Head Transplants

by Brian Dunning
June 15, 2021

Today we're going to explore one of the last great frontiers of medicine: the idea of transplanting one person's head onto another person's body. It's a concept that has one foot in the world of science fiction and the other in macabre horror; or that has one foot in medical reality and the other in Barnum-style hoaxes. We've all heard something or other about head transplants, that it might have been tried on animals, or in Nazi concentration camp experiments, or even in modern medicine. Maybe you've even heard that doctors in China or someplace have already performed them. Today we're going to find out what's true and what's not about head transplants.

I'm going to start by stating right out that this podcast will not address the ethical implications of such procedures. Since the earliest days of the very first life-saving organ transplants, doctors and scientists have been charged with "playing God" and offended the principles of all kinds of people. These are questions for the ethicists and the philosophers. My job today is to discuss the state of the science behind doing head transplants, and the true facts of what has and has not actually been done so far. So please, save your questions and feedback about the ethics involved, and give them instead to the ethics and philosophy podcasts.

I'll lay one more ground rule, and that's that I'm going to break with convention and call this what it really is: a body transplant, not so much a head transplant. The patient would not be getting a new head, because that wouldn't still be the same patient; they'd be getting a new body. The common term is head transplant, so that's what I used in the episode title so people would understand what it's about. But for consistency and logic in our discussion, we're going to refer to transplanting the body.

First, we should note that there genuinely is a place for this in medical reality. A donor body could give someone without body function a chance at a renewed life, though one with severe limitations. The recipient would almost certainly be permanently paralyzed, and it's not clear how much autonomic function (heartbeat, respiration, digestion, etc.) might need to be permanently mechanically supported; but for some people, even that would be a huge improvement. Thus, there is no shortage of patients who would be glad to volunteer. The typical body transplant candidate is someone who is already paralyzed and thus has little to lose, but whose body is failing and who doesn't have much time left to live, or who lives in acute distress. Donor bodies are also (unfortunately) not very scarce, as there seems to be a constant supply of trauma victims who end up brain dead with bodies that are otherwise healthy. Today they end up donating multiple organs, eyes, skin, hands, and even faces. This would be just one more type of donation that results in a death that, while tragic, at least confers additional life onto a thankful recipient. The medical need thus established, doctors and neuroscientists have been thinking about body transplants for a long time.

Actual work began at the start of the 20th century, when French doctor Alexis Carrel developed the first successful surgical techniques for reconnecting severed vessels. Previously, such attempts caused hemorrhages and embolisms. Carrel worked with American physiologist Dr. Charles Guthrie to research limb and organ transplantation. Their most notable experiment was to take the head from one dog and connect it to another living host dog's neck, running the blood from the host dog's heart to the decapitated dog's head and then to the host dog's head. But no complete connection was made, and the dogs were euthanized after a few hours, as planned. Carrel and Guthrie received the Nobel Prize in Physiology and Medicine in 1912 for this work.

Some forty years later, Soviet surgeon Dr. Vladimir Demikhov took this to the next level. He took the front half of a small dog — everything from the shoulders up — and grafted it to the back of a host dog's neck, creating the infamous "two-headed dogs" that can easily be found on the Internet. It almost looks like the smaller dog is riding piggy back on the host dog, with its forelimbs (still attached) clinging to the host dog's neck. In this case, the connection was much more complete, and one such pair of dogs lived 29 days; most other pairs that he created lived only a few days. The dogs appeared to retain their doggie faculties; the small dog would even drink from a bowl — even though its esophagus went nowhere, and it could not bark as it had no lungs. The eventual cause of death was tissue rejection. It was the 1950s, and immunosuppression drugs did not yet exist; rendering all such experiments doomed to failure. They were quite literally ahead of their time, and Demikhov, Carrel, and Guthrie all knew that what they were doing would not be possible to try in humans.

But this was not the case for the next doctor to make milestone efforts in the field of body transplantation. American neurosurgeon Dr. Robert White took a slightly different experimental strategy in 1965. He took the brain of a dog — just the brain — and implanted it within the chest cavity of a host dog. It had a full blood supply, and White connected electroencephalogram (EEG) leads to the implanted brain. White repeated this six times, and in all six, EEG activity of the implanted brain was comparable to that of the host dog's brain. Of course no one can say whether those implanted brains remained conscious, but they certainly remained alive and active. However, the longest any host dog survived was two days.

Then in 1970, White attempted the first true full body transplants. He used four pairs of rhesus monkeys, the heads connected to each donor body by the carotid artery and jugular vein. As the monkeys would be completely paralyzed anyway, White kept it simple and did not connect the neck muscles or attempt the hopeless task of repairing the spinal cord. Nevertheless, the monkeys maintained normal EEG patterns, and were able to bite and chew, and track subjects with their eyes. But the blood supplies to the heads was never good, and the longest survival was only 36 hours. As you can imagine, White was the target of immense protest and ethical complaint, but as stated, we're not getting into that aspect today.

As late as the 1990s, White was still continuing his experiments, perfecting his techniques using recently deceased humans. He died in 2010.

Then, beginning in 2013, the most successful procedures to date were performed in China, by Dr. Xiaoping Ren, using mice. Ren had been part of the team that performed the first successful hand transplant in 1999. Similar to Demikhov's dog experiments, Ren grafted mouse heads onto host mouse's necks, but this time using the latest microsurgical techniques, and this time leaving the host mouse's cardiovascular system intact. Many pairs did not survive, but of those that did, the longest survival was a full six months. Blood pressure was successfully maintained, and the behavior of surviving mouse pairs appeared normal. Ren and his team in China also performed many complete body transplants on mice, though none ever lived for more than a day.

Today, the most visible scientist continuing the work of body transplants is the Italian neurosurgeon Dr. Sergio Canavero, who has spoken of his long collaboration with Ren. The collaboration has been somewhat one-sided: Canavero pushes Ren to use his lab and relaxed oversight for human experiments, while Ren reminds him that good results in mice do not translate to humans. Canavero — also the author of a book on seducing women — is something of a controversial character. To hear him speak — he's given two TEDx talks that have inspired cult-like legions of gullible, non-expert fans — you'd think he's discovered the fountain of youth that can be immediately and miraculously given to anyone with but a few flicks of the scalpel. Both of his TEDx talks (one of which literally opened with the inauspicious line "All the experts know is wrong") have been flagged by TED as "speculative and questionable", but not removed from the TED library as they do with the worst offenders. Unsurprisingly, Canavero has drawn tremendous amounts of ire and vituperation from ethicists and other neuroscientists. But at the same time, his work in the field is legitimate, science-based, and voluminous. He's built on the work of his many predecessors, methodically and logically taking everything to the next step. Judging by his work, he is certainly not a crackpot; but judging by his words, he takes a few steps too far into that territory. If he says something, be skeptical; but when he does something, it's probably a safe bet that it was done within the scope of established science. So, as I said, a controversial (and complex) character.

Canavero repeated White's monkey body transplantation in 2016, and in 2017 announced that he had successfully performed a human body transplant. However, he neglected to mention that it had been performed with cadavers — also just as White had already done. As of this writing, Canavero asserts that the needed science is now all in place, and calls for actual human body transplants to begin. After all, there are patients who want them, and whose quality of life is low enough that they are willing to risk being the guinea pigs.

Most everyone else in the field disagrees. Ren and Canavero both place their faith in PEG, polyethylene glycol, regarded by some as a sort of nerve glue. Flood the two severed ends of spinal cord with PEG, so the idea goes, and nerve membranes will be preserved long enough to heal together. It works fine on mice, but mice already have an ability to regrow nerve tissue that humans don't have — which is why Ren used them for his experiments. Neurosurgeons who aren't Canavero see little such potential when it comes to human spinal cords. Without a spinal cord, transplanted bodies would have to live their entire lives on full mechanical life support. There are potential solutions, or at least partial solutions, on the distant horizon though: stem cell treatments for improving spinal cord regeneration, and also neural implants to regain limited function by bypassing the cut.

So to summarize, the short answer for now is no, full body transplants are not coming any time soon, at least not without profound limitations, and certainly not with the support of ethicists. That particular objection is an extreme one. It is certainly possible that it's been tried; I wouldn't be at all surprised to learn that some doctor, perhaps even one associated with those we've talked about here, had actually tried it someplace confidentially, with a patient giving full consent; but any such attempts that might have been made were probably unsuccessful, given that no such thing has ever been revealed. It might happen tomorrow or next year, but the biggest challenge of reconnecting spinal cords is one that still eludes our science. So, next time you hear that a body transplant has been successfully performed on humans, or that it's surely right around the corner, I encourage you, as always, to be skeptical.

Special thanks to Dr. Brandy Schillace, author of Mr. Humble and Dr. Butcher about the history of head transplantation, and who provided her book and additional information.

By Brian Dunning
Follow @BrianDunning