ABSTRACT
Developments in neuroimaging methods have brought new possibilities for in vivo studies of the human brain, allowing examination of anatomical abnormalities, brain metabolism, and in vivo brain neurochemistry with unprecedented resolution. These new methods made possible increasingly sophisticated investigations into the pathophysiological mechanisms that may be implicated in various neuropsychiatric disorders. In recent years, a growing number of brain imaging studies have started to examine the mechanisms that could be dysfunctional in unipolar and bipolar mood disorders [1-7]. The initial studies, which started early in the 1980s, consisted of computed tomography (CT) anatomical investigations, and those were subsequently followed by higher resolution magnetic resonance imaging (MRI) studies that attempted to investigate the anatomical brain abnormalities present in these disorders [3,8]. In CT and MRI anatomical studies, particular brain regions such as the prefrontal cortex, medial temporal lobe, and subcortical structures have been suggested to be abnormal. These regions participate in brain neuroanatomic circuits that may be involved in mood regulation [3,5,9-13]. In particular, two interrelated brain circuits, a limbic-thalamic-cortical circuit and a limbic-striatal-pallidal-thalamic circuit, comprise critical brain regions that may be involved in the pathophysiology of mood disorders. Abnormalities in these brain regions could result in malfunction in these interrelated circuits and could be implicated in the pathophysiology of mood disorders. Subsequent investigations examined the functional and neurochemical substrates of
abnormalities in these brain regions in mood disorder subjects. Such studies have started in recent years, are currently ongoing, and hold considerable promise to help elucidate the biological underpinnings of bipolar and unipolar mood disorders.
