Visual evoked potentials in schizophrenia. Intensity effects and hemispheric asymmetry

Visual evoked potentials (VEP) to different flash intensities were recorded at a central site (Cz) plus at homologous temporal and occipital locations in normal and unmedicated schizophrenic subjects. Schizophrenic patients showed an hemisphere asymmetry of the P100-N120 peak-trough amplitude with smaller left but larger right hemisphere amplitudes than normal. Further, two subgroups of patients were found with abnormalities lateralized to the left hemisphere. One group was found to have abnormal P100 amplitude-intensity patterns at the left temporal site while the other group showed deviant N120 amplitude-intensity patterns at the left occipital location. The clinical significance of these results can be seen in the higher nuclear schizophrenia (PSE-CATEGO) scores in the left temporal subgroup and the higher hypomania and situational anxiety scores in the left occipital group. Patients also showed slower than normal P100 and N120 peak latencies.