Mismatch negativity and N2b attenuation as an indicator for dysfunction ofthe preattentive and controlled processing for deviance detection in schizophrenia: a topographic event-related potential study

The present study compares the amplitudes and topographic patterns of misma tch negativity (MMN) and N2b in schizophrenic patients and normal controls. Twenty-one schizophrenic outpatients and 19 normal volunteers participated in the study. Event-related potentials (ERPs) were recorded in a selective attention task. During the task, subjects were required to focus on one ea r, counting deviant stimuli, those deviating in duration from a sequence of standard stimuli. MMN was significantly attenuated in the schizophrenics a s compared with the normals in the frontocentral regions. In addition to MM N, the N2b amplitude was also reduced, which showed a significant correlati on with the MMN amplitude in the schizophrenics. The late negativity elicit ed by the deviant stimuli in the unattended condition showed different topo graphical features between the groups. Whereas the normals showed a lateral ized distribution with an ear-related asymmetry, similar to that of the N2b , the schizophrenics showed a frontal dominance, coinciding with the sustai ned negativity reported by Naatanen et al. (1982), which reflects the autom atic preparation for detecting possible subsequent stimulus changes. The am plitude of the sustained negativity was significantly correlated with the p erformance level in the schizophrenics. The results indicated that although both preattentive and controlled processings are impaired, schizophrenic p atients, presumably due to the deficient controlled processing, owe much to automatic processing in the deviant stimulus detection process. (C) 1999 E lsevier Science B.V. All rights reserved.