Decreased activation of the anterior cingulate in bipolar patients: an fMRI study

Background: Previous neuroimaging investigations of patients with bipolar disorder have reported abnormalities of the frontal subcortical network. The role of the anterior cingulate cortex (ACC) and the dorsolateral prefrontal cortex (DLPFC) in bipolar disorder are not clear, although both regions have been shown to be components of a neural network which plays a critical role in the completion of tasks requiring self-monitoring and inhibition, functions often noted to be altered in bipolar patients. fMRI studies have helped clarify the role of specific subdivisions of the ACC and the DLPFC during the performance of cognitive challenges, including the Stroop color word test. To date, studies that have examined ACC function in bipolar patients have not differentiated subregions within this area, nor have they examined changes in these subregions in relation with DLPFC activation. Methods: To help clarify the specific roles of these regions in bipolar patients, we examined stable patients and control subjects during performance of the Stroop test using BOLD fMRI techniques. We hypothesized that bipolar patients would demonstrate reduced activation of two subdivisions of the ACC (AAA and VOA), as well as altered activation of the DLPFC, during the interference condition. Results: Results indicate that relative to controls, bipolar patients demonstrated significantly reduced signal intensity within the right AAA subdivision (p=0.011), which accompanied an increase in the DLPFC (p=0.049) during the task. Limitations: The study sample was somewhat small (11 patients, 10 controls) which limits the generalizability of the study findings, however, the patient sample consisted of well-diagnosed, stable, chronic individuals with bipolar disorder and the sample size provided enough power to detect between-group differences. Conclusions: These findings suggest differential processing strategies of bipolar patients and support the theory of altered frontal systems in these patients during the performance of cognitive tasks.