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Title: Assessing sensorimotor plasticity with multimodal magnetic resonance imaging
Author: Kolasinski, James
ISNI:       0000 0004 5353 5594
Awarding Body: University of Oxford
Current Institution: University of Oxford
Date of Award: 2014
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The sensorimotor network receives a rich variety of somesthetic afferents and outputs considerable motor efferents, both of which drive experience-dependent plasticity in the system. It remains unclear to what extent subtle changes in somaesthesis and motor function extrinsic to the brain drive plasticity in the functional organisation and anatomy of the sensorimotor network. This thesis contains a series of multimodal MRI experiments to investigate how altered-use and disuse can induce plastic changes in the sensorimotor network of the human brain. In Chapter 3, a method of mapping digit somatotopy in primary somatosensory cortex at the single-subject level using 7.0 tesla fMRI was developed and applied for a study of healthy participants. Using a phase-encoding paradigm, digit representations were accurately mapped in under 10 minutes. These maps were reproducible over time and comparable to a standard block design. In Chapter 4, a further fMRI study assessed the potential for short-term reorganisation of digit representations in primary somatosensory cortex following a manipulation whereby the right index and right middle fingers were glued together for 24 hours. There was a marked shift in the cortical overlap of adjacent digits after the glued manipulation, not seen across an equivalent control period, providing strong evidence for short-term remapping of primary somatosensory cortex. In Chapter 5, a patient study investigated plasticity associated with chronic unilateral disuse of the upper limb. A cross-sectional comparison with control participants showed reduced grey matter density in the posterior right temporoparietal junction, and increased radial diffusivity in the white matter of the right superior longitudinal fasciculus, consistent with change in the right ventral attention network. A complementary longitudinal study in Chapter 6 investigated structural plasticity associated with rehabilitation of the disused limb. There were localised increases in grey matter density, notably in the right temporoparietal junction, further implicating a potential role for regions responsible for egocentric attention in regaining upper limb use. In Chapter 7, a further patient study investigated candidate predictive biomarkers at the sub-acute stage of stroke recovery, identifying CST-lesion cross-section and sensorimotor network strength as correlates of motor function, which warrant further study. The results of the studies presented in this thesis provide a novel insight into the nature and time frame of functional and structural plasticity associated with altered use and disuse. Further study of how subtle changes in our sensory and motor use shape the sensorimotor network is warranted, particularly in the context of disuse in non-neurological clinical populations.
Supervisor: Johansen-Berg, Heidi; Stagg, Charlotte J. Sponsor: Martin Wronker/Cephalosporin Scholarship ; Wellcome Trust
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: Neuroscience ; Plasticity ; Somatosensory cortex ; Motor Cortex