Evidence of right cerebral hemisphere dysfunction in schizophrenic patients with left hemisphere overactivation.

A number of laterality studies have used initial lateral eye movements as a measure of unbalanced frontal hemisphere activity. Several of these studies have demonstrated that schizophrenics look to their right more often than normals or depressives when thinking about spatial and/or emotional material. This increase in right gaze responses has been taken to represent increased left hemisphere responsiveness for spatial and emotional material. Thus, it was predicted that schizophrenics would be more receptive to spatial material and would detect rapidly appearing spatial stimuli presented to their left hemisphere more accurately than in their right hemisphere. Further, it was expected that schizophrenics would perform better than controls when identifying rapidly presented shapes in the left hemisphere. Using visual half-field presentation of verbal and spatial material, the experimental prediction of increased left hemisphere accuracy for shape detection within the schizophrenic group was corroborated. However, there was an unanticipated and significant right hemisphere deficit for spatial identification between the schizophrenic group and the normal controls. This finding suggests that schizophrenics may have a primary deficit in their right hemisphere, which affects visuospatial processing. It is suggested that the apparent left hemisphere increase in activity for spatial material reported by Gur and Schweitzer may thus be a compensatory mechanism for a primary failure of the schizophrenic's right hemisphere to maintain normal attention and vigilance.