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Title: Spatial neglect and extinction : modulations by task, stimulus and prism therapy
Author: Sarri, Margarita
ISNI:       0000 0001 3553 3497
Awarding Body: University of London
Current Institution: University College London (University of London)
Date of Award: 2007
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Spatial neglect is a multi-component neurological syndrome, with the deficits including losses in awareness, attention and exploration towards the contralesional side of space, most commonly after right-hemisphere stroke. Neglect does not invariably affect just a fixed portion of space, but instead can be modulated by stimulation and task demands, including attentional factors. This thesis examines how aspects of neglect may be modulated by top-down task manipulations or bottom-up stimulus factors or by interventions, such as prism adaptation, that may have potential therapeutic benefit. The experiments show that varying top-down task-demands can substantially modulate neglect as revealed on cancellation measures similar to those commonly used in diagnosis. Specifically I show here that awareness for items towards the left space in cancellation tasks can be significantly modulated by just changing the task goal, and thus by directing the patients top-down attention to different aspects of the same stimulus displays. Prism interventions are found to improve awareness in neglect patients for certain tasks and stimulus types, but not others. Moreover, prism after-effects in neglect patients are found to be much larger when measured by subjective straight-ahead rather than open-loop pointing indices, which may be of importance for future studies of therapeutic impact from prism adapatation. Exploratory anatomical analyses indicate that this impact may also depend on the brain areas lesioned. Finally, using the phenomenon of extinction (a related sign to neglect) as a paradigm case of cross-modal modulation of awareness, the neural correlates of awareness or of unconscious processing were investigated by means of fMRI, in a patient with cross-modal extinction of left touch by right vision that affected perceptual sensitivity itself. This revealed that extinction and awareness do not correlate solely with activation within particular brain regions, but also relate to functional coupling between brain regions. These studies demonstrate various aspects of awareness that can be compromised following brain injury in neglect patients, and some of the factors that can modulate their awareness.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available