P300 responses to novel auditory stimuli in hospitalized schizophrenic patients.

The authors studied the scalp topography of P300 responses to novel auditory stimuli and its relationship to negative symptoms in medication-free hospitalized schizophrenic patients. Schizophrenics (n = 12), patients with major mood disorders (n = 13), and 17 non-ill controls (all men) responded to rare target tones while ignoring background tones and rare novel stimuli. P300 responses were identified from plots of global field power (GFP), a measure of potential variability over the entire electrode set. Multivariate analysis revealed that P300 responses to novel stimuli were faster (p < 0.003), larger (p < 0.001), and distributed more centrally than parietally (p < 0.001) than those to targets, but this central augmentation was significantly (p < 0.04) less in schizophrenics. Compared to controls, P300 amplitude (p < 0.05) and GFP (p < 0.02) after novel stimuli were reduced relative to target responses in schizophrenics. Negative symptoms were inversely correlated with P300 amplitude (P = 0.013) and GFP (p < 0.04) across conditions and with P300 GFP in the novel condition (p = 0.01), but did not predict topography of responses to novel stimuli. The findings were consistent with but not conclusive evidence of prefrontal impairment in the schizophrenics subjects. Methodological issues and conflicts with other reports are discussed.