Determining the Brainstem’s Role in Loss of Independent Joint Control in Chronic StrokePublic Deposited
Following a stroke, precise, individuated control of single joints is often replaced by highly stereotyped patterns of multi-joint movement, due to a loss of independent joint control, which can negatively impact functional use of the paretic arm. Despite the debilitating nature of this impairment, the precise underlying neural mechanisms remain uncertain. Previous research has suggested that following stroke-induced damage to descending motor pathways in the lesioned hemisphere, contralesional corticobulbospinal pathways, such as the corticoreticulospinal pathway, become more heavily relied upon; however, these pathways have not been studied directly in human stroke individuals. Therefore, the goal of this work is first to determine whether structural and functional neuroanatomical correlates of the corticoreticulospinal tract are altered in chronic hemiparetic stroke when compared to healthy, age-matched controls and second, to determine whether structural and functional neural changes are directly related to loss of independent joint control in chronic stroke. This work combines multi-modal neuroimaging with rehabilitation robotics to determine whether brain structure and function in chronic stroke support the hypothesis of increased reliance on contralesional cortico-reticulospinal pathways contributing to loss of independent joint control. Three types of MR imaging are used to assess structure (white matter and gray matter) and function in both chronic stroke and healthy control individuals. In the lesioned hemisphere, stroke individuals display evidence of white matter damage and degeneration when compared with controls. However, in the contralesional hemisphere, stroke individuals display evidence of increased white matter microstructural integrity. This effect is particularly evident in those individuals with the greatest levels of motor impairment. Resting state functional connectivity is increased in stroke when compared to controls, and gray matter integrity in the contralesional motor cortex is also increased in the most severely impaired individuals. Finally, specific contralesional neural substrates correlate significantly with a quantitative robotic measurement of loss of independent joint control. This work demonstrates direct evidence for increased reliance on contralesional corticoreticulospinal pathways in chronic hemiparetic stroke, especially in the most severely impaired individuals. It emphasizes a need to better understand the neuroplastic changes that occur over time in the brain after stroke, particularly in the brainstem, in order to eventually be able to design more patient-specific and targeted therapeutic interventions.