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Title: Tests of corpus callosum and hemisphere function and their relevance to schizophrenic disorders
Author: David, Anthony Sion
Awarding Body: University of Glasgow
Current Institution: University of Glasgow
Date of Award: 1992
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Study of the neuropsychological functioning of the cerebral hemispheres and the transfer of information between them, can be achieved by presenting visual stimuli for processing, to one or other (or both) visual field(s), using a tachistoscope. Research of this kind has been applied to the study of schizophrenic disorders but the results remain inconclusive because of methodological problems in the execution of such studies. In this thesis, three novel tests were devised in an attempt to build upon and clarify this work. The tests were designed to have useful properties such as feasibility in the testing of psychotic patients and the ability to elicit clear lateralised asymmetries in performance by normal subjects. A series of experiments were undertaken to examine the effect that psychiatric disorders had on the performance of these tests. The bulk of the subjects who participated in this research included 52 normal controls, drawn mainly from the nursing, technical and ancillary staff of the Maudsley Hospital. The patients comprised of 46 schizophrenics at various stages of their illness, most of whom were in-patients. A psychiatric control group was also included and this consisted of 22 patients with affective disorder, 10 of whom were bipolar. Again, the majority were in-patients. All the patients were assessed using standardised semi-structured interviews and questionnaires, and diagnoses were made according to agreed international criteria. Essentially, all of the patients did all of the tests. A sub-group of 30 schizophrenics had CT scans and of these, 21 had magnetic resonance imaging (MRI). The first test involved the processing of pictorial stimuli. The test had two components: one required the classification of the item depicted as being either living or non-living, which produced a left hemisphere (LH) advantage. The other, using the same stimuli, required a judgement of size in comparison with a standard referent using mental imagery; this produced a right hemisphere (RH) advantage provided the size comparison was sufficiently taxing. When the patients performed these tasks, they showed the expected RH advantage for the size comparison, although their reaction time was slowed, presumably due to non-specific effects of illness and medication. However, the schizophrenic group, while showing no abnormality of mental imagery in the RH, failed to demonstrate an LH advantage on the categorisation task and this was particularly so for those who had experienced visual hallucinations. This was interpreted as a deficit in visual semantic memory in the LH. The second test employed chimeric face drawings in which half of the face looked happy and the other looked sad. It was shown that normal right handers were biased in their judgements of whether the composite face looked happy or sad by the affective valence of the half-face to their left. The effect was highly significant, robust and reliable. This was not found in non-right handers. The perceptual bias evoked by the stimuli was interpreted as a function of the normal RH's role in directing spatial attention. The influence of affect, also thought to involve the RH, was examined by inducing different moods in a sub-group of normal subjects and found to be insignificant. When the same stimuli were presented tachistoscopically, to a different group of normal controls, the same perceptual bias was elicited. Patients with manic or depressive illness showed an increase and decrease in the strength of the bias, respectively. Schizophrenic patients showed a significantly reduced bias suggesting RH impairment in attentional processes. A proportion of the subjects also performed on a test of selective attention. The normal pattern of correlations between this, and bias and reaction time on the chimeric faces test, appeared to break down in the schizophrenics, suggesting widespread disruption of attentional systems. Distinct patterns of inter-correlations were observed for each of the subject groups. The third test was designed to determine the extent and nature of interhemispheric transfer of information, across the corpus callosum. A tachistoscopic version of the Stroop colour-word test was used in which the 2 elements were separated across the mid-line. A "control", intrahemispheric version was also administered. In normals subjects, interference and facilitation of colour naming by colour-words was reduced in the interhemispheric condition relative to the intrahemispheric condition. This situation was exaggerated in subjects with agenesis of the corpus callosum. When patients with schizophrenia were administered this test, they showed a unique pattern of results. As a group, the amount of Stroop interference and facilitation which occurred across the corpus callosum was greater than within the hemispheres. Otherwise, their performance was comparable to the controls. This did not appear to be related to clinical variables including, age, IQ, the severity of psychotic symptoms or a positive family history, although there was a trend for recovered patients to show the effect to a greater degree.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (M.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available