Cognition, negative symptoms, and diagnosis: a comparison of schizophrenic, bipolar, and control samples.

Forty-six schizophrenic, 22 bipolar, and 26 normal control subjects were administered negative and positive symptoms scales and tests of cognitive function. Test performance was related to diagnosis and to positive and negative symptom ratings within the schizophrenic group. Bipolar patients were significantly superior in cognitive status when compared with all schizophrenic patients, but less so when compared only with those who did not have key negative symptoms (affective nonresponsivity and poverty of speech). The schizophrenic patients with negative symptoms displayed severe impairment, performing significantly worse than the control, bipolar, and other schizophrenic subjects. Negative symptoms thus are significantly implicated in the cognitive inferiority of schizophrenic to bipolar patients. Although the data suggest bipolar patients may also have cognitive deficiencies, these findings are inconclusive and require cross-validation.