P300 ASYMMETRIES IN SCHIZOPHRENIA REVISITED WITH REFERENCE-INDEPENDENT METHODS

Evidence of hemispheric asymmetries in schizophrenia has been reported from different research areas. Asymmetries in evoked potential P300 t opography are still controversial because of inconsistent findings. In the present study, previous results of abnormal lateralization of P30 0 were replicated in stabilized residual schizophrenic patients. Audit ory P300 was recorded during an oddball task in which subjects detecte d rare target stimuli. Schizophrenic patients had the P300 peak shifte d to the right hemisphere and differed significantly from age- and sex -matched normal control subjects who had left-lateralized P300 peaks. A comparison of different methods of assessment and analysis of the to pographical features of the P300 electric fields showed that the extra ction of reference-independent descriptors of P300 topography is a rel iable and sensitive method for statistical handling of the maps. The r esults suggest left hemispheric dysfunction during cognitive tasks in a subgroup of schizophrenic patients. Inconsistencies between previous studies are likely to be due to heterogeneous patient groups, which m ay have included patients in an acute schizophrenic episode or patient s in clinical remission. Investigation of the clinical meaning of P300 alterations requires careful psychopathological definition of the pat ient groups.