Lateralization patterns of event-related potential and performance indices in schizophrenia: relationship to clinical state and neuroleptic treatment.

In a previous study we assessed lateralization patterns of verbal stimuli processing, by means of behavioural and neurophysiological measures, in a sample of drug-free schizophrenics and one of normal controls. The main findings obtained were the following: (1) a right visual field (RVF) advantage on reaction time (RT) and late positive complex (LPC) peak of the ERPs in normal subjects but not in schizophrenics; (2) a left visual field (LVF) significant advantage on P360 and slow wave (SW) amplitude in schizophrenics but not in controls; (3) a significantly longer RT and smaller P360 and SW for RVF stimuli in schizophrenics as compared to normals; (4) a significant contralateral effect of visual field on N180 at both the left and the right parietal site in normal controls and only at the right parietal site in schizophrenics. As a further step of this investigation we re-tested 9 schizophrenics after 28 days of haloperidol treatment. The post-treatment lateralization pattern of verbal stimuli processing was characterized by a RVF advantage on LPC peak amplitude and no visual field effect on P360 and SW, resembling the normal group pattern. Moreover, the N180 amplitude was found to be reduced. Relationships between lateralization pattern and clinical picture changes induced by haloperidol treatment are discussed.