P300 subcomponent abnormalities in schizophrenia: II. Longitudinal stability and relationship to symptom change.

BACKGROUND: Reduced amplitude of the P300 event-related brain potential (ERP) is a robust finding in schizophrenia. It remains unclear whether this represents a state or trait abnormality. We previously reported reductions of specific subcomponents of the auditory oddball P300 that were independent of acute symptomatology and were differentially associated with gender and deficit/nondeficit subtype. To clarify the state vs. trait nature of these abnormalities, we reassessed a subset of these patients after a minimum interval of 1 year following initial study.
METHODS: Auditory P300 ERPs were obtained from 18 patients at two time points and compared to baseline normative data recorded from 48 controls. Five P300 subcomponents were identified using current source density measures: frontal (P3f), bilateral parietal (P3pL, P3pR), and bilateral temporal (P3tL, P3tR).
RESULTS: Patients exhibited reduced P300 amplitudes at baseline, including specific reductions of left temporal and right parietal subcomponents. There were no significant changes in P300 amplitudes over time, despite significant improvement in symptomatology, and the parietal subcomponent exhibited persistent impairment. There was, however, a trend toward normalization of the left temporal subcomponent that correlated with change in Brief Psychiatric Rating Scale. There was also a highly significant inverse relationship between changes in frontal P300 subcomponent amplitude and severity of auditory hallucinations (r = -.76).
CONCLUSIONS: The findings support the overall longitudinal stability of P300 deficits in schizophrenia, though there is some state-dependent modulation of these deficits. The relationship between the frontal P300 and hallucinations is consistent with both the cognitive orienting function of this subcomponent and the role of the anterior cingulate as a hypothesized generator of this ERP activity.