Cerebral laterality, symptoms, and diagnosis in psychotic patients.

A dichotic nonsense test and a dichotic word test were used to assess cerebral laterality in 100 acutely symptomatic inpatients. Schizophrenic patients had significantly lower right ear advantages (REAs) than healthy controls, depressed patients, or schizoaffective patients. Manic patients did not differ from any other group, but manics with lower REAs were likely to have more symptoms of thought disorder than of mood disturbance while the reverse was likely to be true for manic patients with higher REAs. A subset of patients tested after symptom remission showed recovery-related increases in REA on the nonsense test and decreases on the word test, replicating previous findings. Those schizophrenics with evidence of greater disease-related decreases in REA on the nonsense than on the word test had predominantly negative symptoms whereas those with similar changes on the two tests had predominantly positive symptoms. These observations suggest the hypothesis that positive symptoms are related to overactivation of a dysfunctional left hemisphere by right hemisphere input while negative symptoms reflect a left hemisphere deficit state.