Brain Imaging Studies Shed Light on Anhedonia in Depression

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Interview with Dr. Drevets

May 12, 2008 (Washington, DC) — Imaging studies of patients with depression have identified brain-circuit abnormalities that correlated with symptoms of anhedonia and have shed light on the plasticity of brain circuits in depression, Wayne C. Drevets, MD, from the National Institute of Mental Health (NIMH), in Bethesda, Maryland, said in a press conference at the American Psychiatric Association 61st Annual Meeting.

"People with depression have an inability to experience usually rewarding stimuli as being pleasurable, and so they often lose incentive and motivation, and we . . . show some imaging data that begin to account for the mechanisms that explain [this lack of pleasure, or anhedonia]," he noted.

This research is a first step in the development of more targeted treatments for depression, but in the meantime "many of the drugs that we already have available . . . as antidepressants or mood stabilizers are being shown to have important neuroplastic effects by way of enhancing neurotropic factors and neuroprotective factors in the brain," he told Medscape Psychiatry.

In a review of 5 neuroimaging studies done in about 120 depressed patients and a similar number of healthy patients while they performed reward processing tasks, Dr. Drevets and colleagues found that the depressed patients had abnormalities in their "reward-learning pathway" (Drevets WC, Furey ML. Emotional disorders: depression and the brain. In: Squire L et al, eds. The New Encyclopedia of Neuroscience. 4th ed. New York, NY: Elsevier Publishing, in press.) The studies, using functional magnetic resonance imaging (fMRI) and positive emission tomography (PET), showed that the depressed patients had abnormal patterns of neural activity in brain circuits that involve dopamine in the ventral striatal region, which has been implicated in the brain's reward pathway.

Study participants performed a "monetary incentive delay task," in which they had the ability to win money.

"In the end, healthy and depressed people won the same amounts of money, but people in the depressed group still felt bad," Dr. Drevets said in a press release issued by the NIMH. "They felt and did worse, in fact, when informed how they were doing. By contrast, such information had no effect on the mood or performance of healthy subjects. In addition, as the subjects received rewards, dopamine was released in the brains of healthy individuals, but not in depressed individuals."

Brain scans revealed that when the depressed patients knew their performance was being tracked and they had the opportunity to win money, they did worse on the tasks and had an increase in activity in the amygdala, a brain region associated with emotions such as fear.

The brains of the depressed patients "seem to pass over the potential pleasure of winning money to focus on unpleasant emotions caused by the potential for failure," said Dr. Drevets.

Too Early for Use as a Diagnostic Tool

"Unfortunately, the imaging findings typically don’t show the sensitivity and specificity that one would need to use them as a diagnostic tool," Dr. Drevets cautioned. For example, a blood sugar of 400 mg/dL is clearly outside the normal range, he added, whereas since imaging studies of depression and bipolar disorder are still in their infancy, there are no well-established normal vs abnormal imaging findings for these disorders.

Dr. Drevets has indicated that he has no significant financial relationships to disclose.

American Psychiatric Association 161st Annual Meeting: Symposium 35. May 3-8, 2008.

Medscape Medical News © 2008  Medscape

Cite this: Marlene Busko. Brain Imaging Studies Shed Light on Anhedonia in Depression - Medscape - May 12, 2008.