P300 topography differs in schizophrenia and manic psychosis.

BACKGROUND Overall and left temporal scalp area reductions of P300 have been demonstrated in schizophrenia. P300 amplitude and topography in psychotic affective disorder, a crucial comparison in assessing the specificity of P300 abnormalities to schizophrenia, are not well studied. METHODS P300 was recorded from 35 schizophrenic, 20 psychotic manic, and 30 control subjects. All were right-handed men. RESULTS P300 was reduced in both psychotic groups relative to control subjects. Anteroposterior P300 topography differed between patient groups, with schizophrenic subjects showing posterior reduction and bipolar subjects showing anterior reduction. Schizophrenic subjects showed an abnormal asymmetry, with smaller P300 over the left temporal scalp site than the right. Both bipolar and control subjects showed a left greater than right asymmetry. CONCLUSIONS Widespread auditory P300 reductions were present in schizophrenia and bipolar disorder with psychosis, but subtle topographic differences were present in the two diseases. Although unequivocal knowledge of neural generators cannot be derived from topography alone, differences in topography imply different generator configurations. Based on previous studies, the posterior P300 reductions in schizophrenia may reflect abnormalities of a generator located in the left superior temporal gyrus. The frontal reductions in bipolar psychosis may reflect abnormalities in a hypothetical frontal generator, consonant with reports of altered frontal lobe function in mania.