Assessing Impairments in the Use of Sensory Feedback for Motor Action Post-stroke

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Bourke, Teige
stroke , upper limb , robotics , assessment
Stroke is a leading cause of disability that can result in a variety of motor, sensory, and/or cognitive deficits. Importantly, use of sensory feedback to guide motor actions, a crucial component of voluntary motor control, may be compromised in these individuals. Assessment of these impairments is important to guide decisions about clinical rehabilitation. However, current clinical tools are often subjective and use coarse criteria-based scoring. We took a novel approach of using a robotic exoskeleton to provide objective and continuous measures of impairments post-stroke. Subjects with stroke and non-disabled controls were assessed on a series of robotic tasks. Impairments were defined as performance outside the range of 95% of non-disabled controls. In our first study, we assessed the use of limb afferent feedback to make a motor corrective response with a postural perturbation task. Up to 79% of subjects with stroke had impairments in the coordination, timing, and/or accuracy of their corrective responses. Interestingly, impairments were often bilateral. In our second study, we investigated whether impairments in the use of limb afferent feedback for action and perception are independent. Stroke-related impairments were independent in the perturbation and limb position matching tasks, both of which rely entirely on limb afferent feedback (Fisher, p=0.79). Performance was weakly correlated between the perturbation and visually-guided reaching task, both of which are motor tasks (rs=0.39, p=0.002). Thus, each task provides unique information of individual impairments post-stroke. In the final study, we designed an Object Hit and Avoid task where subjects were instructed to hit target objects falling from the top of the screen while avoiding distractor objects. Up to 78% of subjects with stroke were identified as impaired in task parameters and 50% had impaired hit selectivity. The specificity of objects hit was correlated with cognitive function (rs=-0.49, p=2x10-10). The results of this thesis highlight that many individual subjects with stroke have impairments in the use of sensory feedback to select and control motor actions. These tasks provide unique information on impairments associated with stroke. Future studies are necessary to identify how this information may guide patient-centered rehabilitation to ameliorate the effects of stroke.
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