A Meta-Analytic Investigation of Neurocognitive Deficits in Bipolar Illness: Profile and Effects of Clinical State

A meta-analysis of neuropsychological studies of patients with bipolar disorder comprised of 42 studies of 1,197 patients in euthymia, 13 studies consisting of 314 patients in a manic/mixed phase of illness, and 5 studies of 96 patients in a depressed state. Cohen d values were calculated for each study as the mean difference between patient and control group score on each neuropsychological measure, expressed in pooled SD units. For euthymia, results revealed impairment across all neuropsychological domains, with d values in the moderate-to-large range (d = .5 - .8) for the vast majority of measures. There was evidence of large effect-size impairment on measures of verbal learning (d = .81), and delayed verbal and nonverbal memory (d = .80 - .92), while effect-size impairment on measures of visuospatial function was small-to-moderate (d <= .55). Patients tested during a manic/mixed or depressed phase of illness showed exaggerated impairment on measures of verbal learning, whereas patients tested during a depressed phase showed greater decrement on measures of phonemic fluency. These results suggest that bipolar illness during euthymia is characterized by generalized moderate level of neuropsychological impairment with particular marked impairment in verbal learning and memory. These results also show that a subset of these deficits moderately worsen during acute disease states.