The visual P3a in schizophrenia and bipolar disorder: effects of target and distractor stimuli on the P300.

Amplitude reduction of the P300 event-related potential has long been suggested as a marker for schizophrenia. However, recent research has shown that this reduction in the P300 amplitude is not specific to schizophrenia as it can also be observed in related illnesses such as bipolar disorder. Due to this lack of specificity the P300 elicited using traditional oddball paradigms may be a less valuable endophenotypic marker. The current study employed a cognitively demanding three-stimulus oddball paradigm to elicit the P300 to visual target and distracting stimuli. Patients with schizophrenia showed amplitude reductions of P300 components to targets, distractors and frequent stimuli. The P300 in patients with bipolar disorder was not significantly different from either group. The pattern of results may further the understanding of the nature of the impairment in schizophrenia.