Can The Brain Or Head Be Transplanted?

No, a brain transplant has never been performed on a human, and none is realistic with today’s medicine. The closest experiments are animal head transplants, in which the brain stays inside its own skull. The decisive obstacle is that severed spinal nerves cannot yet be reconnected, so the transplanted brain cannot control its new body. Immune rejection is a second major barrier.

What if we could bring Albert Einstein back to life? For that matter, what if we could bring back any famous personality if their brain was well preserved? Forget bringing them back to life, but have you ever wondered whether our brains are transferrable? Imagine understanding concepts and retaining the memories of others by possessing some brilliant scientist’s brain? The idea has a Frankenstein-ish ring to it, right? But is it possible?

Humans are constantly trying to find ways to defeat disease and prolong life, but the last frontier to conquer is the human brain. People with damaged hearts, kidneys, lungs and other organs have been given a new lease of life through organ transplantation, but can the brain from one individual be transplanted into another body?

Head transplants in animals have been attempted on and off since 1908, when the French surgeon Alexis Carrel and the American physiologist Charles Guthrie grafted the head of one dog onto the neck of another. The head comprises your hair, scalp, skull, the layers of material between the skull and the brain, and finally the brain itself. A head transplant involves severing the head at the neck and stitching its blood vessels to those of a second animal, leaving you with a two-headed hybrid. The Carrel-Guthrie dog showed only flickers of reflex movement and survived just a few hours. Decades later, in 1954, the Soviet surgeon Vladimir Demikhov took the idea further, grafting the head and forelimbs of a puppy onto a larger dog. He repeated the operation more than 20 times, but the dogs rarely lived beyond a few days. In all of these early attempts, only minimal function was ever restored in the transplanted head.

In 1970, Dr. Robert White, a neurosurgeon at Case Western Reserve University, transplanted the head of a rhesus monkey onto the body of another rhesus monkey, in what he called a "cephalic exchange." Nothing like it had been done in a primate before. Because the cranial nerves stayed intact, the transplanted head could see, hear, smell, taste and even eat. But the spinal cord was never reconnected, so the animal was paralyzed from the neck down, and it died after about nine days, when its immune system rejected the foreign body.

For a while it looked as though a human version was just around the corner. In 2015, an Italian neurosurgeon, Dr. Sergio Canavero, announced a project he called HEAVEN (head anastomosis venture) and predicted that the first human head transplant, also described as Allogeneic Head and Body Reconstruction, could happen as early as 2017. A 30-year-old Russian software engineer, Valery Spiridonov, who has Werdnig-Hoffmann disease (a form of spinal muscular atrophy that progressively wastes the muscles), volunteered for the procedure. In neuromuscular disorders like his, motor function fades and gradually progresses to difficulties with breathing and swallowing, which can shorten the patient’s lifespan dramatically. The hope was that, if the operation worked, a healthy donated body from a brain-dead person could give patients with severely damaged bodies a fresh start.

It never happened. The 2017 deadline came and went with no surgery on a living person. Spiridonov eventually withdrew, having married and started a family. What Canavero and his Chinese collaborator Xiaoping Ren did announce in late 2017 was a "rehearsal" carried out on two corpses at Harbin Medical University in China, not a transplant on a living patient. To this day, no human head transplant, let alone a true brain transplant, has ever been performed, and most surgeons regard Canavero’s claims with deep skepticism.

How Is It Done?

At least on paper, here is how the proposed operation would work. The donor’s body and the recipient’s head are cooled to slow neuronal and tissue damage. The neck tissue is then dissected, the blood vessels are connected with tubes, and the spinal cord is cut with an ultra-sharp blade to keep the damage as clean as possible. The head is placed on the donor body, and after the cut ends of the spinal cord are lined up, a chemical called polyethylene glycol (PEG) is meant to coax the severed nerve fibers to re-fuse, a step Canavero named the GEMINI protocol. The blood vessels and tissues are sutured, the patient is kept comatose for several days, and the spinal cord is stimulated through electrodes to encourage the new connections. The catch is that this nerve re-fusion has only ever shown partial, short-lived results in mice and other animals, never anything close to full recovery in a person.

The Challenges

Medical professionals in the larger surgical community remain deeply skeptical that any of this could work. The biggest challenge is reconnecting the ends of severed spinal nerves, the very problem that doomed Dr. White’s monkey. Spinal nerves are the primary route by which signals travel between the brain and the rest of the body. If that connection breaks, there is no head-body link, so the brain cannot drive vital functions, and the result is death. Mammalian nerves in the central nervous system barely regenerate once cut, in part because scar tissue and inhibitory molecules block them, which is exactly why spinal cord injuries are so often permanent. Even if some axons did manage to bridge the gap, they would not necessarily reconnect to the right targets, so there is no guarantee that any useful function would return. Structure does not ensure function.

Then there is the problem faced by every organ transplant: rejection of the foreign tissue by the recipient’s immune system, even when the tissue is closely matched. To hold that off, a head-transplant patient would need to be flooded with immunosuppressants, but at the doses an entire foreign body would demand, those drugs can themselves poison the body.

Who Is Who?

Head/brain transplants also have psychological repercussions and raise some philosophical questions. If Person A’s head is attached to Person B’s body, and they stay alive, whose identity will be adopted by this fused being? Will he/she have the same memories as those of Person A? Which personality will the person adopt? If wealthy, aging individuals were to opt for such a surgery, they could in theory attain a first crude form of immortality. However, this assumes that a person is only defined by their brain, but the way that our self-image is attached to the way we think about our bodies refutes this claim. It raises fundamental psychological questions, such as what exactly is ‘self’?

For now, the medical community remains largely united in its doubts about this unique, futuristic and slightly creepy idea. Dr. Canavero was never deterred and kept insisting his technique would work, yet years after his self-imposed deadline, no living human has gone under the knife. Spinal cord fusion, the one breakthrough the whole project hinges on, still has not been demonstrated well enough even in animals to justify trying it on a person.

So, for the foreseeable future, transplanting a brain or a head remains the stuff of science fiction rather than the operating room. But if history is any guide, humanity’s hunt for ways to cheat death and disease will probably never stop!