P3 in Schizophrenia Is Affected by Stimulus Modality, Response Requirements, Medication Status, and Negative Symptoms

• Eighteen schizophrenics who were not taking medication, 13 schizophrenics who were taking medication, and 37 agematched controls were tested with event-related potential paradigms designed to elicit P₃ response automatically or effortfully (ie, with a choice reaction time task). Electroencephalograms were recorded from the 19 standard 10-20 electrode sites. Compared with controls, both groups of schizophrenics had reduced P₃ amplitudes for both effortful and automatic paradigms. P_, latencies were delayed relative to controls for the medicationtaking schizophrenics in the effortful paradigms. Negative symptoms derived from the Brief Psychiatric Rating Scale within 1 week of event-related potential testing correlated negatively with both auditory and visual P₃ amplitude in the subjects who were not taking medication. There was no evidence that P₃ is smaller over left temporal electrode sites in schizophrenics, as has been reported by others. P₃ amplitude reduction in schizophrenia is a robust psychobiological phenomenon that is present regardless of medication status or task demands.