Theoretical Study of Underlying Mechanism of Tremor with Reference to Its External Control

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The purpose of this study is to provide the means of analyzing tremor quantitatively with reference to its external control. Although tremor is expected to provide much neurological information, its underlying mechanism has not been clarified from the control-theoretical point of view so far. Previously, we proposed the two-reflex-loop model incorporating the spinal and supraspinal reflexes. In this study, attempts are made to validate the model experimentally and to develop the methodology of estimating the effect of external tremor control based on the model.Forced oscillation experiments are performed to validate the model. The wrist is fixed to a vibrator and hand acceleration and demodulated EMG are measured and analyzed by the FFT method. A systematic change in the phase angle between acceleration and demodulated EMG signals is observed. Results of simulation based on the model agree with the experimental results.In designing external tremor control by mechanical loading or external feedback, information is required of the tendency of oscillation. For the complex variable s=alpha+jomega in Laplace-transformed equations, the real part alpha can become positive or negative, corresponding to self-induced or damped oscillation, respectively. Hence alpha is considered to represent the tendency of oscillation. The effectiveness of this method is demonstrated by calculating the variables as functions of the two reflex loop gains.