Evoked potential topography in unmedicated and medicated schizophrenics.

The main purposes were to determine whether: (1) evoked potential (EP) topography differs from normal in schizophrenics; (2) EP topography is altered by psychotropic drugs. Unmedicated (n = 72) and medicated (n = 57) schizophrenics were compared with age- and sex-matched non-patients and with one another. EPs to left and right median nerve, visual pattern and auditory stimuli were recorded from 15 leads. EP data were reduced by principal component analysis (PCA) of EP waveforms, with separate PCAs for later and earlier poststimulus times; 32 factors were extracted. Factor scores, based on factor structure of 195 non-patients, were computed for all subjects. Topographic effects were evaluated by ANOVAs on Z-transformed factor scores. The results were: (1) topographies differed between groups in about one-third of the factors, but variables yielding effects differed between comparisons; (2) topographic differences from normal in unmedicated patients converged at left temporoparietal (higher in schizophrenics) and right fronto-central-temporal areas (lower in schizophrenics); (3) similar convergence was absent in medicated patients; (4) most medicated vs unmedicated patient topographic differences persisted in groups matched for psychopathology. Results appear consistent with "focal cortical arousal" of the left posterior quadrant in schizophrenics (Morihisa and Duffy, 1986) and suggest that medication alters EP topography.