Somatosensory Perception During Motor Activation Post-Hemiparetic Stroke

Cai, Ninghe May

doi:https://doi.org/10.21985/n2-nrdr-w320

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Somatosensory Perception During Motor Activation Post-Hemiparetic Stroke

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Simple sensorimotor tasks, such as lifting a cup or balancing a tray, requires not only controlled motor output, but also the ability to accurately perceive sensory information. After a hemiparetic stroke, individuals often experience sensory deficits in addition to motor impairments. However, research on the extent of changes in sensory perception after stroke is limited, partly due to the lack of a repeatable and quantifiable approach to quantify sensory perceptual outcomes during motor tasks. To expand our understanding, this thesis work quantifies the impact of motor activation on somatosensory perception following hemiparetic. I first show that a novel torque-matching protocol in which participants match torques generated about a single joint while performing a multi-joint task is a viable approach to assess the perception of torque. This approach involves a single arm and allows for multi-joint activation. Using this approach, I address limitations of previously-used bilateral matching protocol by isolating the arm(s) at which the deficit occurs and quantifying perception during more complex movements. Using this protocol, through a series of experiments in adults without neurological impairments, I show that one’s perception of a self-generated torque at a single joint is influenced by the motor effort required for the entire task. This means during a complex multi-joint task, the perception of torques is not organized at the level of individual joints, but at a higher level related to the motor commands. After a hemiparetic stroke, the efferent drive may be altered due to the disruption to the corticobulbar tracts. Consequently, individuals post-hemiparetic stroke often exhibit a loss of independent joint control; self-generated torques are typically accompanied by a non-volitional activation. I show that non-volitionally generated torques in the paretic arm are not accurately perceived. This finding suggests that the presence of the abnormal flexion synergy post stroke could interfere with one’s perception of torques, which may in turn exacerbate the motor impairment. In this thesis, I also investigate the role of motor activation in tactile perception post hemiparetic stroke. The perception of tactile stimuli can be modulated during motor activation via sensory gating as demonstrated in individuals who are neurologically intact. I show the detection threshold in the paretic arm is greater than that in the non-paretic arm, indicating a diminished tactile perception. However, during motor activation, the detection threshold of a tactile stimulus increases in the paretic arm similarly to that in the non-paretic arm and controls. This finding supplements the current literature on the tactile perception after stroke, most of which were done when individuals were at rest. Taken together, this thesis work highlights changes in somatosensory perception during motor activation following stroke and the need to focus on sensorimotor integration when considering rehabilitation strategies.

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