Ina Grzella

Impaired attention-dependent augmentation of MMN in nonparanoid vs paranoid schizophrenic patients: A comparison with obsessive-compulsive disorder and healthy subjects

Mismatch negativity (MMN), in the deviant-minus-standard event-related potential (ERP) difference-waveform, may represent a working memory trace 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 attention), component identification (N1-like vs N2-like), topographic distribution, and clinical condition (with/without paranoid-hallucinatory symptoms, PH/NP). Comparisons were made for 12 PH, 12 NP schizophrenic patients with 13 obsessive compulsive and 25 normal control subjects. Frontal MMN reduction in schizophrenics largely resulted from an absence of an increase in focused attention conditions as in comparison groups. But there was a marked temporal activity locus in NP patients. These features were not reflected in other components except for a visible but nonsignificant N1-like temporal locus in NP patients. Further, schizophrenic patients did not show an increase in late positivity with focused attention like the comparison groups. The results show that so-called automatic processing deficits (amount and locus of MMN) are best seen in situations requiring the activation of controlled attentional processes. It is suggested that impaired processing of irrelevant stimuli and reduced frontal MMN in NP patients may reflect reduced dopaminergic responsivity.

A topographic event-related potential follow-up study on `prepulse inhibition' in first and second episode patients with schizophrenia

Dopamine agonists impair and antagonists normalize prepulse inhibition (PPI) of startle and gating of the P50 event-related potential (ERP), but the within-subject effect of treatment on impaired gating in schizophrenia has not been studied. We report the first results of a longitudinal study using PPI of ERPs as a measure of sensory gating in an auditory Go/NoGo discrimination. After admission and approximately 3 months later, at discharge, 15 patients with schizophrenia performed a discrimination between a 1.4 kHz target tone and an 0.8 kHz non-target tone with no prepulse, or with a prepulse at 100 ms or 500 ms before either tone. ERPs were recorded from 19 sites. Healthy subjects were studied twice, with 3 months between sessions. PPI of the P50 peak in the 100-ms condition was reduced in patients on admission. At discharge, decreased negative symptoms correlated with enhanced P50-PPI at frontocentral sites. After treatment increased N100-PPI at centrotemporal sites correlated with fewer positive symptoms. At frontal sites in the 100-ms condition, the initially small difference of non-target minus target P300 amplitudes increased as negative symptoms decreased. It is concluded that weak auditory prepulses interfere with early auditory stimulus processing (P50), channel selection (N100) and selective attention (P300). Gating of these stages of processing is impaired in psychotic patients and treatment tends to normalize gating in tandem with improvements of different types of symptoms.