Replication of an evoked potential study of lateralized hemispheric dysfunction in schizophrenics.

Visual (VEP) and auditory (AEP) evoked potentials (EPs) were measured to replicate previous findings concerning lateralized hemispheric dysfunction in chronic schizophrenic patients in a new sample. Measures of EP waveform stability (Zr') showed greater hemispheric asymmetry in 26 unmedicated chronic schizophrenics than in 26 matched nonpatients, and relatively lower left and right hemisphere values in schizophrenics. Similar hemispheric differences were not found between medicated patients and matched nonpatients; medication was associated with higher left and lower right hemisphere stability. EP amplitudes were lower with medications, the lowest amplitudes found in patients receiving nonphenothiazine or nonpiperazines as opposed to phenothiazine-piperazine drugs. Medications were associated with amplitude asymmetries not observed in unmedicated patients. This study confirms greater than normal hemispheric asymmetry of VEP and AEP waveshape stability measures in chronic schizophrenics, and lower left than right hemisphere stability suggesting left hemisphere dysfunction. Alteration of EP asymmetries by antipsychotic medications suggests that medication effects may obscure evidence of lateralized dysfunction in schizophrenics.