A decade ago, Helen Mayberg first tried to treat a person with depression through deep brain stimulation (DBS) of the brain region called area 25. She and other groups, some targeting different brain regions, have subsequently used DBS to treat depression in more than 200 people. Between 40% and 60% of these patients demonstrated significant improvements, she says. The prospect that this experimental procedure can bring recovery for people who had given up hope has "reinvigorated the field" of depression treatment, says Husseini Manji, former director of the National Institute of Mental Health's Mood and Anxiety Disorders Program and head of therapeutic neuroscience at Janssen Pharmaceuticals. And it has given researchers a powerful way to pursue an old but largely untested hypothesis: that much depression results not from an imbalance in the soup of neurochemicals that bathes the brain, but from disrupted neural "circuits."