AUDITORY EVENT-RELATED POTENTIAL (ERP) AND DIFFERENCE-WAVE TOPOGRAPHYIN SCHIZOPHRENIC-PATIENTS WITH WITHOUT ACTIVE HALLUCINATIONS AND DELUSIONS - A COMPARISON WITH YOUNG OBSESSIVE-COMPULSIVE DISORDER (OCD) AND HEALTHY-SUBJECTS/

Event-related potentials (ERPS) in schizophrenics have been reported t o show a reduced P3 on the left and less frontal mismatch negativity ( MMN). But the specificity of such findings to component, its locus, th e type of eliciting event and patient group remains uncertain. Hence, we examined ERP topography for P3, N2 and 3 precursor peaks according to stimulus (3-tone oddball), attention condition (diffuse/focused) an d four types of difference-waves. We contrasted 24 healthy and 13 OCD subjects with schizophrenic patients with high versus low ratings of a ctive delusions and hallucinations (12 paranoid-hallucinatory, PH; 12 nonparanoid, NP). P3 peaks were delayed and reduced in NP and PH group s. Midline peaks were usual in focused attention and a right bias in d iffuse attention. P3 responses to irrelevant standards remained latera l in NP and small in OCD patients. All showed a small left and anterio r bias in the P3-like peak in difference-waves. Mismatch negativity wa veform (MMN) peaks shifted to the right in OCD, to both sides in PH an d posteriorly in NP patients. Frontal processing negativity was biased to the left (early) in NP and to the right (late) in PH groups. Early peak topography reflected some later changes (e.g. PH and NP groups; Pi-like peak, right bias absent; N1-like peak depressed and widely dis tributed: NP group, P2-like peak smaller on the left). In OCD patients , peak latencies were topographically undifferentiated (Pi, P2) or del ayed (N2). The OCD group showed an unusual regional allocation of proc essing effort. Before 200 ms frontocentral activity was more widesprea d in PH and NP groups. Lateralization of negativity in target- and non target-derived difference-waves may reflect differential disruption of the frontal-temporal dialogue in registering important vs unimportant features. NP patients, in particular, treated irrelevant stimuli anom alously.