Year

2004

Degree Name

Doctor of Philosophy

Department

Department of Psychology - Faculty of Health & Behavioural Sciences

Abstract

The P300 component of the auditory ERP elicited to target stimuli has been extensively investigated as a potential psychophysiological marker in schizophrenia. Theoretical and empirical evidence is presented, suggesting the earlier components (N100, P200) to both target and non-target stimuli may better capture information processing deficits currently proposed to be central to schizophrenia. The thesis comprises 4 studies. Study 1 demonstrated deficits to non-target (reduced N100 amplitude, earlier P200 latency), in addition to target stimuli (reduced and earlier N100 amplitude, increased P200 amplitude), in schizophrenia (n = 40) compared with matched normal controls. The schizophrenia group was also characterised by a lack of differentiation between ERPs elicited to target and non-target stimuli, in comparison to the normal control group. Study 2 confirmed the results of Study 1 in groups of chronic (chronic schizophrenia, n = 40) and first episode schizophrenia (FESz, n = 40), and additionally established that in normal controls non-target stimuli occurring immediately before the target (T-1) generated larger N1 amplitudes than the nontarget after (T+1), a pattern that failed to occur in Chronic schizophrenia and was minimal in FESz. N100 amplitude deficits to non-target stimuli were also correlated with clinical symptomatology, particularly with higher levels on the disorganisation factor. Most importantly, N100 and P200 responses to target and non-target (T+1 & 11 T-1) stimuli, were superior predictors in classifying both first episode and chronic schizophrenia patients than were the more commonly employed P300 measures. Study 3 examined the effect of certain sequence types on ERPs in FESz (n =14) and normal controls (n = 14), in order to ascertain whether P300 and other ERP deficits in schizophrenia could be attributed to impairments on specific sequence occurrences. Specifically, effects from the discontinuation of a long series of repetitions (DR-series) and alternations (DA-series) were examined. In general, patients with FESz demonstrated similar ERPs to controls to the series examined. Study 4 demonstrated that the early (N100 and P200) component deficits to target and non-target stimuli were specific for FESz (n = 20), when compared to both a clinical (ADHD, n = 20) and normal (n = 20) control group. Finally, a stepwise discriminant function analysis (Dfa), demonstrated that measures derived from the early components had better sensitivity and specificity values (vs. N2, P3) for diagnostic classification when compared with ADHD. This thesis provides compelling evidence that N100 and P200 components to target and non-target stimuli are impaired in both the early and chronic manifestations of schizophrenia, and argues that, on account of the superior sensitivity and specificity values associated with the early components, they may serve as potentially useful biological markers for the disorder.

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Unless otherwise indicated, the views expressed in this thesis are those of the author and do not necessarily represent the views of the University of Wollongong.