A central focus of experimental and theoretical studies of motor control is how the brain interacts with the external world to produce coordinated voluntary movement in the presence of unexpected changes in the environment. The two main mechanisms by which movement is produced are predictive feedforward control and sensory feedback control. The interplay of these two mechanisms in single-joint goal-oriented movements will be studied. The central hypothesis of this application is that the neural control of point-to-point movement made with fast or moderate speed consists of three stages, 1) feedforward control in the beginning of the movement, 2) velocity feedback control in the middle of the movement, and 3) position feedback control at the end of the movement. The duration of the feedforward stage 1 of control is determined only by the timing parameters of the movement task. The velocity and position control will be dissociated by imposing unexpected deviations in the movement kinematics and analyzing the electromyographic responses in muscles producing the movement.
Three specific aims are designed to test the central hypothesis by systematically varying the parameters of the imposed kinematics deviations and movement tasks. Simple point-to-point movements will be studied in the first two aims.
The first aim i s designed to test the initial suppression of feedback control.
The second aim i s designed to dissociate the velocity and position control when feedback is activated.
The third aim i s designed to investigate the temporal structure of control in movements with multiple sub- movements. The technical innovation of this proposal is that velocity and position deviations from the expected trajectory will be directly controlled by means of servo control of a torque motor. The neurophysiological innovation of this proposal is that the experiments will elucidate the temporal structure of feedback control during movement and dissociate the velocity and position components of feedback control. Movements are impaired in individuals with motor disorders such as spasticity, Parkinson's disease, and Huntington's disease. These motor disorders affect the mechanisms of sensory feedback. The proposed research will focus on the activity of feedback mechanisms based on proprioceptive input from muscle receptors during voluntary movement and will ultimately contribute to understanding the motor disorders in which these mechanisms are impaired. ? ? ? ?
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