A FUZZY CLUSTERING APPROACH TO STUDY THE AUDITORY P50 COMPONENT IN SCHIZOPHRENIA

We have recently provided evidence that selective evoked response aver aging based on a fuzzy clustering approach is a useful way to increase the signal-to-noise ratio, particularly when recording low-amplitude components, such as the auditory P50. We have also reported that, when stimuli are delivered in pairs (S-1 followed by S-2) with a short int erstimulus interval, the first stimulus (S-1) results in synchronizati on of the EEG producing a large-amplitude evoked response, whereas the second stimulus (S-2) causes phase opposition resulting in a lower am plitude average evoked response. In the current study we reanalyzed da ta previously obtained from 13 normal volunteers and 17 chronic schizo phrenia patients. Our results show that the partial EPs corresponding to the S-1 stimulus are highly synchronized in normal subjects but not in schizophrenia patients. However, such a synchronization is not pre sent after delivery of the S-2 stimulus, neither in normal controls no r in patients. These findings are in agreement with previous reports o f decreased amplitude of the S-1 response without a significant furthe r decrease in the amplitude of the S-2 response in schizophrenia patie nts. (C) 1997 Elsevier Science Ireland Ltd.