REPLICATION OF A P50 AUDITORY GATING DEFICIT IN AUSTRALIAN PATIENTS WITH SCHIZOPHRENIA

Schizophrenic patients reportedly have a deficit in the control of sen sitivity to auditory stimuli as shown by the P50 auditory evoked poten tial wave in a conditioning-testing paradigm that measures suppression of response to a repeated stimulus. Although this finding has been re plicated by several US laboratories, one European group has not found differences between schizophrenic patients and normal control subjects . In the present study, investigators in the Schizophrenia Research Ce nter at the Prince of Wales Hospital in Sydney, Australia, selected 22 normal control subjects, II acutely ill schizophrenic inpatients, and 11 clinically stable schizophrenic outpatients. Both schizophrenic gr oups were treated with similar doses of classical neuroleptic medicati ons. Evoked potentials were recorded by an investigator from the US la boratory that initially reported the difference; five averages, each t he response to 32 stimulus pairs, were recorded from each subject. The normal control subjects demonstrated significantly more suppression o f the P50 response to the repeated stimuli than the schizophrenic grou ps, as previously reported. There were no significant changes in the s uppression measure over the five trials. The suppression of the P50 wa ve by schizophrenic outpatients was somewhat greater than that by schi zophrenic inpatients, but both schizophrenic groups had decreased supp ression, compared with the normal subjects. The mean P50 suppression f or five averages was successfully used in a logistic regression to cla ssify subjects as normal or schizophrenic. This method was more accura te than attempts to classify subjects with only one average. The mean amplitude of the initial conditioning response did not differ between groups. Schizophrenic patients had slightly shorter mean latencies. Th ere was no direct relationship of P50 suppression to measures of clini cal psychopathology.