Executive function impairments are a core feature of bipolar I disorder (BD-I), not only present during acute episodes but also persisting following remission of mood symptoms. Despite advances in knowledge regarding the neural basis of executive functions in healthy subjects, research into morphological abnormalities underlying the deficits in BD-I is lacking.Methods
Patients with BD-I within three months of sustained remission from their first manic episode (n = 41) underwent neuropsychological testing and a 3T magnetic resonance imaging scan and were compared to healthy subjects matched for age, sex, and premorbid IQ (n = 30). Group dorsolateral prefrontal cortex (DLPFC; Brodmann areas 9 and 46) and caudate volumes were examined and analyzed for relationships with the average score from three computerized tests of executive function: Spatial Working Memory, Stockings of Cambridge, and Intradimensional/Extradimensional Shift.Results
Right caudate volumes were enlarged in patients (z=3.57, p < 0.05 corrected). No differences in DLPFC volumes were found. Patients showed large deficits in executive function relative to healthy subjects (d=−0.92, p < 0.001). While in healthy subjects, a larger right (r = +0.39, p < 0.05) and left (r = +0.44, p < 0.05) caudate was associated with better executive function score, in patients, larger right (r=−0.36, p < 0.05) and left (r=−0.34, p < 0.05) volumes correlated with poorer performance.Conclusions
Although the etiology of gray matter changes is unknown, volume increases in the right caudate may be an important factor underlying executive function impairments during remission in patients with BD-I.