A quick glance at your calendar will reveal that we're now in 2017. 2017, you may recall, is the year when contraversial surgeon Sergio Canavero has promised to perform the world's first human head transplant.

But just how feasible is a human head transplant? Is it the stuff of science fiction, or does it have a basis in current sceintific thinking? Read on for everything you need to know about 2017 most alarming scientific development.

A human head transplant is exactly what it sounds like taking one living head and putting it onto a new body.

But actually, thats a little misleading. In real terms, its a body transplant, as the head will be gaining a new body to control. However, as the term whole body transplant is already used to mean transferring the brain between bodies, calling it a head transplant makes it clear that the whole head is to be switched, brain included.

Until recently, a head transplant seemed totally implausible, but the Italian scientist Dr Sergio Canavero believes its possible, and intends to conduct the first surgery in 2017.

Canavero outlines the procedure in detail here, but these are the basics of the process. Remember: dont try this at home, kids.

The donor body and the head to be attached are first cooled down to 12-15C to ensure that the cells last longer than a few minutes without oxygen. The tissue around the neck is then cut, with the major blood vessels linked with tiny tubes. The spinal cord on each party is then severed cleanly with an extremely sharp blade.

"Post coma, Canavero believes the patient would immediately be able to move, feel their face and even speak with the same voice."

At this point, the head is ready to be moved, and the two ends of the spinal cord are fused using a chemical called polyethylene glycol, encouraging the cells to mesh. This chemical has been shown to prompt the growth of spinal cord nerves in animals, although Canavero suggests that introducing stem cells or olfactory ensheathing cells into the spinal cord could also be tried.

After the muscles and blood supply are successfully connected, the patient is kept in a coma for a month to limit movement of the newly fused neck, while electrodes stimulate the spinal cord to strengthen its new connections.

Following the coma, Canavero anticipates that the patient would immediately be able to move, feel their face and even speak with the same voice. He believes physiotherapy would allow the patient to walk within a year.

He explains his suggested methods in the TED talk below.

Sceptical would be a nice way of putting it. Horrified would, in most cases, be more accurate.

Dr Hunt Batjer has attracted headlines for being particularly blunt: I would not wish this on anyone. I would not allow anyone to do it to me as there are a lot of things worse than death.

Dr Jerry Silver witnessed the 1970s monkey head transplant experiment more on which later and describes the procedure as bad science, adding that just to do the experiments is unethical. This is a particular blow to Canavero, as he states that Silvers own work in reconnecting rats spinal cords should give hope to the human head transplant. Silver dismisses this: To sever a head and even contemplate the possibility of gluing axons back properly across the lesion to their neighbours is pure and utter fantasy in my opinion.

Dr Chad Gordon, professor of plastic and reconstructive surgery and neurological surgery at Johns Hopkins University, agrees that Canaveros claims are scientifically implausible. He told BuzzFeed: Theres no way hes going to hook up somebodys brain to someones spinal cord and have them be functional.

On the conservative side, were about 100 years away from being able to figure this out, he continued. If hes saying two, and hes promising a living, breathing, talking, moving human being? Hes lying.

Dr Paul Myers, associate professor of biology at the University of Minnesota at Morris, puts it even more explicitly: This procedure will not work... Try it with monkeys first. But he cant: the result would be, at best, a shambling horror, an animal driven mad with pain and terror, crippled and whimpering, and a poor advertisement for his experiment. And most likely what hed have is a collection of corpses that suffered briefly before expiring.

Others wonder whether Canavero might simply be enjoying the limelight with a PR stunt, including Dr Arthur Caplan, director of ethics at the NYU Langone Medical Centre. Describing the doctor as nuts, he explained to CNN: Their bodies would end up being overwhelmed with different pathways and chemistry than theyre used to, and theyd go crazy.

"We'll probably see a head on a robot before we see it on [another] body," he told Live Science.

Dr John Adler of Stanford University's school of medicine is slightly more optimistic... but not much more. "Conceptually, much of this could work, but the most favourable outcome will be little more than a Christopher Reeve level of function," he told Newsweek.

Canavero is aware of this criticism, claiming that silently hes received a lot of support from the medical community. Of Dr Batjers comments that the surgery would be a fate worse than death, Canavero is scathing. Hes a vascular surgeon. A vascular surgeon of the brain, yes, but he knows nothing, he argued. How can you say such a thing? Its incredible.

"The world is moving, the critics are dwindling. Of course, there will always be critics. Science teaches us that when you propose something groundbreaking, you must be confronted by criticism. If no critics really step forward, you are saying nothing special," he told Medical News Today.

Dr Canavero also believes that the operation could essentially be used to revive the dead, if brains were suitably frozen and stored. In an interview with German magazine Ooom, Canavero said: "We will try to bring the first of the company's patients back to life, not in 100 years. As soon as the first human head transplant has taken place, i.e. no later than 2018, we will be able to attempt to reawaken the first frozen head.We are currently planning the world's first brain transplant, and I consider it realistic that we will be ready in three years at the latest."

No-one has ever attempted a human head transplant before, and attempts on animals have to put it charitably had limited success.

Image: from Motherboard, uploaded under fair use from a 1959 issue of Life

The photo above really does show a dog with two heads and its not a fake. This was the work of Soviet scientist Vladimir Demikhov, and for four days the hybrid of two dogs lived as normally as such a scientific horror could be expected to. Then they died.

Demikhov tried the experiment more than 24 times, but was unable to find a way of avoiding the dogs dying shortly after surgery. Although the results are horrifying to see, Demikhovs research did pave the way for human organ transplants.

"For four days this hybrid of two dogs lived as normally as such a scientific horror could be expected to. Then they died."

But back to the topic of head transplants. The first time a straight swap was successful, was by Dr Robert White, in an experiment on a rhesus monkey in 1970. I feel the need to qualify the word successful with quotation marks, because although the monkey did live, he didnt live very long. Eight days, to be exact, and as the spinal cord wasnt attached to its new body, the monkey was paralysed for its remaining days. However, it could indeed see, hear, smell and taste before the body rejected the foreign head.

According to Canavero in his paper on human head transplants, the monkey lived eight days and was, by all measures, normal, having suffered no complications. However, Dr Jerry Silver who worked in the same lab as Dr White has more haunting memories. He toldCBS: I remember that the head would wake up, the facial expressions looked like terrible pain and confusion and anxiety in the animal. The head will stay alive, but not very long. It was just awful. I dont think it should ever be done again.

More recently, Chinese doctor Xiaoping Ren claims to have conducted head transplants on more than 1,000 mice. The Wall Street Journal reports to have witnessed a mouse with a new head moving, breathing, looking around and drinking. But, crucially, none of these mice have lived longer than a few minutes.

Still, Dr Rens studies continue, and the latest reports are said to be promising, offering a possible answer to the risk of severe blood loss (or brain ischemia) during transplantation. The experimental method that we have described can allow for long-term survival, and thus assessment of transplant rejection and central nervous system recovery, bringing us one step closer to AHBR in man, the researchers wrote.

Ren himself has not ruled out taking part in the first human head transplant operation, according to the Daily Mail. "A human head transplant will be a new frontier in science. Some people say it is the last frontier in medicine. It is a very sensitive and very controversial subject but if we can translate it to clinical practice, we can save a lot of lives," he said.

"Many people say a head transplant is not ethical. But what is the essence of a person? A person is the brain not the body. The body is just an organ," he added.

In January 2016, Canavero told New Scientist that a head transplant had been successfully completed on a monkey in China, although details were sparse. "The monkey fully survived the procedure without any neurological injury of whatever kind," he said, although the article notes that the monkey only kept alive for 20 hours after the surgery for "ethical reasons," limiting its use as a comparison somewhat.

In September 2016, Canavero revealeda further trial of the head transplant on dogs.New Scientisthas seen video footage of a dog appearing to walk three weeks after its spinal cord was severed, with Canavero claiming that the outcome is the result of the same techniques he plans to use on Spiridonov next year.

However, speaking to a number of scientists for their view on the new evidence, New Scientistcould find few sceptics converted. "These papers do not support moving forward in humans," said Jerry Silver a neuroscientist at Cape Western Reserve University in Ohio.

"The dog is a case report, and you cant learn very much from a single animal without controls. They claim they cut the cervical cord 90 per cent but theres no evidence of that in the paper, just some crude pictures," added Silver.

You could say so, though Canavero doesn't see it quite like that. In fact, controversially he sees it more as a failure of other types of medicine, telling Medical News Today, "It will be about curing incurable neurological disorders for which other treatments have failed big time, so gene therapy,stem cells- they all just came to nothing. We have failed despite billions of dollars being poured into this sort of research."

"So actually, head transplant or body transplant, whatever your angle is, is actually a failure of medicine. It is not a brilliant success, a brilliant advancement to medical science. When you just haven't tackled biology, you don't know how to treat genes, you don't really understand, and you really need to resort to a body transplant, it means that you've failed. So this must not be construed as a success of medical research," he added.

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