P300 abnormality in schizophrenic subtypes.

P300 and other long latency event-related potentials were recorded in 65 schizophrenic subjects and results were compared to findings in 119 healthy controls. Highly significant differences in P300 latency and amplitude were found between the two groups. Forty six per cent of schizophrenics had P300 latency more than two standard deviations longer than the mean for controls, 35% had a P300 amplitude smaller than the mean for controls by the same amount, and 24% were more than two standard deviations outside the mean for controls on both measures. These differences were independent of chronicity of illness, clinical subtype, family psychiatric history or the effects of neuroleptic medication. They confirm that P300 abnormality is present as a stable trait in a high proportion of schizophrenics. The status of abnormal P300 as a biological vulnerability factor for major mental illness is discussed.