Impairment of an event-related potential correlate of memory in schizophrenia: Effects of immediate and delayed word repetition

Objective: We investigated the nature of the memory impairment in schizophrenia using an event-related potential (ERP). Methods: Visual ERPs were recorded while 20 schizophrenics and 20 controls performed semantic categorization tasks with incidental word repetitions. Participants responded to occasional target words. Half of the non-target words were repeated immediately after initial presentation (lag 0) or after 5 intervening words (lag 5). Results: In both groups, ERPs to words at lag 0 were more positive than those to non-repeated words, though this positive-going effect was attenuated in the schizophrenics, especially around 400-500 ms. The effect at lag 5 was smaller and shorter than that at lag 0 but was comparable between groups. Attenuation of the N400 peak occurred for word repetition at lag 0 in controls but not in schizophrenics, whereas a peak increment in the late positive component induced by word repetition at both lags was observed in both groups. Conclusions: Findings indicate that patients with schizophrenia have a deficit in a brain process modulating ERP correlates of memory, when words are repeated immediately. This deficit might be related to an abnormal N400 priming effect in schizophrenia.