Objective: The authors' goal was to characterize cognitive flexibility and verbal learning in relatives of patients with bipolar disorder and in euthymic patients with recurrent major depression.
Method: The intradimensional/extradimensional shift task and California Verbal Learning Test were administered to 27 first-degree relatives of probands with bipolar I disorder, 15 euthymic outpatients with recurrent unipolar depression, and 47 healthy comparison subjects.
Results: The relatives of patients with bipolar I disorder and the euthymic patients with unipolar depression were more likely to fail the intradimensional/extradimensional shift task than the healthy comparison subjects. The impairments at the extradimensional shift stage were pronounced. Verbal learning, delayed recall, and recognition were unimpaired in all groups.
Conclusions: Attentional set shifting may represent an endophenotype in mood disorder, related to underlying vulnerability rather than the actual disease phenotype.