Impaired working memory monitoring in euthymic bipolar patients

OBJECTIVES: Converging evidence suggests that patients with remitted bipolar disorder (BD) have a persistent cognitive deficit in the executive control of working memory (WM). However, the component operations that contribute to this deficit remain unclear. The aim of the present study was to further profile the nature and specificity of WM impairment in euthymic BD. METHODS: Fifty DSM-IV-confirmed patients with euthymic BD and demographically matched controls completed a modified version of the Self-Ordered Pointing Task (SOPT) and the Cambridge Neuropsychological Test Automated Battery Pattern Recognition Test along with traditional executive and WM tasks [Stroop, initial letter Verbal Fluency (FAS), Trail-Making, Digits Forwards and Backwards]. Prospective clinical ratings over one month prior to testing confirmed that patients were euthymic at test. Absence of basal hypercortisolaemia was confirmed by serial saliva sampling. RESULTS: Error analysis revealed that whilst patients made more errors on the SOPT overall, they were no more likely to perseverate than controls. Patients' erroneous responses did not proliferate across trials, suggesting that proactive interference did not contribute to their poor performance, but serial position effects were evident where patients' errors clustered towards the end of a trial. No differences were found on the recognition memory test, in WM capacity, or on two of the three traditional executive procedures (FAS and Trail-Making). However, patients' Digits Backwards was impaired. CONCLUSIONS: These data suggest that patients with BD have a deficit in their ability to monitor the contents of WM. This deficit is not an epiphenomenon of mood, but may be due to enduring brain dysfunction, integral to bipolar illness.