Brain circuit is linked to depression

People with depression appear to have an overactive brain circuit that can stay turned on even when they are not feeling down.

Scientists at the National Institute of Mental Health deliberately induced some symptoms of depression in patients by giving them a cocktail of amino acids, said Dr. Alexander Neumeister, a researcher now at Yale University in Connecticut. The correct mix lowers levels of the amino acid tryptophan. The body converts tryptophan into serotonin, the neurotransmitter -- message-carrying chemical -- that is boosted by many antidepressants.

They tested 27 people who had been treated for depression but who were feeling healthy and taking no medication at the time of the test, and compared them to 19 people who had never suffered from depression.

About 60% of the former depression patients had their symptoms come back temporarily when their tryptophan was depleted, Neumeister said. PET scans showed abnormal activity in certain regions known to be associated with depression in the front and center of the brain.

The same thing happened in the 40% of depression patients who did not feel any symptoms.

And, writing in the Archives of General Psychiatry, Neumeister and colleagues said that none of the 19 non-depressed participants showed this same pattern of brain activity. “This shows something is really wrong in this particular circuit,” Neumeister said. “It is another argument that people should stay on their medications.”