NEGATIVE DIFFERENCE (ND), AN ERP MARKER OF STIMULUS RELEVANCE - DIFFERENT LATERAL ASYMMETRIES FOR PARANOID AND NONPARANOID SCHIZOPHRENICS

We studied Nd in psychotic patients with varying degrees of paranoid s ymptoms. Nd is an ERP measurement of the difference in the way a nonat tended tone is registered and the way the same tone is registered when used later as a discrimination target. In a three-tone oddball paradi gm with passive-tone presentation and active discrimination, we record ed from 19 sites in 22 young healthy subjects and 28 schizophrenics. N d (200-260 ms) was bilaterally symmetrical in healthy subjects. Parano id patients showed a left frontal/right temporoparietal amplitude redu ction which was reversed in nonparanoid subjects (reduced at right fro ntal/left posterior sites). These asymmetries were clearer when the gr oups were separated according to active paranoid symptoms rather than by diagnosis. There would therefore seem to be functional asymmetries mediating stimulus relevance in schizophrenics which differ from contr ols and differ between patients with and without active paranoid sympt oms.