Introduction

Bipolar disorder (BD) is a complex neuropsychiatric disorder characterized by cognitive, emotional and motor symptoms. Multiple neuroimaging modalities have been applied to patients with bipolar disorder; nevertheless, the underlying neurobiology remains poorly understood. Data acquired with increasingly sophisticated functional neuroimaging techniques in combination with advances in neuroscience have the potential to enhance our understanding of the neuropathy of this illness. Further, these studies may provide a means of assessing those brain functional abnormalities associated with a specific phase of illness and those consistent across mood states, thus differentiating brain changes which are trait markers from those functional changes related to mood state. Moreover, functional neuroimaging is being incorporated into the development of biomarkers that may aid in clinical diagnosis and treatment selection.

The number of functional imaging studies reported in the literature has increased dramatically in recent years. Comparison of these studies is complicated by several factors. These include the fact that patient groups have been studied with significant differences in clinical variables, such as comorbidity, duration of illness and current treatment. Also, many different activation paradigms have been used for functional magnetic resonance imaging (fMRI) studies and some metabolism and blood flow studies have been conducted at rest. Nonetheless, a review of functional imaging studies may provide insights into the neurobiology of this disorder.

Since bipolar illness is a disorder characterized by dysregulation of affect as well as changes in cognitive function, it is likely that the underlying neuropathology involves the neural systems involved in the production and regulation of affect.