First-episode schizophrenic psychosis differs from first-episode affective psychosis and controls in P300 amplitude over left temporal lobe.

Schizophrenia is associated with central (sagittal) midline reductions of the P300 cognitive event-related potential and topographic asymmetry of P300, with reduced left temporal voltage. This P300 asymmetry is, in turn, linked to tissue volume asymmetry in the posterior superior temporal gyrus. However, it is unknown whether P300 asymmetry is specific to schizophrenia and whether central and lateral P300 abnormalities are due to chronic morbidity, neuroleptic medication, and/or hospitalization, or whether they are present at the onset of illness. P300 was recorded in first-episode schizophrenia, first-episode affective psychosis, and control subjects (n = 14 per group). Subjects silently counted rare (15%) target tones (1.5 kHz) among trains of standard tones (1.0 kHz). Averages were constructed from brain responses to target tones. Peak amplitude of P300 and integrated voltage over 300 to 400 milliseconds were significantly different between first-episode schizophrenics and controls over the posterior sagittal midline of the head. First-episode schizophrenics displayed smaller amplitudes over the left temporal lobe than first-episode affective psychotics and controls, but the groups showed no differences over the right temporal lobe. Left-sided P300 abnormality in first-episode schizophrenia relative to first-episode affective psychosis and controls suggests that P300 asymmetry is specific to schizophrenic psychosis and present at initial hospitalization. This P300 asymmetry suggests left temporal lobe dysfunction at the onset of schizophrenia.