The Effect of Recurrent Depressive Episodes on Cognitive Impairment in Bipolar Disorder

Abstract

Cognitive impairment has been observed in both the stable euthymic mood state as well as in the acute manic and depressive mood states of bipolar disorder, making it both a trait-like and statelike aspect of the illness. However, there is a lack of longitudinal research regarding the catalytic effect recurrent acute mood states have on cognitive impairment. We conducted a longitudinal analysis of cognition on data collected from the Heinz C. Prechter Study of Bipolar at the University of Michigan. We analyzed both trait-like deficits of bipolar patients (n = 254) when compared to healthy controls (n = 93) as well as state-like deficits of repeatedly depressed affective bipolar patients (n = 68) when compared to both repeatedly non-affective bipolar patients (n = 55) and healthy controls (n = 79). We hypothesized that cognitive scores would be markedly decreased in the bipolar cohort when compared to healthy controls, and that the presence of repeated depressive mood symptoms would further down regulate cognition. We found deficits in the bipolar cohort when compared to healthy controls in the cognitive domains of visual memory, verbal fluency, influence resolution, and inhibitory control. However, we observed more marked state-like deficits in verbal fluency and visual memory in the bipolar depressed cohort when compared to both the bipolar non-depressed and healthy cohorts. Our research calls into question the notion of trait-like cognitive impairment in bipolar disorder, as repeatedly non-depressed subjects demonstrated cognitive profiles more similar to the healthy controls. Meanwhile, recurrent depressive episodes demonstrate a significant burden to cognition in bipolar patients.