Better known as "lobotomy" (a new label conjured up by American psychiatrists), the revolutionary technique seemed to be the first way psychiatrists could dramatically alleviate madness and suffering in people thought to be incurably deranged, violent, and psychotic. Extreme but—in its way—effective, the technique involved slicing tiny slivers through the frontal lobes of the brain, which surgeons reached through holes bored in the top of the skull.

It was decreed "the worst idea on the mind" in history in a public debate at the Royal Institution in 2006. Yet it seemed like such a good idea at the time—so good, it won its devisor the Nobel Prize. Portuguese neurosurgeon Dr Egas Moniz —whose gout-scoured face one graced the 10,000 Escudo banknote—won the most prestigious award in science in 1949 for developing the "leucotomy".

"Most people don't know about this chapter in our history because it's ugly, and truthfully, psychiatrists have an interest in hoping that people don't know too much about it," said Jack El-Hai, author of The Lobotomist , a biography of Walter Freeman, who performed 3,500 lobotomies and spurned other medics across the globe to embrace the procedure.

The truth, as always, is more complex. Lobotomy was widely thought of (if only for a few years) as truly revolutionary. In a 1937 story, New York Times reporter William Laurence lauded it as a "surgery for the soul". Some 40,000 Americans underwent the procedure, peaking at 5,000 annually in 1949. So popular, hundreds of people volunteered to have surgical tools inserted into their brains twice—and a handful, three times.

Today, the word "lobotomy" is synonymous with "butchery"—a form of neurological oppression used to sedate and immobilize the sick and troublesome. An extreme form of punishment, made famous by the surgical fate of Randle P McMurphy in One Flew Over The Cuckoo's Nest.

Grim it may sound, but before antipsychotics, sedatives, and all the other ingredients in our pharmaceutical repertoire, psychiatrists had few options to treat any form of severe mental illness. Moniz theorized that obsessive, depressive, and delusional behaviours were caused by excessively tight associations between neural circuits, which could be alleviated by slicing through the deep white matter of the frontal cortex, "soft as warm butter".

Freeman outlined the "prefrontal lobotomy" in full detail in a 1942 paper in the Bulletin of the New York Academy of Medicine. The Nobel Prize winner's biggest fan, Freeman sought to rebrand and reinvent the surgery by coming up with a way to enter the brain from below, rather than drilling in through the top. Why bother with an expensive, intrusive and dangerous hospital procedure, requiring heavy anesthetics and a long hospital recovery, when a different tactic could achieve the same result in less than ten minutes?

One of these children was Howard Dully, whose stepmother paid Freeman $200 to lobotomize the 12-year-old boy in 1960 for his strange behaviour, which spanned from daydreaming to a reluctance to go to bed.

Freeman became increasingly evangelical about his procedure, travelling across America to perform up to 25 treatments in a day at the nation's overcrowded mental institutions (often ungloved). He transitioned from thinking of the therapy as a last resort to advertising it as an early intervention, enthusiastically doling it out for post-partum depression, sadness in the terminally ill, and even 19 children under the age of 18, including one four year old.

In Freeman's mind , the root of a broad spectrum of mental ailments—from depression to schizophrenia and the symptoms we would today categorize as autism—lay in the same culprit: an excessive number of connections between the thalamus (an integral component of the brain's emotional hubs), and the frontal cortex (thought of as the seat of consciousness and self-awareness). Animalistic, emotional urges overwhelmed reason and rationality. Slicing through those excessive connections with an ice pick with the same motion as beating an egg could relieve the oppression of emotion over reason, alleviating anxiety and misery.

Freeman took pride in the fact many patients could walk out of his office within hours of a treatment (albeit with bruised eyes). In the end, roughly a third of the lobotomies performed in the US were achieved through the eye socket, not the skull.

Hoping for a safer, gentler option, Freeman came up with a radical alternative: driving a surgical tool into the brain by hammering it through the bony case of the eye just above the eyeball, just under the eyelid. His instrument of choice: an ice pick, plucked from the family's kitchen drawers . Instead of general or local anesthetic, Freeman opted to immobilize his patients with electroshock therapy.

Dully went on to write a memoir of his experience, My Lobotomy, found a charity to eliminate child abuse, and track down a handful of Freeman's other patients for National Public Radio in the US.

"I've always felt different—wondered if something was missing from my soul," Dully, who has no memory of the surgery, told NPR.

"I went into the project thinking he was probably a monster, but what changed my mind was seeing all the correspondences he had with his patients," says Freeman's biographer El-Hai. "He stored boxes and boxes of letters from them and their families, thanking him for his help, inviting him over for dinner. Some of his patients and their families really thought of him as family. It seemed something much deeper was going on."

On one infamous occasion at the Langley Porter Psychiatric Institute in San Francisco, he poured out a box of more than 500 cards his lobotomy patients had sent him.

Freeman spent much of the last 20 years of his life travelling across America in an old green Ford, visiting former patients and documenting their histories—progress, deteriorations, deaths and all.