First-Episode Schizophrenic Psychosis Differs From First-Episode Affective Psychosis and Controls in P300 Amplitude Over Left Temporal Lobe

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Abstract
SINCE NEURAL activity is electrical, processing of discrete stimuli by the brain can be visualized in the electroencephalogram. These event-related potentials (ERPs) are early and sensory in nature, affected by the physical characteristics of the stimuli, or later and cognitive in nature, reflecting attention-related higher-order analyses. Cognitive ERPs have been used to examine information-processing abnormalities in schizophrenia. One particular ERP, P300, has received a great deal of interest. P300 is a positive wave that occurs about 300 milliseconds after an unusual or task-relevant stimulus that is detected, counted, or otherwise processed (for a review of factors affecting P300 amplitude, see Johnson1). Although the exact cognitive processes underlying P300 are unknown, Donchin2,3 has conceptualized P300 as the physiological correlate of updating a cognitive hypothesis, or working memory update of what is expected in the environment. P300 can be elicited by auditory, visual, and somatosensory stimulation, but most studies in schizophrenia have examined the auditory-elicited P300. Numerous studies using midline electrode sites and an "oddball task" (detecting rarely presented target stimuli from among standards) have shown that decrement in auditory-elicited P300 amplitude in schizophrenia is robust.4,5