Development of a quantitative evaluation system for motor control using wrist movements--an analysis of movement disorders in patients with cerebellar diseases

In this study, we developed a new system for quantitative evaluation of the wrist movement. We designed this system to analyze the causal relationship between movement disorders and abnormal muscle activities. In addition, this system was also designed to be non-invasive and used handily at the bedside. We tested this system for analysis of movement disorders in the cerebellar patients. As an experimental task, we asked subjects to perform step-tracking wrist movements with a manipulandum, and simultaneously recorded wrist joint movements and muscle activities of four wrist prime movers with surface electrodes. The participants included eight patients with cerebellar diseases and eight normal controls. First, we made quantitative analysis of movement kinematics in the cerebellar patients in terms of accuracy and directional deviation of wrist movements. Then we examined how well the wrist movement could be explained with the activities of the four prime movers. Specifically, we compared the wrist joint torque calculated from the movement of the wrist (kinematic torque) and the wrist joint torque estimated from the muscle activities (muscle torque). Then we evaluated match between the two. Our surprising observation was that there were very high correlations between the kinematic torque and the muscle torque for both normal controls and cerebellar patients. Correlation coefficients R for normal controls were 0.85 +/- 0.06 for X-axis component and 0.78 +/- 0.09 for Y-axis component. On the other hand, correlation coefficients R for cerebellar patients were 0.78 +/- 0.11 for X-axis component and 0.78 +/- 0.1 for Y-axis component. These results strongly suggested that there were enough information in the activities of the four muscles to explain the position, speed and acceleration of the wrist joint. In other words, with our system, it is possible to identify causal abnormality of muscle activities for movement disorders. Therefore, it is possible with our system to analyze movement disorders at a motor command level.