Identifying functional neuroimaging biomarkers of bipolar disorder: toward DSM-V

Bipolar disorder is one of the most debilitating and common illnesses worldwide. Individuals with bipolar disorder frequently present to clinical services when depressed but are often misdiagnosed with unipolar depression, leading to inadequate treatment and poor outcome. Increased accuracy in diagnosing bipolar disorder, especially during depression, is therefore a key long-term goal to improve the mental health of individuals with the disorder. The attainment of this goal can be facilitated by identifying biomarkers reflecting pathophysiologic processes in bipolar disorder, namely impaired emotion regulation, impaired attention, and distractibility, which persist during depression and remission and are not common to unipolar depression. In this critical review, we examine the feasibility of identifying biomarker of bipolar disorder by discussing existing findings regarding functional abnormalities in neural systems underlying emotion processing (amygdala centered), working memory, and attention (dorsolateral prefrontal cortex centered) that persist through bipolar depression and remission and are bipolar specific rather than common to unipolar depression. We then focus on future research goals relating to major clinical problems in bipolar disorder, including, the identification of biomarkers allowing detection of individuals at risk of subsequent development of the disorder. Bipolar disorder is a common, debilitating, and potentially fatal disorder. Current and future research in bipolar disorder should focus on identification of disorder biomarkers to improve diagnostic accuracy and the mental heath of those with the disorder.