Date of Award
Master of Science (MS)
Scott A. Beardsley
Robert A. Scheidt
Sensorimotor error feedback plays an integral role in movement; it adapts the sensorimotor control system to rapid changes in environmental loads and allows smooth limb coordination. Studies have shown the cerebellum, parietal, and premotor cortices to be involved in error processing, but the specific neural function of those areas remain relatively unknown. The objective of this study was to characterize the neural sources that underlie the computation of visual and proprioceptive error during goal-directed movement. We tested the hypothesis that the cortical networks meditating the two sensory error systems are distinct.
Subjects (n=7) used a cursor to track a moving target presented on a computer display. Cursor position on the screen was yoked to a 1-D wrist manipulandum that recorded wrist position, velocity, and torque and applied controlled torques to the wrist. External displacement errors were applied as either force perturbations to the wrist (Proprioceptive condition) or visual displacements to cursor position (Visual condition). Five levels of displacement were applied to identify neural responses that co-varied with the magnitude of displacement. EEG was collected from 64 electrodes. Distributed cortical source modeling (Brainstorm v.3) identified cortical sources that contributed to the averaged EEG activity across error levels.
In force perturbation trials, current source density across subjects showed early somatosensory, premotor, motor, and frontal activity ranging from 43±5 ms to 48±6 ms, followed by parietal activity at 70±8 ms. In visual perturbation trials, parietal activation at 113±8 ms was followed by sensory, motor, and premotor activation (123±42 ms to 131±22 ms). Spatial analyses suggest error representations for proprioception and vision may be computed in spatially distinct areas of frontal and parietal cortices.
The temporal sequence of error-related activity suggests that sensorimotor error may not initially be computed in parietal regions before being processed in motor areas. The early premotor/motor activation in the Proprioceptive condition suggests that a course estimate of error is first computed in those areas before a more accurate representation of error is generated in the parietal regions. This may occur to initiate a course correction faster in the direction of the error while gathering more information about the error.