The neurocognitive substrates of naming facilitation in aphasia: An fMRI investigation.

Shiree Heath (2012). The neurocognitive substrates of naming facilitation in aphasia: An fMRI investigation. PhD Thesis, School of Health and Rehabilitation Sciences, The University of Queensland.

       
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Author Shiree Heath
Thesis Title The neurocognitive substrates of naming facilitation in aphasia: An fMRI investigation.
School, Centre or Institute School of Health and Rehabilitation Sciences
Institution The University of Queensland
Publication date 2012
Thesis type PhD Thesis
Total pages 205
Total colour pages 6
Total black and white pages 199
Language eng
Subjects 170204 Linguistic Processes (incl. Speech Production and Comprehension)
110321 Rehabilitation and Therapy (excl. Physiotherapy)
170101 Biological Psychology (Neuropsychology, Psychopharmacology, Physiological Psychology)
Abstract/Summary Naming deficits are commonly experienced post-stroke and, given their high incidence and detrimental consequences, these impairments are frequently targeted in the treatment of aphasia. Evidence suggests that certain techniques can facilitate naming in aphasia, however, the neural mechanisms underpinning training-induced success remain unclear. This thesis aimed to advance our understanding of the mechanisms responsible for naming facilitation in the unimpaired brain and, importantly, to elucidate the neurocognitive substrates of naming facilitation in aphasia. Further, it aimed to determine whether such effects differ based on the type and timing of prior facilitation. The functional magnetic resonance imaging (fMRI) studies forming part of this thesis achieved these aims by utilizing two targeted language tasks that have been demonstrated to be effective facilitation techniques in individuals with aphasia. The level of processing required (either at the semantic or phonological level) in each language task was deliberately manipulated and allowed investigation of the potential locus of any positive effects upon subsequent naming performance. By manipulating the timing of prior facilitation using these tasks, either over the short-term (a period of minutes) or the long-term (a period of several days), the studies were also able to investigate the longevity of any facilitation effects. To our knowledge, no other neuroimaging studies have utilized this design to explore the underlying mechanisms involved in successful overt picture naming following facilitation, with targeted tasks over different timeframes, in individuals with aphasia and healthy controls. The thesis is comprised of four studies: semantic and phonological facilitation studies in both healthy individuals and in aphasia. The semantic studies investigated the behavioural and neurocognitive effects of naming facilitation using a semantic task in the absence of the phonological word form, and the time course of such effects. One experiment using this facilitation technique was conducted upon healthy controls and a second experiment, using exactly the same technique, was conducted upon individuals with aphasia. Although both subject groups benefited behaviourally from facilitation with a semantic task, different patterns of neural activation were evident. Modulation of activity was identified within regions associated with lexical-semantic processing, over the long-term for controls and over both the long- and the short-term for participants with aphasia. However, short-term facilitatory effects for control participants were found in regions linked to episodic memory and object recognition mechanisms. The phonological studies explored the effects of naming facilitation from a phonologically-based auditory repetition task administered in the presence of a picture. An experiment using this technique was conducted with healthy controls and a separate experiment with individuals with aphasia. Greater positive behavioural effects were shown in this phonological study than in the semantic study, for both controls and participants with aphasia. Additionally, the neuroimaging results suggested that the facilitatory effects arising from a phonological task were less selective, engaging regions associated with phonological and semantic processing in both controls and individuals with aphasia. For both subject groups these effects were evident over the long- and the short-term, with the short-term effects for control participants contributed to by modulation of activity in an area known to be involved in phonological processing. In summary, both techniques were effective in facilitating subsequent picture naming in controls and participants with aphasia to varying degrees. Taken together, the facilitation effects of a semantic verification task appeared to be somewhat selective in engaging regions associated with more efficient lexical-semantic processing during subsequent naming. On the other hand, an auditory repetition task was slightly more effective and less selective, engaging regions linked to both semantic and phonological processing, consistent with a strengthening of the connections between the two levels of processing. Although no distinct patterns emerged across individuals with aphasia regarding broader mechanisms of recovery, the results did provide evidence that right hemisphere mechanisms may be supportive of naming facilitation rather than maladaptive, and highlighted the involvement of regions not traditionally associated with language processing, particularly the cerebellum. Together, these experiments suggest that distinct neurocognitive mechanisms underlie the facilitation of naming by semantic and phonological tasks in both subject groups. An advance in our understanding of these mechanisms will inform the therapeutic facilitation of naming in the recovery of word production abilities following neurological injury. Therefore, these findings may aid the development of theoretically driven treatment selection methods and ultimately result in the provision of more targeted therapy for individuals with aphasia.
Keyword aphasia
fMRI
picture naming
facilitation
priming
phonology
auditory repetition
semantics
semantic verification
Additional Notes Colour: 65,79,101,120,137,157 Landscape: 80-82,95,96,138-140,152,153

 
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Created: Wed, 27 Jun 2012, 14:56:43 EST by Shiree Heath on behalf of Library - Information Access Service