Wired offers a fascinating article about Dr. Robert White, a neurosurgeon in the mid-20th century who was famous for his extensive research on head transplants. He transplanted heads of various animals, often unsuccessfully (many animals died) but with some success, particularly with monkeys. The medical, ethical, and sociological issues are interesting in themselves, but I’ll focus here on the metaphysical issues. Specifically, if your head is transplanted, does your soul go with it?
First, it worth noting that head transplantation is difficult surgery but doable. We know how to sew blood vessels together, how to fuse spinal bones, how to attach tracheas and muscles and peripheral nerves. Transplantation of an entire head (or an entire body, depending on your perspective) would be technically challenging and quite risky.
Head transplantation has not been done on humans. Not because it wouldn’t work — it would be technically easier on humans than on monkeys because humans are bigger so things would be easier to sew. It has not been done on humans because, in order to transplant a head, you must cut the spinal cord, which causes permanent paralysis. Head transplantation causes quadriplegia. There is no real medical benefit in creating a quadriplegic patient — it might preserve life but at the expense of total paralysis. This question occasionally arises in neurosurgery in a different context. The consensus is that deliberate imposition of a catastrophic neurological disability is unacceptable, even if it may save life. With rare exceptions, we don’t deliberately make people blind or paralyzed or comatose, even to prolong life.
An ethical case for head transplantation could be made in the case of an already quadriplegic patient who had multiple organ failure and who would die otherwise. This is a rare scenario.
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?
As with so many metaphysical questions about the mind-body relationship, we need first to understand the meaning of the words we use. The question of the disposition of the soul depends on what we mean by “soul.” Is the soul a thing that lives somewhere in the brain, so to speak, or in the body? Or is it outside the body and brain or somewhere or something else? Or is the soul not a “thing” at all? Does the soul exist?
The meaning of a word, as Wittgenstein has emphasized, is its use. A word gets its meaning from its use. I use the word “soul” to mean what Aristotle took it to mean — the intelligible principle of a living human being. That means roughly that the soul is the organization and function of a living person — the structure and coordination of cells and tissues, organs and body parts necessary for life.
Aristotle used the metaphor of the eye: If the eye were the body, sight would be the soul. So the soul doesn’t have a location because a principle doesn’t have a location, other than the location of the matter of which it is the principle. An eye has a location. Sight can’t meaningfully be said to have a location in itself, other than the location of the eye that sees.
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. If transplanted-head me traveled to China while my transplanted-head neighbor stayed in America, I would see (and hear, taste, and smell) China, while my transplanted-head neighbor would experience the same sensations in America. A function is located where its material instantiation is located — at least that’s the sense of the ordinary language we use when locating a function.
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? It depends on that I mean by “my” fingers and “my neighbor’s” fingers. Do I mean the fingers’ ownership before or after transplantation?
We face this question today with organ transplants. I have a family friend who has had a heart transplant. Is her new heart hers or is it the heart of the young man from whom it was harvested? It is hers if we consider that she would die if it stopped but he would not change status if it stopped — he’s already dead. But it’s his in the sense that it has male chromosomes, which, in her female body, would only be technically a part of her if she were a hermaphrodite.
In real life, these issues don’t arise because we use common sense. It’s her heart, for all intents and purposes, although the young man’s family might feel that a part of their son is still living in her, which is appropriate as well. We sort out these metaphysical questions just by the way we use language. The question “Whose heart is it?” goes no deeper than linguistics. There is no deeper truth to the matter.
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. I could, if I chose, call it my new body or my neighbor’s old body that I now use. It is just a matter of language, not a matter of metaphysics.
We deal with these linguistic conventions with organ transplants now. Does a kidney transplant recipient make urine with her kidney, or with her donor’s kidney? It merely depends on how we wish to say it. Head/body transplants would be no different.
Here’s a more subtle question: What if different parts of the brain could be transplanted? What if I switched right brain hemispheres with my neighbor? Would my neighbor be able to move my left arm while I could move his right arm, and vice-versa? What if my neighbor and I switched speech centers of our brains? Would I speak my neighbor’s thoughts and he speak mine?
These are fiendishly fascinating questions. Interestingly, there are conjoined twins who share brain parts and cooperate in some movements of limbs and even seem to think similar thoughts at times. So this question is not merely hypothetical. Some research has been done on this fascinating topic but it is beyond the scope of this post.
Much of the mystery about head transplants and the soul can be resolved by careful use of language. Linguistic clarity would solve the vast majority of our metaphysical dilemmas, but not all of them, I think.
Next: Are brain transplants possible?
You may also wish to read: Your soul has no “Off” switch It’s an intriguing and important question and you may be surprised by some of the answers. (Michael Egnor)