Sergio Canavero is adamant that human head transplants will work. In fact, he claims that he could complete such a transplant within a year, and he says that he has the science to back it up. But does he?
Towards the end of 2017, Canavero's project made headlines when the Italian surgeon claimed that he had actually already performed the procedure, which he calls the "head anastomosis venture" or HEAVEN.
Subsequent reports determined that no such procedure took place and that the work was completed on corpses - many neuroscientists question whether even that much was really done.
Most scientists question whether there has been enough scientific progress to allow Canavero to perform such an operation next fall in China, as he claims he will do.
In fact, they question whether research will make head transplants a viable option even in the foreseeable future.
Richard L. Harvey, Northwestern University associate professor of Physical Medicine and Rehabilitation, sums the current consensus: "At this point, it would not be possible to connect the brainstem to the spinal cord in such a way as to get function. So if this were done, the person would be a [quadriplegic]," he told Futurism.
"We can't even repair spinal cords in patients with spinal cord injury, so we certainly can't do that [successfully perform a head transplant]."
But that doesn't mean that we will never be able to do one.
Ralph Adolphs, Bren Professor of Psychology, Neuroscience, and Biology from the Biology and Biological Engineering (BBE) division at the California Institute of Technology (Caltech), doesn't rule out the possibility that a head transplant could be successful in the distant future, although the procedure would have to overcome substantial challenges.
"I don't see any impossibility in principle, so it's conceivable it can be done in the future - but it will happen in small steps first, like curing paralysed people, and you'll be sure to hear about it as all the problems required are solved," he told Futurism.
While, for the time being, a head transplant remains out of reach, if science does advance enough to perform one successfully, it will raise an array of new, mind-boggling questions.
For starters, what happens to the transplanted head in the new body? Because of the way that other parts of the body impact our neurology and the way that we think and act, would joining a head with a new body create a new person altogether or would the head retain its former consciousness unaltered?
Recent studies have shown that mental activity can be influenced by forces outside of the brain. Researchers have been trying to put together a clearer picture of how the body's microbiome - or bacterial ecosystem - affects how people think and feel.
A study has shown how it's possible for gut bacteria to communicate with microbes in the brain. A healthy gut microbiome, for instance, is said to have an effect on the development of anxiety or anxiety-like behaviour.
With a human head transplant, the head would be introduced to a foreign microbiome through the new body. Would this affect how the person thinks?
"[D]ifferent gut bacteria may make you feel different, and therefore think a little differently, but they won't directly make you think differently because all thinking happens in the brain, not the gut," Adolphs said.
"Different gut bacteria might make you more or less groggy or change your mood - just like if you had a cold or not. So I guess the answer is: slightly, and only indirectly, like how viruses or bacteria do when you have a cold."
Assuming that a human head transplant could work, the patient would still need a significant period of recovery for brain activity to normalise. According to Adolphs, this recovery process would be two-fold. It would probably begin with the brain adapting to its new body.
"Just like learning to ride a bicycle, you'll need to learn how to walk and move your arms, and for that matter breathe and regulate your heartbeat," he explained.
It would take several months for brain and body to integrate. However, "that means your brain will change," Adolphs said.
This change is comparable, on a smaller scale, to how people learn to play a musical instrument, and get better with practice - only in this case, it would be practicing to control a new body.
"[Y]ou would change as a person in a number of respects because of a massive reorganisation in your brain as it learns to adapt to your new body […] There would be limits to this reorganisation that depend, among other things, on age," Adolphs added.
Felipe De Brigard, an assistant professor of psychology and neuroscience at the Center for Cognitive Neuroscience of Duke University's Institute for Brain Sciences, has a more radical perspective on the issue.
He told Futurism that "it is unlikely that all of our psychological traits are uniquely dependent upon the cells confined within our head - it is likely that many of our psychological traits are dependent upon the informational transactions between our brain and our bodies.
As such, a change in body would likely alter some of those psychological traits." De Brigard admitted, however, that it's not clear as to what extent a "new body" could alter psychological traits.
Arthur Caplan, founding head of the medical ethics division at the NYU School of Medicine, told Futurism that what would come after a successful head transplant would be as traumatic as the surgery itself.
"Putting a new head in a body is a guarantee of madness at best. The new mind-body integration would never work," Caplan said.
He asserts that this will be the likely outcome, as the brain would be flooded with chemicals and signals from the body that are foreign and unfamiliar.
Harvey explains that, if not to outright madness, the person who'd come out of such a surgery would be the person who owned the head.
"So in a real way it would be a body transplant, not a head transplant," he said to Futurism.
Kai G. Zinn, Howard and Gwen Laurie Smits Professor of Biology at Caltech BBE, seems to disagree with this assessment.
"If it could be done, the brain itself would be the same. But since it would be connected to a different body the person would be very different," he said.
Though they may disagree on the specifics, scientists agree that a human head transplant would be a cognitive nightmare and that the person who'd come out of such a procedure would be that person who owned the head, but with very different, and possibly damaged, brain functions.