Study has found that an emotion-regulating brain circuit is overactive in people who are prone to depression. The finding was reported in the August 2004 issue of Archives of General Psychiatry.
According to PsychPort.com, researchers discovered the abnormality in brains of those whose depressions relapsed when a key brain chemical messenger was experimentally reduced.
Even when in remission, most subjects with a history of mood disorder experienced a temporary recurrence of symptoms when their brains were experimentally sapped of tryptophan, the chemical precursor of serotonin, the neurotransmitter boosted by antidepressant medications.
Neither a placebo procedure in patients nor tryptophan depletion in healthy volunteers triggered the mood and brain activity changes. The scans revealed that a key motion-processing circuit was overactive only in patients in remission--whether or not they had re-experienced symptoms--and not in controls.
Since the abnormal activity did not reflect mood state, the finding suggests that tryptophan depletion unmasks an inborn trait associated with depression.
The researchers scanned subjects with positron emission tomography (PET) after their blood tryptophan levels were reduced by about three-fourths, using a radioactive tracer that reveals where the brain is active during a particular experimental condition.
Pills containing seven essential amino acids or identical-looking placebo pills were given randomly to 27 unmedicated depressed patients in remission and 19 controls.
Sixteen patients experienced a transient return of symptoms under tryptophan depletion, but their mood lifted to normal by the next day. Compared to controls, the patients showed increased brain activity in areas involved in regulating emotions.
Since brain function appears to be disregulated even when patients are in remission, they need to continue long-term treatment beyond the symptomatic phase of their illness, noted Dr. Alexander Neumeister, one of the authors of the study, conducted by the U.S. National Institute of Mental Health

Young canaries happily learn songs that sound nothing like their species, but they revert to a strict canary-like melody as they mature, Science reports.
A US team was surprised to find it could teach juvenile birds a haphazard jumble of computer generated tunes.
However, the birds’ impressive flexibility gave way to rigid rules when breeding became a priority.
Paradoxically, months of wayward early learning seems to have little impact on the birds’ ability to sing properly.
The scientists hope this puzzling course of events will help them understand how birds develop songs.
“The most surprising thing is that the birds were able to imitate, and then paradoxically they abandon this imitation in adulthood,“ said co-author Tim Gardner, of Rockefeller University, US.
“It seems an excessive capacity for imitation, which is dropped when they grow up.“

Agroup of young stars has been spotted dangerously close to the giant black hole at the centre of our galaxy--only the second such group known to be braving the region’s extreme conditions, said the New Scientist.
Two years ago, astronomers found the first cluster of young stars 0.7 light years from the black hole. How they got there is unclear, because the black hole’s gravity ought to tear apart the clouds of gas and dust from which new stars form.
The cluster may have formed farther out in the galaxy and migrated inwards, held together from within by the gravity of a middleweight black hole.
The latest group of five young stars, found by Jessica Lu of the University of California in Los Angeles and her colleagues using the Keck I telescope in Hawaii, is moving in convoy even closer to the galactic centre - just 0.26 light years away.
The stars appear to be only about 10 million years old and don’t seem to be held together by a smaller black hole. “What’s amazing is that this little group of stars can survive in this hostile environment,“ says Lu. “You would think that the stars would be quickly torn apart.“
Lu speculates that star clusters might be able to form near the supermassive black hole despite the intense gravity, radiation, pressure and heat. “The process would be very foreign to what we currently think of as star formation,“ she says. Alternatively, she adds, the stars might be remnants of a larger cluster that formed farther out and was stripped of most of its stars as it spiralled towards the black hole.