As a nurse who understood those risks, 41-year old Deanna Cole-Benjamin says she went into surgery scared. "Knowing that if this doesn't work, then what else is there," she says.
Deanna, a wife and mother of three, was so depressed, she had spent four years in mental hospitals, undergoing repeated electric shock treatments.
She estimates she had around 80 such shock treatments.
Two years ago, just before she became one of the first people to have the surgery, Deanna said, "I just feel numb, I feel empty, I feel worthless."
Today, she is one of the experiment's most striking successes.
With 15 patients treated so far, researchers claim 10 have responded positively. And most of them were, like Deanna, depression-free within six months of surgery, with no apparent side effects.
When Debra heard about the experiment, she begged to be part of it. 60 Minutes spoke to her a few days before her operation last March.
"You don't feel, to me, like you're really afraid," Stahl remarks.
"I'm afraid of it not working. I'm very afraid of it not working," Debra says.
60 Minutes joined her in the O.R. the morning of her surgery. A metal frame is placed on her head to keep her immobile.
Debra will be awake and un-sedated during the operation. Once the stimulator is turned on, she can tell Doctors Lozano and Mayberg if she notices any lifting of her mood.
As they start drilling holes in Debra's skull, the reality of it all hits her.
"That's okay. That's okay. Just hold my hand," Dr. Mayberg said to Debra.
"I can't believe this is happening," Debra said. "It's just been such a long struggle."
Yet, while lying on the table, Debra acknowledged she was not really optimistic.
Dr. Lozano slides in the first of two electrodes. A loudspeaker in the operating room erupts with pops and pings.
It's the sound of nerve cells "talking" as the wire hits them. Believe it or not, nerve cells in Area 25 have a distinctive chatter that helps doctors know the electrode is in the right place.
As he turns on the electric current, Dr. Lozano hopes Debra will feel the flash that Deanna did, the moment her depression lifted.
"I was distinctly hit with being overwhelmed with color in the operating room," Deanna recalls. Before, she says she had been seeing everything in black and white and gray.
"But I didn't know it until it was given back to me," she says.
With Debra, Dr. Lozano tries several settings on the left side of her brain, searching for the sweet spot.
But Debra felt no change in her mood and began to lose hope. She got a pep talk from Dr. Mayberg.
"Do the best you can. 'Cause you're getting yourself psyched out," she told Debra.
They switch over to stimulating the right side of Debra's brain and suddenly she perked up. Things seemed brighter in the operating room, and more colorful.