Depression :: Overactive emotion-regulating brain circuit

A brain imaging study by the NIH’s National Institute of
Mental Health (NIMH) has found that an emotion-regulating
brain circuit is overactive in people prone to depression –
even when they are not depressed. 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 that is boosted by

Neither a placebo procedure in patients nor tryptophan
depletion in healthy volunteers triggered the mood and
brain activity changes. Brain 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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