Off With Their Heads!

neuronerd

4 years ago

Hold on to your socks, because we’re in for a wild ride. Every so often, news about a certain neurosurgeon and his “brilliant” ideas of human head transplantation make the rounds. I’ve been ignoring them until now in a delusional attempt of thinking that, if no one engages with wacky ideas, they’ll eventually die down. But just because scientists don’t bother with him, it doesn’t mean that the media won’t. And over the last few years I’ve seen the narrative switch from “wow, what a ridiculous idea!” to “human head transplant coming soon to a store next to you!”. What the hell, guys? So I think it’s time to sit down and address what this is about and why it’s so incredibly ridiculous.

Now, if you’ve never heard of Sergio Canavero, consider yourself lucky! Sadly, whether you like it or not, your luck has now run out. So…

Who is Sergio Canavero and what does he want?

Sergio Canavero is a guy with an idea. A stupid idea, but we’ll get to that soon. He is an Italian neurosurgeon who trained and later worked at the University Hospital in Turin until his contract termination in 2015, when he gained notoriety for some wild claims. His mission (and the reason why the hospital distanced itself from him) is simple: he wants to make human head transplantation a reality.

Inspired from Frankenstein, the idea is, in theory, equally straightforward and disturbing: take a functional head stuck to a dysfunctional body (for example, that of someone suffering from some type of muscular dystrophy) and stick it on a functional body with a dysfunctional head (that is, of a brain dead person). The more pedantic among you probably already noticed that, technically, it’s not a head transplant, but a body transplant. However, in Mr. Canavero’s own words: “head transplantation, body transplantation, whatever.” Who wouldn’t trust such a doctor, am I right?

In practice, there are a number of reasons why it’s stupid. In what follows next, we will try to address at least some of these reasons, but, of course, with such a complex procedure, there are many more hidden variables which need to be considered, so keep in mind that this is not an exhaustive list. With that being said, we will consider three main groups of issues:

good scientific practice issues (page 2)
implementation issues (page 3)
ethical issues (page 4)

Good scientific practice issues

These are arguably quite boring when the topic at hand is so bombastic, but they are crucial for further guiding our understanding of subsequent issues, so bear with me for a bit.

Good scientific practice refers to a set of core values that all scientists have to abide by if they are to be taken seriously. That includes being transparent with their work, properly documenting their research, following laws and regulations relating to their research, being open to criticism from their peers, and collaborating with their colleagues. In this context, it quickly becomes apparent what the good scientific practice issues regarding Canavero’s head transplantation are: all of them.

Sergio Canavero has not published his findings in any respectable scientific journal, instead choosing to present most of his ideas in a vague manner through a medium widely known for its scientific rigour: the TED talk. The few “papers” that he has put out were published in sketchy journals and are nothing more than a collection of loosely related, wishful thinking ideas grounded in misread, misinterpreted literature. They read less like the work of a reputable scientist and more like that of a tired undergrad haphazardly throwing words on a page minutes before the submission deadline, desperately hoping that enough “sciency” words and a list of references will elicit a crumble of mercy from their professor and they will finally pass the course. After all, who has time to check whether what you have cited actually supports your statements?

Instead of responding to the pertinent questions and criticism from his peers with proper data, Mr. Canavero has chosen a faster, although arguably more problematic route. He has framed himself as a misunderstood, unfairly shunned scientist. Both an unsung hero and martyr, if you will. Someone whose genius is simply ahead of its time. To support his allegations, he has tried to draw on historical precedent. But for every Ignaz Semmelweis (i.e. for every scientist who rightly went against the status quo), there are a dozen Andrew Wakefields (i.e. quacks that have been systematically debunked). Just look up pseudoscientific theories on Wikipedia and you’ll see what I mean.

He and his admirers fail to consider that the scientific process, in particular when it involves humans, has become more rigorous exactly to prevent people like Mr. Canavero from trying to roll out completely untested and dangerous procedures. Even if we were talking about something more palatable, for example, a kidney transplant, the same issues would remain: it would be unethical and unscientific to randomly start swapping people’s kidneys without extensive studies which demonstrate the safety and feasibility of the procedure.

But if James Bond movies have taught us anything, it’s that, when you have a mission, morals and laws are just nuisances to be artfully circumvented. And as already stated, Sergio Canavero is a man with a mission.

Implementation issues

So let’s move on to the juicy part: the practical problems. Remember when you were a child and you’d swap Barbie and Ken’s heads just for fun? Maybe threw in some extra glue to make sure it held? Well, transplanting a human head onto a new body is absolutely nothing like that.

Brain blood supply

Main problem

One major difference between the human head and that of a doll is the extensive circulatory system which transports oxygenated blood from the lungs to the brain and the other tissues in the area. Now, here’s a boring anatomical fact that didn’t make the TED talk: the lungs are in the chest. And to make matters even worse, the brain can only go without oxygen for about five minutes. Afterwards, the lack of oxygen will permanently damage it.

But Canavero is a genius, so of course he thought of this. His plan is to cool down the body (and the head) to ~10°C. To be fair, lowering body temperature slows down the metabolism and allows the brain to resist for a longer time without oxygen. This is a technique called therapeutic hypothermia and it’s actually used during some cardiac surgeries. Of course, it carries quite a few risks: it increases the chance of infection, it affects the way medication works, it induces changes in the cardiovascular system etc. But carefully considering the risks affecting your patient and not subjecting them to unnecessary ones are minor details when you’re revolutionizing medicine.

Secondary problems

The bigger problem is that it’s not magic, so it doesn’t slow down time by as much as you want. Studies estimating the safe duration of oxygen deprivation during deep therapeutic hypothermia (i.e. between 10°-20°C) based on mathematical calculations have concluded that anything above 30-40 minutes would lead to severe and irreversible neurological damage. In other words, one would have at most 40 minutes to detach the head from its original blood supply, maybe do something about the spinal cord while they’re there, and reattach it to the new blood supply. This alone would be enough to discourage any reasonable person from claiming that head transplants are a year or two away. But Sergio Canavero is an optimist.

In his “paper”, he writes that 45 minutes under deep hypothermia leads to no neurological damage, “with a slight increase on approaching the hour”. More than that, once the body has been cooled down, it needs to be rewarmed. Studies suggest that one should aim for an increase of 0.2°-0.25°C per hour in order to avoid complications such as swelling of the brain and seizures. Yet Canavero’s optimism triumphs over this as well: he doesn’t plan to lower the temperature of the donor body and instead he hopes this body would rewarm the head “in minutes”. Granted, we don’t know what the effects on the brain would be, because no one has studied anything similar before, but hey, if we cross our fingers hard enough, it’s definitely going to work, no?

But wait, there’s more. You know how once the oxygenated blood has reached your brain and dropped off the oxygen there, it also needs to go back to the lungs to pick up more oxygen? Well, the one head transplant attempt in monkeys found a small problem here: even though the veins in the neck were sutured back together, the blood couldn’t flow out of the head anymore because there was a big scar which developed there. Canavero’s solution? Throw in an irrelevant sentence after mentioning the problem, then conclude he will use the exact same method that didn’t work in the monkey for reconnecting the veins in the human transplant. Told you he was an optimist.

Spinal cord reattachment

There are probably other problems regarding the head blood supply, but I’m no vascular surgeon (and neither is Canavero), so let’s move on to his area of expertise (you know, with him being a neurosurgeon and all): reattaching the spinal cord. You would think that, given the millions of nerves in the spinal cord, as well as its importance for movement, the plan would be incredibly sophisticated. But that would mean you have not been paying attention. Canavero is all about simplicity. In his own words: “You cut the spaghetto, you apply PEG, and boom.”

Confused? He probably is too.

Let’s try to unpack. PEG stands for polyethylene glycol. PEG is a versatile substance with many uses, including as the basis for many laxatives, as an excipient in certain medications, as part of cosmetics, and even as a preservative for historical artifacts. As great as PEG is, however, it does not magically glue spinal cords back together. There are some animal studies which highlight the potential of this substance for promoting axonal regeneration in the spinal cord (and thus fusion of the severed parts), but, as usual, the full story is more complicated.

For one, PEG needs to be optimized for this task. It’s not enough to take the substance by itself, throw a handful at the spinal cord, and hope for the best. One has to consider how this substance interacts with the biochemical environment in which it is placed and adjust its physical and mechanical properties accordingly. As you can imagine, no such studies have been conducted in humans and it is unclear whether findings from animal studies would translate well, in particular because there are quite a few differences in terms of axonal regeneration capabilities between humans and animals.

Additionally, even in animal studies, the spinal cord fusion is not complete, with only some axons fusing together. Of course, this means that the animals do not regain full range of motion. Although Canavero casually bypasses the problem, there is something even more concerning: it is unclear whether this partial fusion could lead to long-lasting pain or any other side effects. So while PEG might prove to be useful in spinal cord fusion, we are looking at years, if not decades, of research including both animal studies and human clinical trials.

Seemingly randomly, Canavero is also intent on using electrical stimulation of the spinal cord. I must admit that I am not entirely certain why, but based on current legitimate literature, two possibilities are apparent: to promote axonal fusion or to improve locomotion.

Regarding the first one (i.e. promoting axonal fusion), there are some animal studies which suggest that applying PEG together with an electric field at the site of spinal cord injury yields better results in terms of fusion. Again, this needs further research and validation in humans.

The second possibility, that of improving locomotion, is actually a very active and promising area of research and deserves a post by itself. But to keep it brief: this field focuses on developing electrical stimulators which can be implanted in the spinal cord, below the injury, and which can restore movement for people with spinal cord injuries. One prominent laboratory is that of Grégoire Courtine, a French neuroscientist at the Swiss Federal Institute of Technology Lausanne (EPFL). In the last decade, him and his team have made several majors breakthroughs. They have discovered that successful stimulation delivered by such implants needs to preserve proprioceptive information (= information about limb posture in space). Additionally, they have made improvements regarding the positioning of the electrodes in the spine. And last, but not least, they have integrated this knowledge into designing implants which were subsequently tested clinically. The results speak for themselves.

While brilliant, it is unclear how this method fits into Canavero’s approach and why he needs it in the first place. If his spinal cord fusion works, patients shouldn’t remain paralyzed. If it doesn’t work, then what’s the point of the head transplant?

The brain death problem

And the issues don’t stop there. Before the procedure even begins, there is a “small” hurdle: where does the donor body come from? While there is an ethical aspect to this question, which we will address below, here we are still focused on the technical part. Canavero claims it will “probably” come from brain dead people. But “brain dead” does not equal “patiently waiting for a new head”.

As grim as it sounds, brain dead means dead. And when the brain dies, even though blood oxygenation is maintained through mechanical ventilation, the body gets the “not alive anymore” signal and begins to pack up. That translates into things such as: immune system hyperactivation, increased blood pressure, altered hormone levels, changes in body temperature, and altered lung function. And if that person was an organ donor, all of these changes are problematic and need to be managed through difficult and critical medical management protocols which ensure organ viability. Some of the organs might not survive enough to be transplanted. Some might not have been viable to begin with, because people don’t usually die from being healthy. To give you an idea of what doctors are working with: lungs are only viable in 10-20% of the cases.

But if you want to transplant the entire body, then everything needs to work well. As we’ve already outlined above, the chances of that happening aren’t too great to begin with. Add to that the chronic shortage of organ donors, the fact that the donor and recipient have to match with respect to skin tone and body size, as well as the fact that transplant organs tend to go to people who actually need them and not to fringe neurosurgeons trying to enact their favourite book, and you’ll have another hit on the “why head transplantation is stupid” Bingo card.

Minor issues

Even if everything discussed above is resolved, there are a couple of “minor” issues remaining. Things such as immunorejection, potential mismatches between the brain and the body in terms of fine movement control, and psychological issues related to seeing one’s head on a foreign body. To be clear, there is nothing minor about these problems, but given the magnitude of those above, they really seem like the least of Canavero’s worries.

In terms of immunorejection, it is a known fact that transplanted organs are attacked by the immune system, so patients have to be on life-long medication which suppresses immune system function. Not only does this have a number of adverse effects, but sometimes, the organ is slowly rejected anyway and has to be replaced. Based on intention, the organ is the body, but based on size, what if the immune system of the body ends up rejecting the head?

Regarding control mismatch issues, it is also a known fact that the body and the brain develop in tune with each other. For example, a violinist and a software engineer will have different groups of highly developed muscles, and this will be reflected in their brains. Can a brain that has been trained a certain way its entire life take over a completely differently developed body? As everything else in Canavero’s plan, unclear. And what happens if it can’t take over? What would the functional and psychological impact of that be? Also unclear.

Finally, limb transplants have made it clear that adapting to a new body part is psychologically challenging. Even patients who underwent extensive psychological screening and were offered professional support could sometimes not get used to the foreign limb. So there is no reason to doubt that this will happen in the case of head transplants. The solution when it comes to transplanted limbs is fairly straightforward: remove them. But what can one do in the case of a body?

Ethical issues

The last set of issues concerns ethics. In other words, even if you could do it, should you?

There is no doubt that the idea of head transplantation evokes a knee-jerk reaction of uneasiness, disgust, maybe even fear. But beyond being gross, crazy, or stupid, there are pertinent questions to address before pursuing it.

The first one is: would it be ethical from a medical perspective to subject someone to this procedure? We know that virtually all medical procedures carry some risk. But we also know that, when such a procedure is recommended to a patient, the benefit outweighs the risks. For example, heart transplantation is no walk in the park. However, doctors routinely perform it because the alternative for their patient would be rapid death. On the other hand, being paralyzed from the neck down, while incredibly limiting to one’s life, does not pose the same threat as a failing heart does. Even if we are talking about patients with muscular dystrophies, which have lower life expectancy, it’s still not the same kind of urgency. In that case, would it be ethical to subject them to an incredibly risky, most likely deadly procedure?

And what about using it as a form of life extension? When he gets bored with the rest of bombastic claims, Canavero switches it up by suggesting that, one day, his “pioneering” head transplantation approach will be used to achieve immortality. Leaving aside the fact that the brain would continue to age, this brings up another issue: where would the bodies come from?

We know for sure that there aren’t enough brain dead donors. And especially if you’re going for immortality, you want a young, healthy body, which, again, that of a brain dead person wouldn’t be. Could this give rise to some sort of dystopian scenario?

Ethical questions rarely have a single clear-cut answer. Carefully thinking about them means considering all potential implications, weighing benefits and costs, and generally going beyond sci-fi claims such as “Cloning will come into play”.

To sum up

Is a head transplant actually possible? No. But will it be possible in a couple of years? Also no. Head transplantation is not only a creepy, but also an incredibly unfeasible idea, nowhere near becoming reality. The media attention given to Sergio Canavero, and especially the lack of critical debunking of his wild statements is disappointing.

Fortunately, independent of that, there are research questions with a lot of merit, such as: spinal cord reattachment and transplantation, electrical spinal cord stimulation, treatment of muscular degeneration etc. Objectively, each one of these has the potential to be more successful, less gruesome, and benefit more people than making Frankenstein’s monster into reality. And luckily, serious researchers are striving to make progress in these directions every day.

Disclaimer: even though this article makes it sounds like Mr. Canavero stole my cat, I don’t have anything personal against him. I have never met him, but based on his appearance in the media, I do consider him a clown. Should his future endeavours prove me wrong, I shall take it back. Until then, use your heads while you still have them.

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