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Objective: To show that PET investigations of brain function in patients with major depression can contribute with valuable pathophysiological knowledge about brain function of these states.

Methods: PET studies of cerebral blood flow or glucose metabolism in patients with unipolar or bipolar depression were reviewed.

Results: The studies have great discrepancies related to sample size, subject selection, imaging protocol and image analysis. In spite of this shortcoming, there is evidence that patients with major depression have reduced blood flow and metabolism in the prefrontal cortex, particularly when they exhibit psychomotor retardation. Abnormalities are also found in the anterior cingulate gyrus and the basal ganglia. A few studies point to the possibility that response to antidepressant treatment can be predicted from PET scans.

Conclusion: This evidence is consistent with the hypothesis that depressive symptoms are caused by dysfunction of regions of the limbic system and the frontal lobes in close connection with the basal ganglia.