Cognitive dysfunctions in bipolar disorder: evidence of neuropsychological disturbances

Although cognitive dysfunctions in psychosis have classically been associated with schizophrenia, there is clinical evidence that some bipolar patients show cognitive disturbances either during acute phases or in remission periods. The authors critically review the data on cognitive impairment in bipolar disorder. The main computerized databases (Medline, Psychological Abstracts, Current Contents) have been consulted crossing the terms 'cognitive deficits', 'neuropsychology', 'intellectual impairment', 'mania', 'depression' and 'bipolar disorder'. Changes in the fluency of thought and speech, learning and memory impairment, and disturbances in associational patterns and attentional processes are as fundamental to depression and mania as are changes in mood and behavior. Moreover, a significant number of bipolar patients show persistent cognitive deficits during remission from affective symptoms. However, there are several methodological pitfalls in most studies such as unclear remission criteria, diagnostic heterogeneity, small sample sizes, absence of longitudinal assessment, practice effect and poor control of the influence of pharmacological treatment. Most studies point at the presence of diffuse cognitive dysfunction during the acute phases of bipolar illness. Most of these deficits seem to remit during periods of euthymia, but some of them may persist in approximately one third of bipolar patients. Methodological limitations warrant further research in order to clear up the relationship between neuropsychological functioning and clinical, demographic and treatment variables in bipolar disorder.