Adaptation of arm movement control under repeated perturbations

To develop control strategies for a prosthetic arm or electrical stimulation of paralyzed muscles, we have designed a novel approach to investigate how the neural system utilizes available sensory information to learn and adapt to a perturbation for the intended arm reaching movement. A parallel approach of both human and animal experiments allows us to collect data from cortical neurons, muscles and arm movement kinematics to analyze coordinated changes in control strategy of various levels in the sensorimotor system. We simultaneously record neural activities in motor cortex, EMG responses in 7 arm muscles, and arm movement trajectories during a visually guided reaching task. Force perturbations (an impulse of 75-100 ms) are delivered through a string attached to the wrist of the moving arm. Preliminary results and data analysis demonstrate that human subjects develop an anticipatory strategy to improve performance of reaching tasks under repeated force perturbations applied to the wrist. The same experimental protocol has been modified to rhesus monkeys with implanted multi-channel cortical electrodes. Data collected from this experiment show that correlation of adaptation among individual and populations of cortical neurons, muscle coordination patterns, and kinematics can be established.