Auditory P300 amplitude as a state marker for positive symptoms in schizophrenia: cross-sectional and retrospective longitudinal studies

The amplitude of the P300 component of the auditory event-related brain potential (ERP) is consistently reduced in schizophrenia. To determine whether this P300 abnormality can be used as a state marker to reflect the severity of symptoms, we examined both cross-sectionally and longitudinally the relationship between auditory P300 amplitude and symptom severity in patients with schizophrenia. For the cross-sectional study, ERP was elicited by an auditory oddball paradigm, and symptom severity was quantitatively measured by means of the Positive and Negative Syndrome Scale in 93 patients with schizophrenia or schizophreniform disorder (DSM-III-R). For the longitudinal study, ERP and psychopathology measured twice at an average interval of 238 days for 20 patients were retrospectively analyzed. The cross-sectional data showed that P300 amplitude correlated negatively with the positive but not with the negative syndrome scale score. The longitudinal data also showed a significant negative correlation between changes in P300 amplitude and in the positive syndrome scores of the first and second tests. In particular, P300 amplitude recorded at the left, but not right, posterior temporal region significantly correlated with the positive syndrome in both the cross-sectional and longitudinal studies. These findings support the hypotheses that auditory P300 amplitude recorded in the left hemisphere can be used as a state marker to reflect the severity of the positive symptoms and that the positive symptoms may be caused by a possible left-hemisphere deficit in schizophrenia. (C) 2002 Elsevier Science B.V. All rights reserved.