• bipolar disorder;
  • cognitive functions;
  • schizophrenia

Aims:  Earlier comparisons of cognitive impairment among patients with bipolar disorder and schizophrenia have found a largely similar profile of deficits, but results have varied between studies. This prompted the current attempt at another such comparison.

Methods:  Executive functions, memory, IQ, attention–concentration and perceptuomotor function were assessed in 48 bipolar disorder patients with operationally defined euthymia, and compared with 32 schizophrenia patients in remission, and 23 normal controls. Comparisons were re-attempted after controlling for years of schooling and residual affective symptoms.

Results:  Uncontrolled comparisons indicated that, compared to controls, both bipolar disorder and schizophrenia patients were significantly impaired on different tests of executive function, memory, IQ and perceptuomotor functions. Controlling for years of schooling and residual affective symptoms, however, served to remove most of the differences between patients and controls, apart from some aspects of executive function in schizophrenia and memory impairment in both schizophrenia and bipolar disorder. Patients with schizophrenia consistently performed worse than patients with bipolar disorder, but none of the differences between schizophrenia and bipolar disorder were significant.

Conclusions:  Patients with bipolar disorder exhibit cognitive difficulties that are very similar to schizophrenia in terms of their profile, although patients with schizophrenia may have more severe and widespread impairments. The resemblance in cognitive profiles has important implications for the etiology and treatment of both disorders.