Alterations in Cerebral Laterality During Acute Psychotic Illness

• A dichotic listening test was used to assess cerebral laterality in 26 right-handed patients with schizophrenic, schizoaffective, or primary major depressive illness and in 23 controls. Clinical state was assessed by twice-daily nurses' ratings and patient self-ratings. Ratings of psychotic thought and behavior were lower during the week of highest laterality than during the week of lowest laterality (P <.01). Similarly, when most improved, patients had higher laterality than when most ill (P <.01). Changes in laterality were not specific to diagnostic group, were not present in control subjects, could not be related to direct drug effects, and were independent of changes in accuracy of performance. There were large, stable, interindividual differences in degree of lateralization, but no differences between patients and controls. These results are consistent with the hypothesis that in acute psychotic illness there is a breakdown in the interhemisphere inhibition that normally mediates cerebral laterality.