Interregional Connectivity in People with Schizophrenia: A Study Using Visual Evoked Potentials

Abstract

A parsimonious and complete understanding of schizophrenia continues to be elusive. There are many apparent contributing factors to the development of this disease. These include genetics, environment and developmental factors. Of particular interest to the current thesis are the reported changes in cerebral white matter laterality in people with schizophrenia. There is evidence that within the normal population transfer of information between the two cerebral hemispheres is faster from the right hemisphere to the left hemisphere than the transfer of information from the left to the right hemisphere. It has been proposed that this is a function of a greater ratio of fast conducting axons in the right hemisphere than in the left hemisphere. It has been observed that people with schizophrenia do not display this asymmetry of interhemispheric transfer time (IHTT). Instead, people with schizophrenia display no difference in information transfer time from the right to the left hemisphere and the left to the right hemisphere. It has been postulated that this is due to a reduction in fast conducting axons in the right hemisphere in people with schizophrenia. This thesis aimed to further investigate alterations in cerebral laterality of axonal type in males with schizophrenia. This experiment used a 128-channel electroencephalogram to record the averaged visual evoked potentials (AEPs), specifically the P100 and N160, generated using the Poffenburger paradigm in people with schizophrenia and control participants. Low Resolution Electromagnetic Tomography (LORETA) was used to estimate the sources of the bilateral AEP components and then to reconstruct the current density dynamics underlying these components. Both the raw AEPs and the source estimated latency data were analysed to compare IHTT and intrahemispheric, as well as absolute latencies within and between the groups. It was confirmed that IHTT in the normal population is faster from the right to the left hemisphere than the inverse and that people with schizophrenia have an altered IHTT. Furthermore, an interesting pattern of intrahemispheric and P100 and N160 absolute latencies was observed within both groups, and between groups. The findings from this thesis do indicate that people with schizophrenia have altered timing in visual information processing when compared with the normal population. This is hypothesised to be due to alterations in the distribution of myelinated white matter in the schizophrenia population, which is likely to affect cerebral communication and/or integration of information.