Topographic differences between normals and schizophrenics: the N120 evoked potential component

Topographic differences in evoked potentials were measured in 20 off-medication chronic schizophrenics and 24 normal controls. Four intensities of brief electrical shocks were administered to the subject's right forearm in a random order at 1-second intervals. Evoked potentials (EPs) were recorded from the scalp over the left hemisphere. The EP data from 16 left hemisphere leads were used to generate EP maps of brain response for individual subjects. The maps were normalized by z transformation. Group mean maps of EP activity and unpaired t tests were then computed. Normals showed strongly localized activity in the pre- and postcentral gyri, with increasing intensity resulting in the attenuation of parietal response. Schizophrenics showed more diffuse EP activity which did not vary with intensity. Significant differences between normals and schizophrenics were found for all four intensities in posterior frontal and anterior parietal cortex. This is consistent with the findings of small EPs reported by others in the somatosensory, visual and auditory modalities.