IMPAIRED ATTENTION-DEPENDENT AUGMENTATION OF MMN IN NONPARANOID VS PARANOID SCHIZOPHRENIC-PATIENTS - A COMPARISON WITH OBSESSIVE-COMPULSIVEDISORDER AND HEALTHY-SUBJECTS

Mismatch negativity (MMN) in the deviant-minus-standard event-related potential (ERP) difference-waveform, may represent a working memory tr ace of the tone difference. Most but not all studies find MMN reduced in schizophrenic patients. This report investigates if differences may be attributable to experimental condition (diffuse vs focused attenti on), component identification (N1-like vs N2-like), topographic distri bution, and clinical condition (with/without paranoid-hallucinatory sy mptoms, PH/NP). Comparisons were made for 12 PH, 12 NP schizophrenic p atients with 13 obsessive compulsive and 25 normal control subjects. F rontal MMN reduction in schizophrenics largely resulted from an absenc e of an increase in focused attention conditions as in comparison grou ps. But there was a marked temporal activity locus in NP patients. The se features were not reflected in other components except for a visibl e but nonsignificant N1-like temporal locus in NP patients. Further, s chizophrenic patients did not show an increase in late positivity with focused attention like the comparison groups. The results show that s o-called automatic processing deficits (amount and locus of MMN) are b est seen in situations requiring the activation of controlled attentio nal processes. It is suggested that impaired processing of irrelevant stimuli and reduced frontal MMN in NP patients may reflect reduced dop aminergic responsivity. (C) 1997 Society of Biological Psychiatry.