Abnormalities of auditory event-related potentials in schizophrenia prior to treatment.

Background: P300 amplitude reduction is a consistent finding in schizophrenic patients, but it is unclear if this abnormality predates neuroleptic treatment or is present at onset of illness.

Methods: Auditory event-related potentials (ERPs), during a standard oddball paradigm, were recorded from 45 neuroleptic-naive schizophrenics, 56 drug-free, previously treated schizophrenics, and 73 healthy normal controls. Forty-seven of the schizophrenic subjects had their first episode within the past year.

Results: N200 amplitude did not differ among groups. P300 amplitude was significantly smaller in both neuroleptic-naive and previously treated schizophrenic groups compared to the control groups. There were no significant differences between the two schizophrenic groups in P300 amplitude. N200 and P300 latency were prolonged in previously treated schizophrenics compared to neuroleptic-naive schizophrenics and normal controls.

Conclusions: The present study suggests that ERP abnormalities, especially P300 amplitude reduction, are already present prior to the administration of neuroleptic medication in the earliest stage of schizophrenia.