The metaphysics of head and brain transplants

Dr. Michael Egnor has recently written a couple of thought-provoking posts over at Evolution News. I’d like to invite readers to comment:

Are Head Transplants Soul Transplants? Full article here.

Are Human Brain Transplants Even Possible?

Head transplantation is interesting from a metaphysical perspective. It’s a question that would have interested Dr. Frankenstein: Imagine that spinal cord repair were feasible and patients would not be rendered paralyzed. If heads were successfully switched, where would the souls end up? Is the soul in the brain, in the body, in both, or in neither? Two people would still exist after switching heads. But who would be who? Where would the souls go — with the brains or with the bodies?

In a head transplant, it seems obvious that our senses would follow our sense organs. If my head were transplanted onto my neighbor’s body and vice versa, my eyes would still be on my original head, so I would see with my original eyes.

What about the “ownership” of the body after a head transplant. If my spinal cord worked after the transplant and I moved the fingers attached to the transplanted body that was attached to my original head, would I be moving my fingers or my neighbor’s fingers?

If my head were transplanted onto my neighbor’s body, I would see, hear, smell, and taste where my original sense organs were — in my head. For abilities that include both the head and body, it seems obvious from anatomy and physiology that I (corresponding to my original head) would feel using the touch sensors in the skin of my neighbor’s transplanted body.

It is theoretically possible to remove the right hemisphere from my neighbor and place it in my skull. Let us assume that my neighbor’s right eye was transplanted along with his right hemisphere. I believe that the outcome can be predicted with confidence. My neighbor would see out of his right eye in my skull. My neighbor would also see out of his left eye in his own skull — he would have double vision, in a real sense. If my right hemisphere and eye were transplanted into his skull, I would have corresponding double vision. This might seem strange — to have eyes in two different locations that see different things. But that is the way we would be then. Our eyes are a few inches apart, and the distance between them permits depth perception. After a hemisphere-eye transplant, eyes could be thousands of miles apart. I would see two superimposed scenes — double vision — in completely different parts of the world, depending on where the skulls that contained the hemispheres and eyes traveled. Obviously this would be very strange, but it presents no metaphysical problems that I can see.


You want serious responses to the idea that if some-one in America underwent a mutual eye transplant with an Australian they would both be able to see America and Australia at the same time?


I think Egnor missed the date. April Fools’ Day is tomorrow.


Egnor’s posts did not provoke much thought here.

This seems quite absurd, and I wonder why Egnor does not see it as absurd. Or perhaps he does, but he sees it as absurd in the wrong way.

But, Roy! Think of the benefits to tourism!


I wouldn’t use that description. Why does Egnor not know that the right eye, through the optic chiasma, connects to both hemispheres, and that each hemisphere gets input from half the field of each eye? And how are the two separated hemispheres of his brain supposed to communicate? Through the soul? Does he end up assuming that the soul is split between two halves of the brain? Sounds like spooky action at a distance.


Do you understand the premise here to be that there is something of consciousness or the self that travels about with the right hemisphere and attached eye? Such that the “neighbor’s” consciousness stays with that right hemisphere when it is implanted into someone else’s head?

I don’t grant that premise, but I also don’t think it’s ridiculous to ask the question, at least for people who believe in souls or other disembodied “conscious” entities. The author is clearly a dualist and perhaps believes in souls and spooks and stuff. I don’t, and I’m sure I’m right, but within the author’s framework these questions seem rational and reasonable to me.

Or am I missing something? Please don’t tell me I’m going soft on dualism.

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You may be missing the claim that a soul can be divided into two halves that can communicate when thousands of miles apart.

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Then it’s good to know that I’m not missing anything, since that was pretty obvious.

My point is that if someone believes in souls at all (I think they’re a silly gloss, an “idea” that’s a bit of an embarrassment to our species), and if they think that souls ride around in meat, then the kinds of thought experiments in the OP are perfectly normal fodder. If some other soul-believer wants to decree that souls can’t be fractionated, then they can register their disapproval while the rest of us laugh and go back to our research on horcruxes.

Assuming head transplants could actually be done, I don’t actually see the absurdity. What else would you expect to happen? Would the neighbour be the one seeing? Even if the neighbour was just beheaded without attaching the poor lug’s head to another body?

Exactly. I’m a bit shocked that a neurosurgeon would not know this.

I will just add that Daniel Dennett, who approaches these questions from the position exactly opposite to Egnor’s, goes thru a similar thought experiment cum science fiction short story in his classic article “Where Am I?”.

I don’t believe in souls, but I would think this would be almost certainly false, even if souls were real. My religious upbringing would have dealt with this problem by denying the possibility of such a transplant at all, which, like the Egnor’s idea, benefits from the transplant being very improbable for the foreseeable future. Either one is a very testable prediction with pretty clear results, which I think is a very risky hook to hang one’s theological hat on.

From just my layman’s knowledge about how brains work and how the hemispheres communicate, Egnor’s view already seems like it’s on the wrong side of science.

Perhaps a soul—divisible in life—yet coalescing back into one in the afterlife might be the best path forward.

You deleted the second half of my post and responded as if it wasn’t there. Are you practicing ID techniques?

This thread makes my head hurt.


If you think “ignoring” and “deleting” are the same thing then the ghost in your machine is confused.

All of my comments in this thread are about concepts that I (and perhaps you and surely others) consider to be batshit crazy BUT that are legitimate to discuss within a particular framework. My question to @vjtorley was serious in that I wanted him/us to consider and/or acknowledge the premise. That premise, as near as I can tell, is that there are soul-ghosts anchored to brain-meat. A further premise, which I think is more than obvious from the OP and thread, is that the soul-ghosts have powers akin to telepathy that operates over distances that have been arbitrarily judged to be vast. And a further premise is that if the brain-meat is subdivided, the soul-ghost will be spatially distributed. These are premises.

Batshit crazy? To me, yes, but to me so is essentially all of Christianity. I think it’s fair to grant someone their premise and discuss what it might mean. Attacking the premise is fair at the outset but then it becomes obnoxious.

In short: this is a forum that includes moderators and participants, in the majority, who believe in things I consider less reasonable and frankly a lot more dangerous than any of this, and they reasonably expect us to grant their framework. I’m willing to do that. Maybe you’re not.

All of it, or just the part your soul is attached to? Presumably it’s all still in your original body, and just one body at that. Or am I wrong?


Re-reading Dennett’s article, I note that despite being the furthest thing from a dualist, he seems to confirm Egnor’s intuition regarding the results of a head transplant, at least initially (His overall thesis, it seems to me, is that the very idea of a “self” that is observing or experiencing the world thru our senses is illusory, which is why it cannot be consistently pinned down to any particular location or perspective.

The context is an experiment in which Dennett’s brain has been removed and placed in a vat, with tiny transmitter/receivers installed in both the brain and the sense organs of Dennett’s body, such that he is able to have sensory experiences identical to if his brain was still inside his head. His body is standing besides the vat looking at his brain thru his eyes, and he is trying to decide where Dennett now is. To help answer the question, he decides to call the brain Yorick and his body Hamlet. So where, then, is Dennett?

Where Hamlet goes, there goes Dennett

This principle was easily refuted by appeal to the familiar brain-transplant thought experiments so enjoyed by philosophers. If Tom and Dick switch brains, Tom is the fellow with Dick’s former body. Just ask him; he’ll claim to be Tom, and tell you the most intimate details of Tom’s autobiography. It was clear enough, then, that my current body and I could part company, but not likely that I could be separated from my brain. The rule of thumb that emerged so plainly from the thought experiments was that in a brain transplant operation, one wanted to be the donor, not the recipient. Better to call such an operation a body transplant, in fact. So perhaps the truth was,

Where Yorick goes, there goes Dennett.

This was not at all appealing, however. How could I be in the vat and not about to go anywhere, when I was so obviously outside the vat looking in and beginning to make guilty plans to return to my room for a substantial lunch? This begged the question I realized, but it still seemed to be getting at something important. Casting about for some support for my intuition, I hit upon a legalistic sort of argument that might have appealed to Locke.

Suppose, I argued to myself, I were now to fly to California, rob a bank, and be apprehended. In which state would I be tried: in California, where the robbery took place, or in Texas, where the brains of the outfit were located? Would I be a California felon with an out-of-state brain, or a Texas felon remotely controlling an accomplice of sorts in California? It seemed possible that I might beat such a rap just on the undecidability of that jurisdictional question, though perhaps it would be deemed an interstate, and hence Federal, offense. In any event, suppose I were convicted. Was it likely that California would be satisfied to throw Hamlet into the brig, knowing that Yorick was living the good life and luxuriously taking the waters in Texas? Would Texas incarcerate Yorick, leaving Hamlet free to take the next boat to Rio? This alternative appealed to me.

Barring capital punishment or other cruel and unusual punishment, the state would be obliged to maintain the life-support system for Yorick though they might move him from Houston to Leavenworth, and aside from the unpleasantness of the opprobrium, I, for one, would not mind at all and would consider myself a free man under those circumstances. If the state has an interest in forcibly relocating persons in institutions it would fail to relocate me in any institution by locating Yorick there. If this were true, it suggested a third alternative.

Dennett is wherever he thinks he is.

Generalized, the claim was a follows: At any given time a person has a point of view, and the location of the point of view (which is determined internally by the content of their point of view) is also the location of the person.

Such a proposition is not without its perplexities, but to me it seemed a step in the right direction. The only trouble was that it seemed to place one in a heads-I-win/tails-you-lose situation of unlikely infallibility as regards location. Hadn’t I myself often been wrong about where I was and at least as often uncertain? Couldn’t one get lost? Of course, but getting lost geographically is not the only way one might get lost. If one were lost in the woods one could attempt to reassure oneself with the consolation that at least one knew where one was: one was right here in the familiar surroundings of one’s own body. Perhaps in this case on would not have drawn one’s attention to much to be thankful for. Still there were worse plights imaginable, and I wasn’t sure I wasn’t in such a plight right now…

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Well, let’s hope no one needs to swap heads anytime soon. :slight_smile:

Some believe the soul and body are tied together. This would definitely cause issues in the case of a potential head swap.

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Many do. Or, rather, there are heads that need healthy bodies to remain alive. The technical obstacles to such transplants may be insurmountable. But if not, it might be a major advance and a boon to humankind.

OTOH, would we really want to become a species largely made up of heads on pillows?

That was my interpretation as well. Which raises the rather odd question of, if you suffer traumatic brain injury and part of your brain dies, does part of you go to Heaven/Hell, whilst the rest of you stays on Earth? :upside_down_face:

Further, if you thereafter sin, or get ‘saved’, can bits of you end up in different afterlives to other bits of you? :thinking:


As I look at it, Dennett is very much a dualist. Yes, he denies dualism, but his entire way of thinking about his relation to the world comes from dualistic ways of thinking.

Yes, he denies the observer. But he does not deny the observing or experiencing.

In a way, his view is similar to that of Berkeley’s idealism. God is observing the world, and piping those observations to him as percepts. I’m sure he would deny this, but his view seems equivalent to this.

I’m surely further from a dualist than is Dennett. Yet I don’t reject the idea of a self. Better to explain it than to reject it.

So my brain has worked out ways of observing and experiencing using my body. The self is in that set of abilities. Transplant my brain to Tom, and you have a problem. My brain can get observations using my body. But it does not know how to do it with Tom’s body. So, after the transplant, there could be no observations, no Tom and no me. The self would be gone, unless the transplanted brain can work out how to do it with a different body. And that’s a pretty tough problem for a transplanted brain to solve.

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