The P50 component of the auditory evoked potential and subtypes of schizophrenia.

Decreased amplitude of the P50 component of the averaged evoked potential has been reported in schizophrenic patients. In an attempt to determine the relationship of this decrease to subtype diagnosis, we compared P50 amplitudes in 24 neuroleptic-free schizophrenic patients with paranoid (n = 13) versus nonparanoid (n = 11) subtype diagnoses. Eleven normal subjects and 11 cocaine users served as control groups. The schizophrenic patients were studied again after they had been treated with neuroleptics for 2 weeks. The control groups were studied again at least 2 weeks later. At baseline, the nonparanoid patients had significantly lower P50 amplitudes than did the normal subjects. The paranoid patients did not differ from the normal control subjects. The cocaine users had significantly decreased P50 amplitudes as compared with the normal control subjects. Neuroleptic treatment had no effect on P50 amplitudes in the paranoid patients but normalized amplitudes in the nonparanoid patients. The data suggest that P50 measurements may be useful in identifying subtypes of schizophrenia.