508. How specific are deficits in generation of mismatch negativity to schizophrenia?

Abstract

Mismatch negativity (MMN) is a preattentive event-related potential that elicited by infrequent deviant stimuli presented among frequently presented standard stimuli. It manifests the automatic detection of stimulus deviance and indexes the functioning of echoic memory—a simple, working’ memory system at the level of the auditory sensory cortex. Animal and human data indicate an involvement of NMDA-receptors in MMN generation. In schizophrenia deficits in MMN generation and echoic memory have repeatedly been demonstrated. The specificity of this deficit to schizophrenia has not been established. We are conducting a study comparing MMN generation in healthy controls and in age-matched patients with a diagnosis of schizophrenia or schizoaffective disorder, bipolar disorder and major depression. Patients are matched on duration of illness. MMN is recorded both in a duration deviance and pitch deviance condition. Preliminary analyses of 53 subjects (Healthy controls N = 14; schizophrenic/schizo-affective patients N = 21; bipolar patients N = 9; depressed patients N = 8) demonstrate the greatest deficit in MMN generation in both conditions in patients with schizophrenia or schizoaffective disorder. Only schizophrenic/schizoaffective patients showed significantly smaller MMN than normal controls. The difference was more pronounced in the duration deviance condition. Patients with bipolar disorder or major depression demonstrated slight, but not significant reductions of MMN generation compared to normal controls. Our data suggest a relative specificity of MMN deficits for schizophrenia. Given the evidence that MMN deficits reflect deficient NMDA-related neurotransmission our findings are consistent with specific abnormalities in this neurotransmitter system in schizophrenia.