The correlation between positive symptoms and left temporal event-related potentials in the P300 time window is auditory specific and training sensitive

One of the strongest correlations found between clinical symptoms and a biological index is that between the severity of positive symptoms of schizophrenia and the amplitude of the event-related potential (ERP) in the time window of the P300 deflection at left temporal scalp sites. The functional significance of the ERP component at stake is yet unknown. The present study aims at addressing this issue by testing whether or not the correlation a) is found in both the auditory and the visual modality, b) is restricted to the time window of the P300 deflection, and c) is stable over time. 12 patients suffering from schizophrenia were recorded 6 times at two month intervals in two oddball protocols, an auditory and a visual one. The correlation between the scores for the thought disturbance cluster of the PANSS (a cluster including most positive symptoms, i.e., conceptual disorganization, unusual thought content, grandiosity and hallucinations) and the P300 amplitude at left temporal sites was found 1) to occur only in the auditory modality, which, together with the late timing of the component, constrains its functional significance, 2) to appear in a time window adjacent to that of the P300 including at additional electrode sites, which would have to be confirmed by further studies, 3) to vanish along with the repetition of the recording sessions, which suggests that it is related to a processing difficulty that disappears with training.