Quantitative evaluation of movement disorders in neurological diseases based on EMG signals

In this paper, we propose a new method to make a quantitative evaluation for movement disorders. Based on the EMG signals, we analyzed the movement disorders for cerebellar patients at the motor command level. 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. In order to quantitatively evaluate the correspondence between the movement kinematics and the activities of the four muscles, we approximated the relationship between the wrist joint torque calculated from the kinematics and the four EMG signals using a dynamics model of wrist joint. Our surprising observation was that there was very high correlation between the wrist joint torque and the EMG signals. In fact, we identified causal abnormality of muscle activities for movement disorders of cerebellar patients, confirming effectiveness of our proposed method for analysis of movement disorders at the level of the motor command.