Evoked potential variation in schizophrenic subgroups.

Unmedicated chronic schizophrenic inpatients and nonpsychotic controls were tested in a paradigm designed to elicit habituated event-related potentials (ERPs) to auditory stimuli. Analysis of Variance of the ERP components recorded at bilateral frontal (F1 and F2) and temporal (T3 and T4) scalp leads revealed significant decreases in N1 component amplitudes in both frontal leads in the schizophrenic subjects. P2 and N2 amplitudes also tended to be smaller at frontal leads in the schizophrenic subjects, but these differences were not found to be statistically significant overall. The schizophrenic subjects were assigned to diagnostic subgroups following administration of the Diagnostic Interview Schedule, the Maine Paranoid Scale, and the Scale for the Assessment of Negative Symptoms. Subjects meeting DSM-III criteria for paranoid schizophrenia were assigned to one subgroup (PS subgroup), and those meeting DSM-III criteria for residual or undifferentiated schizophrenia were assigned to another subgroup (RS subgroup). The Analysis of Variance of the N1 amplitude measures was repeated with subgroup diagnosis as a factor, revealing significant decreases in N1 amplitude in the PS, but not the RS, patients. Patients in the PS subgroup were found to differ significantly from those in the RS subgroup on this ERP measure, as well as from controls. These results suggest that subgroup differences exist within the schizophrenic population that are reflected in differential changes in ERP morphology.