| Summary: | The current studies were conducted in search of a possible psychophysiological vulnerability marker for schizophrenia. A vulnerability marker for a specific illness needs to fulfil four main criteria; first, the marker needs to be under genetic control, second, it needs to be present in most individuals affected with a certain illness, third, it must not be dependent on the illness state of the patient and fourth, the trait must be associated with the transmission of the illness. The present thesis tested the first two criteria on three psychophysiological behaviours: (i) the P300 event-related potential, (ii) the dynamic power changes in the lower frequency ranges (delta, theta and alpha) of the electroencephalogram and (iii) visual scan paths. The first study investigated the genetic influence on the three measures by testing a sample of identical and non-identical twins. There was evidence that the P300 amplitude and the spatial distribution of visual fixations were the only two behaviours which were likely to be under genetic control. The same tests were administered to a sample of patients with schizophrenia, a sample of healthy participants and patients with bipolar disorder. Patients with schizophrenia exhibited decreased P300 amplitudes, decreased delta power, globally restricted scanning of images of varying semantic content and different visual fixation distributions compared to healthy controls. The schizophrenic and bipolar patients performed similarly on most tests and could be clearly differentiated on the basis of their visual fixation distributions. Given the results of the twin and patient studies, visual fixation distributions were the only possible trait marker specific to schizophrenia. It remains to be determined whether visual scan path variables change with the current state of the illness (acute compared to chronic) and whether these abnormal scanning patterns can be observed in first order relatives of affected individuals.
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