Depression Traced to Overactive Brain Circuit

A NIMH brain imaging study has found that an emotion-regulating brain circuit is overactive in people prone to depression — even when they are not depressed. Drs. Alexander Neumeister, and colleagues 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 that is boosted by antidepressants. Neither a placebo procedure in patients nor tryptophan depletion in healthy volunteers triggered the mood and brain activity changes. NIMH positron emission tomography (PET) scans revealed that a key emotion-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.

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