Happiness is a Warm Electrode

In Hire's case, though, the existing technology seems to be working just fine. When I meet with her six months after the surgery, she doesn't look like a person who spent 20 years trapped in a dark mental cave. She's energetic. She shakes my hand firmly and looks me straight in the eye-something she says she simply wouldn't have been able to do before. She laughs often (and my jokes aren't even really funny). She now walks 50 miles a week, talks to her family constantly, chats with strangers at the post office. And her smile is a regular, everyday thing, not a freakish, fleeting appearance in a crowded operating room.

The stimulation has been active since a month after the surgery, when, over the course of several visits, Malone adjusted the electricity, searching for and finding the optimal pulse. Yet Hire's depression hasn't been vanquished. The disease could still be triggered by life events-a death in the family, for example-which is why Malone and the other psychiatrists stay so heavily involved in each patient's life. But now if Hire starts feeling despairing or apathetic again, Malone can adjust the stimulation enough to ward off the darkness.

I ask Diane whether it bothers her to have her mental health regulated by a machine, and she shakes her head. For the most part, she says, she forgets there's a stimulator stuffed under her chest muscles and two wires snaking up her neck, into the depths of her brain. "I wake up every morning and feel like I control how the day's going to be and don't even think about, 'Oh, gosh, I hope it's still on,' " she says. "It feels like I have the power."

Contributing editor Gregory Mone, a known fainter, remained on his feet while witnessing a DBS surgery.