Warning: This post contains spoilers for the movie The Matrix.
Today a tweet by Neuroskeptic pointed me to this post entitled “You are not your brain: Why a head transplant is not what you think it is“. The title initially sparked my interest because it is a topic I have been thinking about a lot. I am actually writing a novel that deals with topics such as the scientific study of unconsciousness, non-free will, and disembodied cognition*. This issue is therefore succinctly relevant to me.
Unfortunately, this particular post does not really deal with this topic in any depth but only espouses a trivial form of mind-brain dualism. It discusses some cherry-picked findings without any proper understanding of current neuroscientifc knowledge and brushes aside most scientific arguments about consciousness as “bizarre” claims, without providing any concrete argument why that is so. Don’t get me wrong, some claims by neuroscientists about free will and consciousness are probably on logically shaky ground, and neuroscientists themselves frequently espouse a form of inadvertent dualism in their own writing about how the brain relates to the mind. However, this post doesn’t really discuss these issues in an adequate way – but go and read it and make up your own mind.
Either way, I think the general thought is intriguing nonetheless. What would actually happen if we could transplant a human brain (or the whole head) into a different body? Let’s ignore for the moment the fact that our surgical technology is nowhere near the point where we could do this with humans and allow the transplanted head to actually control the new host body. Instead let us assume that we can in fact connect up all the peripheral neurons and muscles in the body to the corresponding neurons in the transplanted brain.
Thinking about this already reveals the first problem: there has got to be a mismatch between the number of neurons in the body and the brain. Perhaps this doesn’t matter and some afferent and efferent nerve fibers need not be connected up to the brain, or – vice versa – some of the brain’s neurons need not receive any input or have any targets in the body. If the bulk of the brain is connected up properly perhaps this suffices? In any case, our brains are calibrated to the body and so to place them into a new body must inevitably throw this calibration completely out of whack. Perhaps this can be overcome and a new calibration can emerge but in how far this is possible is anybody’s guess.
A related problem is how the brain represents the body in which it has been placed. Somehow we carry in our minds a body image that encodes the space that our body occupies, how it looks, how it feels, etc. There are illusions that distort this representation of our own bodies. Some malfunction or fluke in that system could also explain some out-of-body experiences although it is of course difficult to study such phenomena. It seems however pretty likely that such experiences should be exacerbated in a person whose brain has been transplanted into a new body. Imagine you are 1.5 meters tall but your brain has been transplanted into the body of an NBA player. Your experience of the world through this new, much taller body must inevitably be far greater than simply looking at the world from your new vantage point. Over a lifetime of existing in your short body you should have no representation of the sensory experiences related to being 2 meters tall, nor of the feats your muscles are capable of when you can slam dunk. It is possible that we can learn to live in this new corporal shell but who can know whether that is the case.
In that sense, there may actually be truth to the claim in the aforementioned post that there is some kind of “bodily memory”. For one thing, the flexibility and strength of various muscles is presumably related to what you are doing with them on a daily basis. Who knows, perhaps the various nervous tissues in the body also undergo other forms of synaptic plasticity we don’t yet know about? Of course, none of this suggests – as this post claims – that much of your self is in fact stored inside your body or that you become the host person. The brain is undoubtedly the seat of consciousness and of much of your memory, including the fine procedural or motor memory that you take for granted. But I think it is fair to say that by having your brain being wired up to a new body you would certainly experience the world in uniquely different ways. Insofar as your perception affects how you interact with the world this may very well alter your personality and thus really change who you are.
In the same vein I also view other thought experiments, such as the common science-fiction notion that we could one day upload our brains to a computer. Even if we had a computer with the data capacity to not only store a complete wiring diagram and the synaptic weights of all the neurons in the human brain and even if neuronal wiring diagrams were all there is to processing in the brain (thus completely ignoring the role of astrocytes, possibly important functional roles of particular ion channel proteins, or of slow neurochemical transmissions), whatever this stores would presumably not really be the person’s mind. Simply running such a network in a computer would effectively cut this brain off from its host body and in this way it would be comparable to the brain transplant situation. It is difficult to imagine what such a brain would in fact experience in silico. To approximate normal functioning you would also have to simulate the sensory inputs and the reciprocal interactions between the simulated brain and the simulated world this brain inhabits. This would be a bit like the Matrix (although that movie does not involve disembodiment). It is hard to imagine what this might really feel like. Quite likely, at least the cruder beta versions of such a simulation would be highly uncanny because they don’t accurately capture real world experience? In fact, this is part of the plot of the Matrix movie because the protagonist senses that something isn’t right with the world.
I find this topic quite fascinating. Whatever the case may be, I think it is safe to say that we are not just our brains. As opposed to the simplistic notion of how the brain works suggested by many science fiction and fantasy stories, our minds aren’t merely software running on brain hardware. Our brain exists inside a body and that presumably must have some influence on the mind. I don’t buy into much of the embodied cognition literature, as a lot of that also seems very simplistic. I certainly agree in large parts with Chaz Firestone and Brian Scholl that it has not really been demonstrated that things like the heaviness of a backpack can affect your perception of the steepness of the hill before you. But at the same time, I think some degree of embodiment must exist, precisely because I am not a dualist. I don’t think there is any evidence to suggest the mind simply floats in the ether, completely removed from the brain and body. Rather it is emergent property of the brain, a brain that is intricately connected to the rest of the body it resides in (and even that is simplistic: I would in fact say that the brain is part of the body).
Coming back to that post about head transplants, the post is on a website called Religion News and the author is a professor of theological and social ethics. As such it is unsurprising that he discusses a dualist view of the mind and criticizes some of the neuroscientific claims that conflict with that notion. However, his argument is quite odd when you dig a little deeper: rather than saying that your self arises in your brain, the author implicitly suggests that is inherent to your body – he literally states that the person whose brain is transplanted dies because they are in a new body. He further suggests that any children the patient would have in their new body would not be his but those of the host body. While genetically this argument is correct, it completely ignores the fact that there is now a new mind driving the body. Whatever distortions and changes to this mind may result from the brain transplant, it is clearly wrong to claim that the host body would completely override the mind inside the transplanted brain. Yes, biologically the children would be those of the host body but mentally they would be the children of the transplanted mind. Claiming otherwise is equivalent to the suggestion that adoptive parents are not real parents.
In conclusion, I agree that there are some interesting philosophical and theological ramifications to consider about brain transplants. If you believe in the existence of a soul, it is not immediately obvious how you should interpret such a case. I don’t think science can give you the answer to that but that is between you and your rabbi or guru or whoever holds your spirituality together. But I think one thing is clear to me: the soul is not inherently attached to your body any more than it is to your brain. No, you are definitely not just your brain. But you aren’t just your body either.
(* Work on this is going very slowly so don’t get your hopes up you’ll see any of this anytime soon – it’s more of a lifetime project…)