Functional neuroimaging studies in mood disorders

Background: Our understanding of the neural circuitry involved in mood disorders is rapidly expanding through the ever-increasing application of functional brain imaging techniques. Objectives: A selective review of functional neuroimaging studies in patients with primary mood disorders was undertaken in order to identify points of commonality and controversy in the existing literature. Methods: Articles published between 1980 and July 2005 were identified using a range of keywords from relevant on-line databases and key journals. Results: Increased activity within limbic regions has been consistently associated with depressive states and may also be present in manic states too. Dorsal and ventral prefrontal regions appear compromised as suggested by emerging evidence of cortical inefficiency within prefrontal regions or reductions in their connectivity with limbic areas. Most of the functional changes observed are at least partly reversible following clinical remission although deficits in prefrontal regions may be state-related. Conclusions: Despite the use of disparate functional imaging modalities, there is a convergence of findings, and the results described do not appear to differ between unipolar and bipolar depression. However, further data are required in order to fully determine the functional changes occurring during manic states. Future work will also need to elucidate the effects of medication, the utility of specific cognitive tasks, and blood oxygenation level-dependent interactions within these affective states.