Increased anterior cingulate cortex volume in bipolar I disorder

Functional neuroimaging studies have implicated the anterior cingulate cortex (ACC) in the pathophysiology of bipolar disorder (BD), but findings from volumetric studies have been less consistent, therefore the purpose of the present study was to further investigate the existence of volumetric abnormalities in the ACC cortex of individuals with BD. In addition to methodological inconsistencies many previous studies have been lacking robustness clinically with respect to characterizing bipolar patients and comparison subjects. Hence, the present study matched the groups closely across a number of demographic parameters.

Using magnetic resonance imaging, ACC volumes of 24 bipolar patients were compared to 24 gender-, age-, and education-matched control subjects, and these findings were further investigated in relation to both illness and treatment factors.

A significantly larger (26%) right ACC in bipolar patients than control subjects was seen, and this difference was not associated with a history of psychosis, familiality, or lithium treatment, after controlling for potential confounds. Patients reporting fewer affective episodes did, however, have significantly larger ACC volumes than controls, suggesting ACC volumetric changes early in the course of BD.

An increase in the size of the ACC may have important implications for the neurobiology of BD. It is suggested that attempts to control affective instability during the early stages of the illness necessitates greater ACC mediation via its role in conflict resolution and hence this is reflected in the increased size of the ACC early in the course of the illness.