IMPAIRMENT OF EARLY CORTICAL PROCESSING IN SCHIZOPHRENIA - AN EVENT-RELATED POTENTIAL CONFIRMATION STUDY

Abnormalities of auditory information processing represent a core feat ure of schizophrenic psychopathology. Event-related potentials (ERP) p rovide an objective index of the information processing deficits assoc iated with schizophrenia and a tool for investigation of the underlyin g pathophysiology. The best established abnormality is a decrease in t he amplitude of auditory P300. In an ''oddball'' paradigm, P300 is pre ceded by a series of earlier, negative-polarity ERP components that in dex discrete, prior information-processing events. The earliest such c omponent, mismatch negativity (MMN), is elicited whenever a deviant, ' 'oddball'' stimulus interrupts a sequence of repetitive standard stimu li. MMN is generated principally within primary auditory cortex or adj acent structures on the superior temporal plane, suggesting that it in dexes the earliest cortical event in the cognitive processing of audit ory information. In the present study, MMN was studied in a group of 1 4 chronic schizophrenic subjects relative to 12 age- and IQ-matched no rmal controls in a passive auditory oddball paradigm in order to test the hypothesis that auditory information processing is impaired in sch izophrenia, even at the level of primary sensory cortex. Schizophrenic subjects showed a significant reduction in MMN amplitude relative to controls, with a trend toward a greater deficit on the left than the r ight side. The finding of impaired MMN generation in schizophrenia sug gests that information processing is impaired even at the level of aud itory cortex and that the pathophysiological processes underlying info rmation processing dysfunction in schizophrenia are widespread through out the cortex, rather than limited to high-order association cortex s uch as prefrontal or mesial temporal cortex.