State dependent cortico-amygdala circuit dysfunction in bipolar disorder

- Neuroanatomical models of Bipolar Disorder suggest brain circuit pathology.
- The effect of mood state on circuit dysfunction is unclear.
- Mania is distinguished from euthymia by disruption of an amygdala-ACC circuit.
- Connectivity to structures involved in emotion regulation are disrupted in mania.

BackgroundExisting models of the pathophysiology of bipolar disorder posit disruption in neural circuits of emotion regulation and reward processing. However, few fMRI studies have compared regional brain activity and connectivity in different mood states in bipolar disorder to determine if manic symptomatology is reflected in specific circuit abnormalities. The purpose of this study was to test the hypothesis that bipolar mania is associated with altered connectivity between cortical regions thought to regulate subcortical structures such as the amygdala and striatum.Methods28 subjects with bipolar disorder in a manic state, 24 different bipolar subjects in a euthymic state, and 23 matched healthy comparison subjects underwent resting state fMRI scans. Several cortical and sub-cortical structures implicated in the pathogenesis of bipolar disorder were selected for study. We conducted a whole-brain analysis of functional connectivity of these regions.ResultsBipolar mania was differentiated from euthymia by decreased functional connectivity between the amygdala and anterior cingulate cortex (ACC). Mania was also characterized by increased connectivity between amygdala and dorsal frontal cortical structures that are normally anti-correlated in emotion regulation tasks.LimitationsBoth groups of bipolar subjects were prescribed medications. The study was not longitudinal in design.ConclusionsCompared to bipolar subjects in a euthymic state, subjects in the manic state demonstrate disrupted functional connectivity between brain regions involved in the regulation of emotion and the amygdala. This disruption of activity in neural circuits involved in emotion may underlie the emotional dysregulation inherent to a bipolar manic episode.