Neurobiology of Bipolar Disorder

As frequently occurs in science, progress made on the neurobiology of bipolar disorder has followed a nonlinear course that often revisits deserted concepts. The neurobiological blueprint of bipolar disorder continues to unfold from a neurotransmitter-based hypothesis to include peptides and intracellular signaling pathways, and into a broader neuronal network perspective that involves cortical and subcortical regions in the brain. Moreover, new evidence makes it increasingly clear that the mechanisms of disease in bipolar disorder extend beyond the brain, providing plausible “missing links” between psychopathology and the elevated medical comorbidities. This is illustrated by the expanding role of the circadian system in bipolar disorder and the emerging evidence on the contribution of spinal afferents to the construct of mood, portraying that brain–body communication pathways are relevant to the pathophysiology of bipolar disorder. This chapter provides an overview of the current and emerging neurobiological frameworks for bipolar disorder.