Oades, R.D., Zerbin, D., Dittmann-Balcar, A. & Eggers, C. (1996). Auditory event-related potential (ERP) and difference-wave topography in schizophrenic patients with/without active hallucinations and delusions: a comparison with young obsessive-compulsive disorder and healthy subjects. Int. J. Psychophysiol., 22, 185-214. (request a copy) . (view) .

Event-related potentials (ERPs) in schizophrenics have been reported to show a reduced P3 on the left and less frontal mismatch negativity. But the specificity of such findings to component, its locus, the type of eliciting event and patient group remains uncertain. Hence, we examined ERP topography for P3, N2 and 3 precursor peaks according to stimulus (3-tone oddball), attention condition (diffuse/focused) and four types of difference-waves (Mismatch negativity, Processing negativity, Negative difference (Nd) and the 'Goodin-Waveform').

We contrasted ERPs in a 3-tone oddball task-form in 24 healthy (mean 18.5y of age) and 13 OCD (mean age 16.3 y) subjects with schizophrenic patients with high versus low ratings of active delusions and hallucinations (12 paranoid-hallucinatory, PH [mean age 18.5y]; 12 nonparanoid, NP [mean age 18.9y])

1. P3 peaks were delayed and reduced in NP and PH groups. Peaks in the midline were usual in the focused Figure 2attention condition, but a right bias in diffuse attention (passive presentation).
2. P3 responses to irrelevant non-targets remained lateralised in NP, and small in OCD patients. All showed a small left and anterior bias in the P3-like peak recorded after subtraction in the difference waves.
3. Mismatch negativity (MMN) peaks shifted to the right in OCD, laterally to both sides in PH and more posteriorly in NP patients.
Figure 24. Frontal processing negativity was biased to the left (early) in NP and to the right (late) in PH groups.
5. Early peak topography in the difference waveforms reflected some of these later changes (e.g., for PH and NP groups the normal right bias in the P1-like peak was absent; the N1-like peak was reduced and widely distributed: for the NP group, the P2-like peak appeared smaller on the left).
6. In OCD patients, the peak latencies were topographically undifferentiated for P1 and P2, or delayed in the case of the N2 component.

The OCD group showed an unusual regional allocation of processing effort.
B) Before 200 ms, fronto-central activity was more widespread in both the PH and NP groups.
C) NP patients, in particular, treated irrelevant stimuli anomalously.
D) Lateralisation of negativity in target- and nontarget-derived difference waves may reflect differential disruption of the frontal-temporal dialogue in registering important vs. unimportant features. Indeed, the apparent left/right differences of negative difference (Nd) or processing negativity amplitude may not so much reflect amplitude differences as a delayed latency over left frontal areas in PH and over the right frontal areas in NP patients with schizophrenia.