DEPRESSION may be the work of a 鈥渉ard-wired鈥� circuit in the brain. Doctors
made this discovery when they applied a tiny current to a woman鈥檚 brain and
found she developed severe depression, which lifted soon after the current was
switched off.
Philippe Damier and his colleagues at the
Piti茅-Salp锚tri猫re Hospital in Paris were treating a
65-year-old woman for Parkinson鈥檚 disease. In Parkinson鈥檚, a region of the brain
that controls movement, the subthalamic region, is hyperactive. If drugs cannot
control a patient鈥檚 tremors, doctors often try applying electric currents to the
subthalamic region to treat the disease.
In this case, doctors applied a current via a tiny electrode implanted in the
subthalamic region on the left side of the woman鈥檚 brain for seven minutes. The
woman was fully conscious. While the current was switched on, she cried and
expressed feelings of despair such as 鈥淚 don鈥檛 want to live anymore鈥� and 鈥淚鈥檓
disgusted with life鈥�.
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The patient had no history of depression, and her despair disappeared less
than 90 seconds after stimulation stopped. The doctors found they could
reproduce the depression again on two different days. She did not respond in
this way when she was told the current was going on, even if it was not (The
New England Journal of Medicine, vol 340, p 1476).
鈥淭o our knowledge, this extreme emotional response has never been observed
after stimulation of a small part of the brain,鈥� says Damier. He concludes that
the current stimulates a particular neural network that brings on
depression.
Brain imaging showed that the electrode had been placed in the substantia
nigra, two millimetres below the subthalamic nucleus. Damier and his colleagues
think the current stimulated nerve fibres running through this region to brain
areas associated with unpleasant feelings, such as the amygdala.
鈥淚t is suggestive that there is specific circuitry in the brain that is
abnormal in major depression,鈥� agrees Harold Sackeim of the New York State
Psychiatric Institute in New York City. He speculates that a special circuit for
depression that discourages the severing of family ties may have evolved in the
brain.
Mark George, an expert on depression at the Medical University of South
Carolina in Charleston, adds that the finding could lead to treatments for
severe depression. 鈥淭his validates the idea that there are discrete circuits
that you can push and pull,鈥� he says. 鈥淵ou could think about designer drugs
specific for that circuit or mechanical methods. If you knew the circuit you
could begin to think about a cure that would not require lifelong medication.鈥�