Mardell, Lydia Catherine; (2023) Cortical and spinal physiology in chronic stroke survivors with upper limb impairment. Doctoral thesis (Ph.D), UCL (University College London).

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Abstract

Upper limb impairment is common in stroke survivors and can result in decreased independence and quality of life. For many stroke survivors, upper limb impairment persists to the chronic stage, although some can still make considerable improvements with the appropriate rehabilitation. Phenotyping sensorimotor neurophysiology after stroke is a candidate for helping to determine the capacity for further recovery. Personalising rehabilitation requires a greater understanding of how stroke impacts the sensorimotor system and consequently influences upper limb function. In this thesis, I study neurophysiology at the cortex, brainstem and spinal cord, and examine how this relates to upper limb impairment after stroke. Cortical beta activity, which is underpinned by transient events called beta bursts, is altered after stroke, and related to upper limb recovery. During an isometric hand grip task, I found no significant differences in average beta activity between stroke survivors and healthy controls. Reduced burst duration in stroke survivors was the only significant change observed when studying individual beta bursts. Additionally, although the interhemispheric ratio of beta burst duration and amplitude were more bilateral after stroke, no modulation to beta burst-related interhemispheric connectivity was identified. Damage to the corticospinal tract contributes to upper limb impairment after stroke and the reticulospinal tract may compensate for this damage. By measuring the strength of these pathways in relation to each other and upper limb function in chronic stroke survivors, I found that corticospinal, not reticulospinal, strength predicts upper limb function, with no relationship seen between the two pathways. Stroke alters physiology at multiple levels of the central nervous system. Currently, it is not possible to image cortical and spinal neurophysiology concurrently. To address this, I developed a new imaging method, magentospinoencephalography (MSEG), that I use here to record cortical and spinal evoked fields during peripheral nerve stimulation in healthy adults. I detected early spinal evoked fields, concurrent with typical cortical responses. Future applications of this technique in stroke survivors will enable non-invasive imaging of the whole sensorimotor system.

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