Head transplantation

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This is version of Vladimir Shakirov (editing rules). Alternative versions of this article would be here. Currently no alternative versions available.

tl;dr

Successful animal head transplantation to its clone/identical twin (with two heads as a result) seems to be possible nowadays. Quite probably, both animals would live for many months if not years thereafter.
This is a reasonable first step in a chain of increasingly more challenging experiments which can lead us to the first successful human head transplantation. For human head transplantation to become really valuable, new bodies should be available in large quantities. This can be achieved by growing immunocompatible (chimeric?) animals, by developing artificial body that would supply blood to brain, or by growing anencephal clones.
Brain ages. However in most cases body fails to function one or several decades before brain fails. Even people of healthy lifestyle mostly die 10-20 years before their late demention comes in. So human head transplantation could give them those extra 10-20 years (if their old brain would endure ischemic and perfusion/reperfusion injury of surgery). There is parabiosis rejuvenation theory though that brain aging could be slowed down if connected to young body. So if we transplant 40yo human head to 20yo body then perhaps it would age with a half of usual speed. So may be in 20 years after surgery biological age of head would be just 50yo? So perhaps a transplantation every say 20 years would give a transplanted head extra 50 years of life? See also: Options for human head transplantation

Is human head transplant surgery possible now?

List of arguments speaking for feasibility:
(1) Head transplantation surgeries on animals have been performed for many decades. As early as in 1950s one of twenty Vladimir Demikhov bicephalic dogs lived for as much as 29 days after surgery (though other 19 dogs lived no more than 7 days)<ref>V.P. Demikhov, "Peresadka zhiznenno-vazhnykh organov v eksperimente", p.144. Medgiz, 1960.</ref>. Importantly, it happened before highly potent immunosuppressors like cyclosporin were developed. See good review of head transplantation history in en.wikipedia.

Here is some brief collapsible summary (click "Expand" =>)

  • 1908 - future Nobel laureate Alexis Carrell grafted dog head to another intact dog. No real consciousness after operation; the animal was killed after a few hours
  • 1950s - Vladimir Demikhov grafted dog head and upper body to another intact dog. He performed 20 experiments. One of dogs lived for 29 days. The animals died due to transplant rejection.
  • 1970 - Robert J. White grafted monkey head to another monkey. The transplanted head even tried to bite researcher. There were four experiments; monkeys died between 6 hours and 3 days after operation.
  • 2012 - Xiaoping Ren grafted mouse head to another mouse. Some of mice lived 24+ hours after that. Wiki falsely claims that one of animals lived for 6 months after that. see criticism
  • Sergio Canavero has published several works with concrete protocols for human head/brain transplantation.

(For more details see List of head transplantation experiments in animal models)

(2) Transplantation of most human organs is common and widespread nowadays, see en.wiki list of transplanted human organs. Modern immunosuppression drugs help to manage transplant rejection. For example, the average heart transplant survival is over 10 years now[1]. Development and usage of cyclosporin A around year 1980 and its analogues later was a defining milestone in effectively defeating immune rejection reactions[2]. There are also examples of successful multi-organ transplantations, for example:

(3) Sergio Canavero et al. have published several works with (not so) concrete protocols for human head/brain transplantation. The most detailed paper is [3] where they performed head transplantation with human cadavers. See also <ref>https://doi.org/10.1007/s40472-018-0196-7, chapters "Surgical hurdles" and "Immunological hurdles"</ref> where surgery and immunosuppression for possible human head transplantation are outlined in detail.

List of arguments speaking against feasibility of human head transplantation in year 2023:
(1) Despite the fact that head transplantation surgeries on animals have been performed for many decades, still there are no successful examples of animals being alive more than month after surgery (or even consistently alive >1week!). The famous dog of Vladimir Demikhov which lived for 29 days is but a sole example out of 20 bicephalic dogs. All other dogs lived no more than 7 days after surgery.<ref>V.P. Demikhov, "Peresadka zhiznenno-vazhnykh organov v eksperimente", p.147. Medgiz, 1960.</ref>
There must be reasons why 2015' research paper[4] of head transplantation in mice by famous-in-head-transplantation-circles Xiaoping Ren has such unimpressive results. As well as why such unimpressive results ("Forty Kunming mice and forty C57 wild type underwent theAHBR procedure. After transplantation, 18 mice survivedfor 3 h after the ventilator was disconnected") where obtained by the same author here in 2014[5]. /though perhaps mice surgery is way harder? the arteries and veins are way smaller/
Anyway it's unlikely that any ethical comittee allows human head transplantation before successful results on animals with at least several months of survival after procedure.
(2?) Transplantation of the head is considerably more difficult than say heart or lung transplantation. For example, many immunosuppressive drugs induce leakages in blood-brain barrier[6], especially so after its initial damage caused by some period of ischemia during surgery and perfusion/reperfusion injury after ischemia<ref>https://pubmed.ncbi.nlm.nih.gov/28130190/</ref><ref>https://doi.org/10.1007/s40472-018-0196-7</ref>. That opens brain for inflammation and infections. (Though what about the same leakages in BBB induced by immunosuppression drugs when we transplant for example heart? The heart does not attacks epithelial cells of brain vessels while new body will do that causing general inflammation so that BBB leakages would be much more vulnerable).
Head transplantation also includes face transplantation which itself is immunologically more difficult[7] procedure than say heart transplantaton. The first face transplant was performed as late as in 2005, and as of 2020 there were only 47 face transplants[8].
Immunosuppression protocols for whole head transplantation are yet to be developed; that might turn out to be easy or hard, nobody knows. Relevant animal experiments should be performed to get hints for that.
(3) Indirect argument is that except for S.Canavero and some of his colleagues (almost?) nobody argues that human head transplantation is already feasible. Importantly S.Canavero and his colleagues do not seem to present high quality papers on the subject. Here is a 2017y article with constructive criticism of Sergio Canavero papers on head transplantation[9]. In brief, the article claims that (a) Sergio Canavero has no decently good papers on the subject of head transplantation (b) key articles of S.Canavero colleagues (like this one[10] with PEG + ultrasharp blades cutting spinal cord) don't have statistically significant results, are not reproducible, are inconsistent from theoretical viewpoint, etc (Ctrl+F "the cut membranes were contiguous" in [11]).

What are main options for human head transplantation?

There are four main options to consider.
(1) Connect head to a living person. Here we find a living person who wants to have another head be connected to own body.
list of possible reasons to agree to be head transplantation recipient
(2) Connect head to brain-dead body.
(3) Connecting head to artificial body
(4) Connecting head to animal body
Which option is better?

If human head transplantation is doable, why nobody tried?

(1) The problems outlined in "Is human head transplant surgery possible now?" In brief, as there are almost no examples of animals living more than 1 month after transplantation (and even 7days+ examples are scarce), there is a reason to believe that transplanted human head would not live much longer.
(2) The large part of the problem with human head transplantation is supposedly low quality of life after the operation. A person will not be able to control or sense the body in the usual way. However:
(2.1) it's something many people with complete spinal cord injury live with. Here is Reddit AMA of person with C4 complete spinal cord injury. He works as a programmer, has received B.S. and PhD after injury. Here's quotation of him: "I can slowly type on a keyboard with one of my knuckles, but I usually use voice software for typing. I've been using Dragon NaturallySpeaking for the last 11 years.". Here is quotation of another person in that AMA: "Nice work on the degrees! I'm a C5 quadriplegic, and have been for 13 years. I earned my PhD last year, and have a tenure-track faculty position at a state university". Nevertheless this kind of will is not for everyone. AI development brings some good hope though. We can try to control legs, hands and even fingers through neural interfaces (there is a video where quadriplegics could even somehow walk through BCI) as well as commands to all sorts of helping robots can be used.
(2.2) If we transplant head with two hands and corresponding part of spinal cord, transplanted head could control and sense hands which is a big relief. If it is technically possible for operation and energetically possible for the recipient person.
(2.3) If we transplant head to another person, the part of contract may suppose that the recipient person has to fullfill wishes of the transplanted head to some extent (anyway this is easier part of the contract compared to the operation itself and its medical consequences).

(3) The other related problem is phantom pains. As Sergio Canavero himself wrote, "the possibility of the transplantation setting off a heinous pain syndrome that would have negated the final result"[12]. In that article he proposes a possible experimental solution based on his own theory of phantom pains but it's all just hypothetical solutions which need experimental verification.
(4) Another obstacle is relatively small number of possible clients for head transplantation. The operation itself is very expensive (~$10mln to ~$100mln) and complicated, and highly experimental (so risky for both transplanted head and recipient person), while life quality after transplantation is mediocre at best (though arguably better than nothing).
Also the head transplantation isn't indicated when the problem can be solved f.e. with just heart transplantation. Here is list of possible reasons to agree on own head transplantation. So there is a challenge to find a wealthy person who would need such operation and who would agree.
(4.1) Marketing wealthy people is a problem in itself.
(4.2) The person would probably agree only if transplantation organization looks already serious enough, has some credentials, good team of surgeons etc. While to look serious enough etc organization has to have resources in the first place and it might be hard without special (and quite large) financing. So we get the chicken and egg problem here. S.Canavero and some other people try to solve it though.

(5) It might probably be a problem to find a team of surgeons who agree to make such transplantation.

(6) It might be too difficult or impossible in some countries for legal reasons.

Overall, head transplantation could have been performed already if we had either very motivated wealthy person who pays some ~$10mln to ~$100mln to prepare and perform such operation or some very motivated organization (like perhaps S.Canavero with colleagues) that succeeds to find such more or less motivated wealthy person. However as there are no really successful animal head transplantation experiments, there is reason to believe that it probably would be a failure: person would live just several days/weeks/maybe months in low life quality.

Why head transplantation is interesting for life extensionists in the first place?

It's really tempting to think that everything below the head can be renewed via head transplantation.
Before head transplantation you have old heart, old lungs, old kidneys, old muscles etc.
After head transplantation you have everything new and young... except the head.
While head transplantation operation is very complicated it's still arguably can be easier than multiple organ transplantation operations.
We probably can also make records on mouse life extension with that. Mice die from cancer most often. If old mouse head has a new body that new body has new several years of life without cancer ahead. In head, the cancer is arguably less probable.

Will successful head transplantation be a breakthrough that boosts life extension research?

It really depends on details and results of head transplantation. Let's discuss some options:
Succcessful animal head transplantation with a considerable part of animals still alive 6 months after procedure would be a major paper in a good journal with many citations and much respect. I think it's something researchers should begin with.
Successful human head transplantation to another human (resulting in human with two heads)... it might happen to be just another ultra-expensive treatment in the long row of other such ultra-expensive treatments (like heart transplantation with ~$1.6mln cost or costly CAR T-cell therapies), with no major influence on life extension field (though with much fame for the team who performs it first). It's perhaps only when human head could be transplanted on animal body, then that procedure might began to gradually become less expensive and have some real impact on life extension field.
Successful human (or animal) head transplantation can boost the topic of anencephal clone growing, or may be of immunocompatible animals growing. Though heart/etc transplantation also can benefit from anencephal clones/immunocompatible animals and experiences a constant shortage of organs so reasons exist already and human head transplantation would just add another one reason.

Proposed animal head transplantation experiment

Head transplantation to HLA matched monozygotic twin or clone would remove (or at least greatly alleviate) any immunological issues.
Such experiment would be a good initial step. The next steps might be:
(2) Head transplantation in not fully HLA matched animal twins/clones
(3) Head transplantation in fully HLA matched dizygotic animal twins/clones
(4) Head transplantation in not HLA matched dizygotic animal twins/clones
(5) Head transplantation in animal close relatives
(6) Head transplantation in genetically unrelated animals
etc, gradually increasing immunologic distance between animals and developing optimal immunosuppressor protocol.
Overall this sequence of experiments might result in a sequence of high-impact scientific papers.

Estimated timeline of experiments could be like: (1) if there is no possibility to buy adult clones (that would probably be expensive), one needs to order cloning (f.e. cloning dog in Sinogene costs $50k but it's probably possible to do it much cheaper) and wait for one to several months. (2) operation and at least ~month follow-up after operation. So it's just about several months for an experiment if everything works fine.

Supposedly it's only after successful experiment (5) or (6) when professors in transplantology would probably begin to say that something relevant to human head transplantation begins to happen.
What animal suits the first animal head transplantation better?
Ethical committees could be upset about experiment with transplanted animal head living many months in such stressful circumstances. Standard experiments where aim is to extend lifespan/healthspan of animal would be preferred much more.
The more so, if we consider following experiments in chain (2)-(6). They require perhaps thousands of animals living for many months with a head (probably with upper extremities) separated from their bodies.

Is it better to transplant brain without, with or with some part of spinal cord?

Note that spinal cord is not defended with blood-brain barrier so more open for immune rejection. Spinal cord is defended with spinal cord - blood barrier, but it's more permeable.

Miscellaneous

Petr Kondaurov was seriously preparing to do a head transplant (beginning with mice), but postponed it in July 2022.

This 2019y review about human head transplant was strongly recommended in RLE telegram chat.

Human brain consumes ~20% of human energy consumption [13] so extra human brain poses a considerable extra energy requirement. Moreover it should better be glucose-derived energy.

In 2015, mice were sewn a second head. Out of 40 pairs of mice, 12 pairs lived 24+ hours after transplantation (the operation itself lasted 4 hours), although authors write that mice "regained consciousness, displaying activity function and responsiveness" only 1.5-2 hours after the operation [14]

Our brain also ages. There are numerous aging processes in the brain including atherosclerosis, vascular dementia, middle cerebral artery disease, tauopathies, crosslinking (f.e. amyloids), leukoaraiosis, etc. So head transplantation gives an extra decade or maybe sometimes several decades but aging ultimately should be defeated in brain. However most deaths occur due to brain-unrelated reasons (like heart diseases, most cancers, COPD late stages, pneumonia etc) so head transplantation can gift person some years that can be needed to live to the longevity escape velocity. Also some researchers think that brain is inherently more durable than the rest of the body and can outlive the heart or lungs for one or several decades.
Still, for overwhelming majority of people now and in the nearest future head transplantation would be unavailable until some real progress in tissue/organ engineering/artificial organs/immune-compatible animals happens. And when it does happen, multi-organ transplantation operations would arguably be more preferrable by people than head transplantation though in a little bit more distant future the division between them would gradually disappear.'

TODO:

  • find more articles about animal head transplantation. Do they really never succeeded in living more than a month after surgery?
  • why no one succeeded in >month (or even consistent >1week) living after head transplantation? Hard question to answer because after Demikhov there were only several (poorly described) experiments, and Demikhov had all the reasons to fail (but still is unbeaten champion).
  • read about bicephalic head transplantation (esp. problems of)
  • read about specific problems of head transplantation relative to other organs
  • read about specific immunology problems of head transplantation
  • read the most recent articles of S.Canavero and colleagues (as well as most recent articles on head transplantation)

Some links from this article

List of possible reasons to agree to be head transplantation recipient
List of possible reasons to agree on own head transplantation
List of head transplantation experiments in animal models
Options for human head transplantation

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