Executive functioning and theory of mind in euthymic bipolar disorder

OBJECTIVES: To examine the nature of executive deficits in euthymic patients with bipolar disorder (BD). METHODS: Fifteen euthymic BD patients and 13 controls were administered a battery of executive tasks including verbal fluency, Stroop, Theory of Mind (ToM) tests and selected subtests from the Cambridge Neuropsychological Test Automated Battery (CANTAB). Self-report and clinician ratings of mood and social and occupational functioning were also obtained. RESULTS: There were no significant differences between BD patients and controls on the primary measures of the following executive tasks: verbal fluency, attentional set-shifting, problem solving or planning. On secondary measures of speed, BD patients were slower to complete the first trial of the Stroop task (p = 0.001). Patients with BD committed more errors across all secondary measures. Patients performed poorly when compared with controls on tests of verbal ToM (p = 0.02), and although they performed non-verbal ToM tasks at a level comparable to controls (p = 0.60), they were slower to initiate a response (p = 0.006). ToM was not significantly correlated with any measure of social and occupational functioning; however it correlated with the achievement scores of the CANTAB Stockings of Cambridge task (Pearson's r = 0.68, p < 0.01). CONCLUSIONS: Deficits found in euthymic bipolar patients suggest fronto-subcortical pathway dysfunction. This is consistent with other neuropsychological and neuroimaging research that points to a trait deficit in BD. Further investigation is necessary perhaps using more real-world tests.