P300 topographic asymmetries are present in unmedicated schizophrenics.

Our laboratory has repeatedly found a left < right auditory P300 temporal lobe topographic asymmetry in right-handed, medicated schizophrenics. To determine whether this asymmetry was attributable to the effects of antipsychotic medications, we collected auditory "odd-ball" P300 event-related potentials from 14 right-handed, unmedicated schizophrenics (withdrawn from medication for an average of 21 days) and 14 right-handed, normal controls. Analysis of normalized P300 amplitudes showed a statistically significant difference in the voltage distributions between groups (a group by temporal electrode site interaction) that was consistent with a left < right temporal voltage asymmetry in schizophrenics but not in the normal controls. We conclude that P300 topographic asymmetries are present in unmedicated schizophrenics. These data are compatible with the growing body of data suggesting left temporal lobe structural abnormalities in schizophrenia.