Negative difference (Nd), an ERP-marker of stimulus relevance : different lateral asymmetries for paranoid and non-paranoid schizophrenics

We studied Nd in psychotic patients with varying degrees of paranoid symptoms. Nd is an ERP measure of the difference registered by a non-attended tone and the same tone used later as a discrimination target. Methods: In a 3-tone oddball paradigm we recorded from 19 sites in 22 young healthy subjects and 28 patients with schizophrenia in a passive tone presentation and an active discrimination. Results: 1/ Nd (200-260 ms) was fronto-central and bilaterally symmetrical in healthy subjects. 2/ Paranoid patients showed a left-frontal/right temporoparietal amplitude reduction which was reversed in non-paranoid subjects, (reduced at right-frontal/left posterior sites). 3/ These asymmetries were similar but clearer when the groups were separated by active paranoid symptoms than by diagnosis. Conclusions: Thus there are functional asymmetries mediating stimulus relevance (controlled processing) in schizophrenic patients which differ from controls and differ between patients with and without active paranoid symptoms. See other reports on Nd in healthy subjects (1995), and in schizophrenia (1991 ,1996)


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