Dr. Freeman, who died in 1972, presided over an estimated 3,500 lobotomies from 1936 to 1967. Early on, the actual cutting was done by his neurosurgeon partner, Dr. James W. Watts. He sawed two holes in the skull and, with a device called a leucotome, lopped off cells in the brain’s frontal lobes.

The partnership dissolved a decade later when Dr. Freeman embraced a procedure called a transorbital lobotomy. It was not for the squeamish. Dr. Freeman would insert a tool resembling an ice pick beneath each eyelid, hammer it into the patient’s brain through the eye socket, and maneuver it to cut away frontal lobe cells believed to be trouble spots.

Dr. Watts, who died in 1994, wanted no part of this. Dr. Freeman set out on his own, performing hundreds upon hundreds of what, unsurprisingly, came to be known as ice pick lobotomies. He delighted in a craft that critics deemed reckless. Part showman, he even barnstormed the country. In one 12-day period, he operated on 225 people during a swing through West Virginia.

Did he and Dr. Watts do any good? That might depend on the definition of “good.”

Dr. Watts asserted that many of their patients — men and women with severe maladies like depression, anxiety and insomnia — showed positive results in that they were able to lead productive lives postsurgery. But even more found no relief or ended up in worse shape. Ms. Kennedy, probably the team’s most famous patient, certainly qualified as an abject failure. So did Helen Mortensen, one of Dr. Freeman’s last patients. She died of a cerebral hemorrhage three days after he mistakenly severed a blood vessel.

That was in 1967. By then, lobotomies had fallen fully out of favor. Psychoactive drugs like Thorazine had come on the scene in the 1950s, followed much later by Prozac and other mood-altering pharmaceuticals. Routinely, lobotomies came to be seen as monstrous — think of Ken Kesey’s “One Flew Over the Cuckoo’s Nest” — or as ripe for joking, as in the observation by the singer Tom Waits that he would “rather have a bottle in front o’ me than a frontal lobotomy.”

Of course, drugs are not surefire successes, either, and often produce unwelcome side effects. One new frontier in neuroscience relies again on surgery, but it bears no resemblance to Freeman’s methods.

A prominent procedure is deep brain stimulation, or D.B.S.: Electrical impulses are sent to a distinct zone of the brain believed to be the root of a patient’s problem. For 20 years, this technique has had approval from the Food and Drug Administration to relieve Parkinson’s symptoms. The agency sanctioned it for treatment-resistant O.C.D. cases in 2009.

It has also been explored as a possible way to help combat soldiers with post-traumatic stress disorder. In such situations, the part of the brain known as the amygdala becomes highly activated; it is a center of emotions, including fear. The hope is that sending an electrical signal to the amygdala will calm it.

This stimulation is not to be confused with electroconvulsion, formerly known as electroshock, therapy, which involves no surgery and externally delivers a powerful one-time jolt to the brain. D.B.S. relies on implanting electrodes that produce steady flows of low-energy signals to a specific brain area deemed troublesome. The difference, in a sense, is comparable to that between a defibrillator and a pacemaker. And like pacemakers, brain stimulators are now small enough to be surgically inserted with relative comfort. More than 125,000 people worldwide are believed to be living with the implanted devices.

That does not mean the method is foolproof. As with lobotomies, not everyone is helped. Some patients report adverse effects like depression and increased suicidal tendencies. You do not need to be a brain surgeon to understand that we are talking about the body’s most complex organ. But why not take a brain surgeon’s word for it?

“We probably know about 1 percent of what the brain is doing,” said Dr. Emad Eskandar, a neurosurgeon at Harvard Medical School, who has done many implants. “The brain is incredibly complex, has 100 billion neurons, untold trillions of connections,” he told Retro Report. “So, particularly when it has to do with higher cognitive functions, like feelings and thinking and emotions, we really do not have a very good understanding of that.”

Then, too, there is the legacy of Walter Freeman and thousands of patients like Rosemary Kennedy. “There is a dark history of psychiatric neurosurgery,” and it “still overhangs our field,” said Dr. Darin Dougherty, who is in charge of neurotherapeutics at Massachusetts General Hospital. Still, Dr. Dougherty cautioned against being shackled by the past. “I really want to emphasize how far we’ve come,” he said.

CLYDE HABERMAN, a regular contributor to Retro Report, has been a reporter, columnist and editorial writer for The New York Times, where he spent nearly 13 years based in Tokyo, Rome and Jerusalem. Subscribe to our newsletter here and follow us on Twitter @RetroReport.

This article first appeared in The New York Times.