Electrophysiological Evaluation of Cognitive Functions (Perception, Language, and Memory) in Schizophrenia

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In order to examine the pathophysiology of schizophrenia observed in the domains of cognitive functions such as perception, thinking (language), and memory, we devised a new experimental paradigm using a visual event-related brain potential (ERP). The paradigm consisted of two semantic categorization tasks : (1) word task (WT) to examine semantic processing of word and (2) repetition task (RT) to examine memory processing of word.In the first study, ERPs for WT and RT were recorded from 20 normal volunteers. NA potentials for each task were extracted from ERPs by a subtraction procedure originally reported by Ritter et al.in 1982. NA for WT comprised two negative major peaks, although the second NA peak was absent for the unpronounceable letters. These suggest that the first and second NA peaks represent a pattern recognition and an additional processing after pattern recognition, respectively. Since the second peaked at around 400 msec after stimuli and was absent of unpronounceable letters, it corresponds to N400 potential, which reflects semantic processing of word. In the RT,amplitude of N400 as the second NA peak was reduced by word repetition. Therefore, our experimental paradigm enables us to evaluate a pattern recognition, semantic processing, and semantic memory.In the second study, original ERP waveforms of WT and RT were compared between 10 remitted patients with schizophrenia and 20 matched normal controls. The schizophrenic patients showed a retardation of the first and second NA peaks, and a lack of word-repetition effect on the second NA peak. These abnormalities indicate a slowed processing in pattern recognition and semantic processing, and also a disturbance of utilizing semantic memory in schizophrenia. We believe that these abnormalities would be core deficits of schizophrenic vulnerability, which determines occurrence of psychotic symptoms.