Year: 2012
Type: dissertation
Study design: Observational Study
Abstract: The formation of a visual percept in the human brain involves multiple processes, the \nextent of which may be related to each other within individuals but may show \nvariability between participants. The aim of this thesis was to investigate the \nrelationships between individual variability in various measures of visual processing. \nThe non-invasive neuroimaging methods of magnetic resonance imaging (MRI), \nmagnetic resonance spectroscopy (MRS), magnetoencephalography (MEG) and \nfunctional MRI (fMRI) were employed to measure brain structure, neurotransmitter \nconcentration, neuronal oscillations and haemodynamic activity, respectively. \nReductions in haemodynamic activity in non-stimulated areas of visual cortex \n(negative blood oxygen level-dependent responses) were shown to hold useful \ninformation about the stimulus, in addition to the responses in stimulated cortex. In \ngeneral, there were no strong relationships between increased or decreased functional \nresponses in visual cortex and measures of brain structure or of neurotransmitter \nconcentration. Age was the major determinant of individual variability in the \nfrequency of neuronal oscillations. These findings do not replicate results from \nprevious studies that have shown links between individual differences in these \nmeasures. This discrepancy was not due to poor repeatability of MRS measures, \nsince methods for optimisation of MRS were identified in this thesis. Simulations \nwere also conducted to determine the sample sizes required in correlational studies \ninvolving neuroimaging measures with associated measurement noise. The lack of \nreplication of relationships between neuroimaging measures of individual differences \nin visual processing is likely to be influenced by low statistical power, due to the \nsmall sample sizes and weak relationships tested. Such studies should therefore be \nconducted and interpreted cautiously, bearing in mind issues of power, demographic \nmediators of relationships and the likely strength of relationships inferred from the \nphysiological mechanisms linking the variables tested.
Author: Siân E. Robson
Language: English
Subfield: Cognitive Neuroscience
Field: Neuroscience
Domain: Life Sciences
Open Access status: green
OpenAlex ID: W1895404326