BETHESDA, Md -- August 4, 2008 -- Using brain imaging, researchers have produced direct evidence that people prone to depression have abnormal mood-regulating brain circuitry, making them vulnerable to relapse when levels of certain key brain chemical messengers plummet. The study appears in the May issue of Archives of General Psychiatry.
Wayne Drevets, MD, Mood and Anxiety Disorders Program, National Institutes of Mental Health, Bethesda, Maryland, and colleagues, studied 15 unmedicated patients in remission who had a history of depression by giving them a drug that temporarily depleted their brains of dopamine and norepinephrine.
These subjects experienced an increase in depression symptoms and a decrease in the ability to feel pleasure. Positron emission tomography (PET) scans showed that this was accompanied by an increase in activity in a depression-implicated brain circuit.
By contrast, activity decreased or remained unchanged in the same brain circuit with depletion in 13 healthy participants who experienced only minor mood effects. Activity in specific brain structures in the circuit corresponded with a set of mood effects.
Dopamine normally functions in the circuit to inhibit runaway activity of emotion hubs deep in the brain by higher brain centres. Depleting dopamine effectively takes the brakes off the emotional hubs in depression-prone individuals -- hence the increased circuit activity, the researchers suggest.
"The subjects in remission from depression experienced symptoms qualitatively similar to those they had during major depressive episodes," said Dr. Drevets. "Our findings suggest that depression is associated with persistent vulnerability for developing such responses to reduced dopamine and norepinephrine neurotransmission."
PET graphics from this study can be seen here: http://www.nimh.nih.gov/science-news/2008/depression-patients-brain-circuitry-makes-them-vulnerable-to-relapse.shtml
SOURCE: National Institutes for Mental Health
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