Auditory event-related potential abnormalities in bipolar disorder and schizophrenia

Auditory P300 latency prolongation or amplitude reduction has been reported in patients affected by bipolar disorder and in schizophrenia. The purpose of this study was to test whether the auditory P300 and earlier event-related potential (ERP) components elicited during an auditory discrimination task could differentiate between these two disorders. Thirteen patients with manic or mixed bipolar disorder, 12 patients with schizophrenia, and 24 control subjects were evaluated. None of the subjects had a history of alcohol or substance abuse or dependence. ERPs were elicited during an auditory discrimination task in which a subject pressed a key to infrequent 1500 Hz tones interspersed amid a series of 1000 Hz tones. The amplitude and latency of N100 and P200 were measured from ERPs to non-target tones, and N200 and P300 were measured from ERPs to target tones. N100, P200 and N200 amplitudes were reduced in schizophrenia patients, but not in bipolar patients. Both bipolar disorder and schizophrenia patients showed reduced P300 amplitude and prolonged P300 latency. Amplitude reduction in the early ERP components implicates auditory processing deficits in schizophrenia. Both groups showed reductions in P300 amplitude, suggesting a disturbance of the temporal-parietal generators of this component. Prolonged P300 latency is consistent with impaired attentional processing in schizophrenia and symptomatic bipolar disorder patients.