Proprioceptive feedback control during human upper arm reaching movements

Human voluntary movements are controlled by a combination of feed-forward control and sensory feedback. Sensory feedback from muscle spindles provides velocity and position information of the ongoing movement. Previous studies have shown that proprioceptive feedback control is suppressed in the beginning of point-to-point movement, and is facilitated at the time of peak muscle torque. This raises a question that whether the suppression is determined by the movement initiation or by the acceleration phase of the movement. This question was investigated in the first study of this dissertation. Movements that involve multiple segments in a sequence were introduced since this type of movements involved multiple acceleration phases but were initiated only once. It was hypothesized and confirmed in the first study that the proprioceptive feedback control is suppressed and facilitated in the acceleration phase of both segment 1 and 2 within a movement. When the suppression is finished and proprioceptive feedback control is facilitated again, it is unknown how velocity information and position information are used to control the movement. The second study investigated how velocity feedback and position feedback are used to control upper limb reaching movements to a target. It was hypothesized and confirmed that the control of point-to-point movement includes a suppression of proprioceptive feedback followed by an interval of velocity feedback control, and then an interval of position feedback control. I experimentally tested both hypotheses by perturbing the movement using a servo-controlled manipulandum and a haptic robot. The responses in muscle surface electromyograms (EMGs) to the perturbation were analyzed. The rationale for this dissertation is that a better understanding of proprioceptive feedback will contribute to the knowledge of how accurate movements are performed. As such, it allows movement disorders to be explained as malfunctions in proprioceptive feedback control, therefore the current study is essential for innovative treatment and assessment of movement disorders.