FIRST-EPISODE SCHIZOPHRENIC PSYCHOSIS DIFFERS FROM FIRST-EPISODE AFFECTIVE PSYCHOSIS AND CONTROLS IN P300 AMPLITUDE OVER LEFT TEMPORAL-LOBE

Background: Schizophrenia is associated with central (sagittal) midlin e reductions of the P300 cognitive event-related potential and topogra phic asymmetry of P300, with reduced left temporal voltage. This P300 asymmetry is, in turn, linked to tissue volume asymmetry in the poster ior superior temporal gyrus. However, it is unknown whether P300 asymm etry is specific to schizophrenia and whether central and lateral P300 abnormalities are due to chronic morbidity, neuroleptic medication, a nd/or hospitalization, or whether they are present at the onset of ill ness. Methods: P300 was recorded in first-episode schizophrenia, first -episode affective psychosis, and control subjects (n=14 per group). S ubjects silently counted rare (15%) target tones (1.5 kHz) among train s of standard tones (1.0 kHz). Averages were constructed from brain re sponses to target tones. Results: Peak amplitude of P300 and integrate d voltage over 300 to 400 milliseconds were significantly different be tween first-episode schizophrenics and controls over the posterior sag ittal midline of the head. First-episode schizophrenics displayed smal ler amplitudes over the left temporal lobe than first-episode affectiv e psychotics and controls, but the groups showed no differences over t he right temporal lobe. Conclusions: Left-sided P300 abnormality in fi rst-episode schizophrenia relative to first-episode affective psychosi s and controls suggests that P300 asymmetry is specific to schizophren ic psychosis and present at initial hospitalization. This P300 asymmet ry suggests left temporal lobe dysfunction at the onset of schizophren ia.