, elbow flexion-extension movements were produced with limited activation of the biceps. Nevertheless, biceps vibration distorted the circle metrics, s uggesting that a muscle's significance as a sensory transducer is independe nt of its activity level.