To BD or not to BD: functional neuroimaging and the boundaries of bipolarity

Bipolar disorders are major mood disorders defined by the presence of discrete episodes of depression and either mania, in bipolar I disorder, or hypomania, in bipolar II disorder. There is little contention that both are serious psychiatric conditions or that they are associated with substantial suffering, disability, risk of suicide and cost to the community. Recently, focus has shifted away from classic manic-depressive illness toward a 'bipolar spectrum' model, which allows for much softer presentations to be conceptualized as bipolarity, but the boundaries of this concept remain contentious. In this article, we will consider the contribution of neuroimaging to delineating the bipolar phenotype and differentiating it from similar disorders.