Impact of proprioceptive deficit on control of joint torques during force matching task in hemispheric stroke...

Proprioceptive loss is related to inaccurate initial reaching movement direction in chronic hemispheric stroke survivors, it potentially also impacts the predictive (feedforward) control of joint torques based on the target and current body joint positions, although this remains to be clarified. Accordingly, we sought to determine whether proprioceptive loss after stroke impairs predictive joint torque control when no visual feedback is provided.

While blindfolded, 12 chronic hemispheric stroke survivors performed a force direction matching task. Each participant's hand was passively moved by a haptic robot to multiple locations on a plane, where they were asked to exert forces in four cardinal directions. The severity of proprioceptive loss was assessed via the finger-to-nose, passive movement detection, and position reproduction tests.

We found that the participants with severe proprioceptive deficits on the aforementioned standard tests showed a significantly larger directional error in the generated forces than participants with less impaired or intact proprioception. Specifically, the patients with severely impaired proprioception generated forces in only two directions, corresponding to horizontal shoulder flexion and extension, rather than the four distinct cardinal directions. No significant correlation was found between other parameters (the tactile deficit and the maximum voluntary pushing force) and the directional error in the force direction matching test.

These results imply that the quality of proprioception significantly affects the accuracy of predictive control when generating joint torques, potentially due to inaccurate perception of the spatial representation of body joints.