Analysis of Semantic and Working Memory in Schizophrenia by Event-Related Potentials

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We have examined a pathophysiology of schizophrenia observed in the domains of cognitive functions such as perception, thinking (language), and memory by using a new experimental paradigm in visual event-related brain potential study, and found aberrant NA and N400 potentials in remitted patients, which reflect a pattern-recognition and a semantic processing, respectively. Our prospective follow-up study confirmed the NA abnormality to be a vulnerability marker of psychotic relapse characterized by florid hallucination and delusion. This study was designed to investigate a pathogenesis of N400 abnormality in schizophrenia and its clinical significance with a special reference to schizophrenic thought disturbance assessed by Thought Disorder Index (TDI) (Johnston and Holzman 1979).Parameters of N400 did not correlate to those of NA, and N400 abnormality was clearly observed in repetition priming rather than semantic processing of Japanese words. Repetition priming f N400 did not correlate to the total TDI scores. Then we divided into low TDI and high TDI patients according to TDI scores, and found a robust correlation between repetition priming and thought disturbance only in high TDI patients. These results suggest that aberrant N400 may be independent of NA abnormality, that aberrant N400 may not be due to a deficit in N400 generation mechanism (semantic processing) but a deficit in N400 regulation mechanism (memory processing), and that a part of schizophrenic thought disturbance may be caused by a deficit in working memory.Recent studies have reported that schizophrenic symptoms consist f three dimensions ; psychotic symptoms (hallucination and delusion), formal thought disorder, and deficit symptoms. In addition to such a clinical heterogeneity in schizophrenia, our data suggest a heterogeneity in a level of pathophysiology because aberrant NA as a vulnerability of psychotic symptoms was independent of aberrant N400 as and index of thought disturbance.