Quantitative Probes to Explore Neural Mechanisms Driving Losses of Independent Joint and Limb Control Following an Early Unilateral Brain Injury


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A one-time, unilateral injury to the developing brain can interrupt the typical process of development and result in motor impairments that evolve over the course of the whole life-span. The timing of injury relative to neural development has implications for the continued refinement of the nervous system and the descending motor pathways available for control of extremities. Two categories of impairments seen in individuals with an early unilateral brain injury are losses of independent joint control and limb control. The presence or absence of these impairments after an early unilateral brain injury provides insight into the neural mechanisms employed for movement control. The goal of this dissertation is to use peripheral quantitative measures of movement and muscle co-activation patterns to explore the possible neural mechanisms resulting in movement impairments in pediatric hemiplegia. A haptic robotic device able to modulate shoulder abduction effort was used to quantify independent control of the shoulder and elbow joints during a ballistic reaching task. Between limb muscle co-activation patterns recorded during maximal isometric and submaximal dynamic tasks were used to evaluate independent limb control. Motion-tracking and pressure recordings were integrated with the haptic robot to measure independent finger control during a finger tapping task. Performance on all tasks was compared between participants with pediatric hemiplegia and age-matched peers without neurological impairments. Individuals with pediatric hemiplegia onset prior to six months of age performed similarly to peers without hemiplegia in their reaching distance but moved more slowly. Interestingly, participants who had their stroke before birth moved more slowly in both arms while participants who had their stroke at full term or within the first six months of life moved more slowly only in the affected arm. In both isometric and dynamic tasks, individuals with pediatric hemiplegia show greater muscle co-activation patterns between arms when compared to peers. Furthermore, muscle co-activation in the contralateral arm is more pronounced when activating the non-paretic arm, indicating a clear directionality of the mirrored activation. High resolution assessment of finger individuation with motion-tracking demonstrated ability to capture the finger with greatest impairment offering more detail of deficits than global clinical assessments of independent joint control. These results provide evidence that those with early-onset pediatric hemiplegia retain independent control of the shoulder and elbow but experience diminished independent limb control throughout the upper extremity. The presented approach to characterizing finger individuation provides a high-resolution tool to measure and monitor independent joint control of the hand which is the most impaired after early brain injury. This work overall motivates the consideration of timing of injury when selecting interventions to optimize use of remaining descending motor pathways.

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