Lateralized neuroleptic-induced side effects are associated with asymmetric visual evoked potentials

Recent studies suggest that neuroleptic drugs may have an asymmetric effect on the two cerebral hemispheres. This effect is reflected by emergence of drug-induced lateralized extrapyramidal side effects and by dose-related alterations in electrophysiological asymmetries. The present study examined the hypothesis that asymmetry of visual evoked potentials (VEPs) is associated with lateralized appearance of neuroleptic-induced parkinsonism or tardive dyskinesia (TD). The asymmetry of the amplitudes of later VEP components was significantly higher in patients with lateralized side effects (n = 8) than in patients with symmetrical side effects (n = 6) or free of extrapyramidal side effects (n = 11). The possibility that VEP asymmetry reflects the differential degree to which the two hemispheres are affected by medication is discussed.