Differences in resting corticolimbic functional connectivity in bipolar I euthymia.

Objective:   We examined resting state functional connectivity in the brain between key emotion regulation regions in bipolar I disorder to delineate differences in coupling from healthy subjects.

Methods:   Euthymic subjects with bipolar I disorder (n = 20) and matched healthy subjects (n = 20) participated in a resting state functional magnetic resonance imaging scan. Low-frequency fluctuations in blood oxygen level-dependent (BOLD) signal were correlated in the six connections between four anatomically defined nodes: left and right amygdala and left and right ventrolateral prefrontal cortex (vlPFC). Seed-to-voxel connectivity results were probed for commonly coupled regions. Following this, an identified region was included in a mediation analysis to determine the potential of mediation.

Results:   The bipolar I disorder group exhibited significant hyperconnectivity between right amygdala and right vlPFC relative to healthy subjects. The connectivity between these regions in the bipolar I disorder group was partially mediated by activity in the anterior cingulate cortex (ACC).

Conclusions:   Greater coupling between right amygdala and right vlPFC and their partial mediation by the ACC were found in bipolar I disorder subjects in remission and in the absence of a psychological task. These findings have implications for a trait-related and clinically important imaging biomarker.