Resting-state functional magnetic resonance imaging (rsfMRI) in bipolar and unipolar depression

Abstract Unipolar and bipolar depression are virtually indistinguishable at the behavioral level, yet likely show meaningful differences in underlying pathophysiology. Resting-state magnetic resonance imaging (rsfMRI) has provided a methodological window into the pathophysiology of mood disorders at the level of neurocircuitry, with greater potential for methodological standardization and generalizability than traditional task-based approaches. In this chapter, we review the existing rsfMRI literature on unipolar and bipolar depression, in an attempt to synthesize findings and probe both the overlap and divergence in neurocircuit function underlying these disorders. Existing rsfMRI studies of unipolar and bipolar depression converge upon disrupted functional connectivity within neural networks supporting self-referential (default mode network), affective and reward (salience network), and executive control (frontoparietal control network) functions. Unipolar depression is distinguished from bipolar depression by increased default mode and decreased salience network within-network functional connectivity. In contrast, bipolar depression is distinguished from unipolar depression by more diffuse disruptions in cortico-striatal-limbic-subcortical and somatosensory functional connectivity. Challenges to the interpretation of rsfMRI and implications for future intervention development are discussed.