Proprioception in the Upper Limb of Non-Disabled and Stroke-Impaired Populations
Stroke, the restriction of oxygen to a particular brain region, is a leading cause of adult disability. As many as 5.5 million Americans are living with motor deficits that were caused by a stroke. Up to ninety percent of these survivors experience some level of sensory dysfunction and approximately half face a specific deficit in proprioception, defined as the sense of one's body in space without the use of vision. In general, sensory loss—especially proprioceptive deficit slows sensensorimotor recovery. However, proprioceptive acuity is difficult to measure, and proprioceptive deficits in stroke impaired populations have not been thoroughly characterized.
We developed an assessment of proprioceptive position sense that brings together existing approaches from the literature in an attempt to isolate and characterize individual contributions to the overall proprioceptive percept. To facilitate our studies, we developed the chARM robot, a low-cost, open-source platform for studying sensorimotor control in the upper limb. We used our assessment approach and chARM to measure proprioceptive acuity in samples from the non-disabled (healthy) and chronically stroke-impaired populations. In the non-disabled sample, trends in proprioceptive acuity confirm major findings from the literature, as well as revealing a synergistic relationship between active and task-space assessments, which provides new insight into functioning of the brain's system for state estimation. In the stroke-impaired sample, we demonstrated a correlation between deficits in position sense and movement following stroke, refuting claims that the two are independent. Despite this correlation, we found only a weak relationship between scores on our robotic assessments of proprioception and movement and scores on the Fugl-Meyer Assessment, a commonly used clinical test of sensorimotor ability.
Our results deepen understanding of proprioception in general and begin to establish a relationship between proprioceptive and motor impairments after stroke. These findings could inform the design of post-stroke therapy, ultimately accelerating recovery during the window of high neural plasticity that immediately follows stroke, as well as increasing the efficacy of treatments that extend past this window.