Multiple site evaluation of P50 suppression among schizophrenia and normal comparison subjects.

Normally, when two brief, non-startling auditory stimuli are presented 500 ms apart, with long (e.g., 10 s) interpair intervals, the positive potential occurring approx. 50 ms after the first stimulus (P50) is relatively large, and the P50 to the second stimulus is smaller. In schizophrenia patients, however, the P50 to the second stimulus is larger than normal. In this study, 36 schizophrenia and 36 normal comparison subjects were tested in a two-click paradigm. Data were recorded from six electrode locations (F3, Fz, F4, C3, Cz, C4). The results support the hypothesis that schizophrenia patients have poor P50 suppression that is not an artifact of differential P50 wave morphology or differences in the number of usable trials between groups. In addition, the vertex location alone (Cz) was equal to, if not better than, any combination of sites for differentiating between groups. These results support the use of the Cz site alone in most investigations of P50 suppression deficits among schizophrenia spectrum patients. Further work investigating the neuropathological correlates of poor P50 suppression among schizophrenia patients by recording from multiple electrode locations, however, could be helpful.