The idea has been around for awhile. Rodolfo Llinás had the idea in the mid-2000s; you can see him in the astonishing video above (c. 04:45 ff.). Christof Koch has recently speculated about it in Nature . But Elon Musk is by far the most visible proponent of direct brain-to-brain thought transfer. While he said nothing about it in the recent demonstration of the technology his Neuralink company is developing , he has mentioned the idea in recent conversation with Joe Rogan  and in a long article by Tim Urban .
There are two problems with this idea. We don’t know how to build the necessary technology. Such technology would require millions upon millions of connections (100s if not 1000s of times the number hairs on a head) between two brains, connections that have to go into the brains without shredding them to itsy-bitsy smithereens. However challenging the technology problem is, that isn’t the deepest problem. The deeper problem is one of fundamental principle. The idea of physical thought transfer between brains as so poorly defined that it is difficult to impossible to evaluate. At the moment it is a nonsense idea, one of those ideas that isn’t even wrong.
The principle is easy to understand. I explain that in the next section, using Koch as an example. If you find that convincing then you can skip the rest, perhaps sip some nice tea, or some scotch, whatever suits your fancy. If you’re still curious, I can offer you a look inside a simple nervous system and an account of how Musk misunderstands the nature of linguistic communication. I conclude with some thoughts about dreams of the future.
Christof Koch and brain-bridging
In his most recent book, The Feeling of Life Itself , Christof Koch asks us:
Imagine a futuristic neurotechnology, brain-bridging, that safely reads and writes billions of individual neurons with millisecond precision. Brain-bridging senses the spiking activity of neurons in the cortex of one person and synaptically links this to neurons in the corresponding area in the cortex of another person and vice versa, acting as an artificial corpus callosum.” (p. 236)
The cerebral cortex is the portion of the brain closest to the skull. It is basically a sheet of neurons 2.5 millimeters thick (roughly a tenth of an inch), plus or minus, that is folded up so it can fit inside the skull. Each neuron is a living cell. The brain is roughly symmetrical left and right, as is our whole body, and the corpus callosum is a large bundle of neural fibers, 200 million of them, connecting the two cortical hemispheres. Koch is proposing to connect millions of neurons in one person’s brain with millions of neurons in another person’s brain.
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To understand what this involves it is helpful to know something about neurons. If you’ve already been through Neuroscience 101 or just want to get to the good stuff, you can skip the next two paragraphs.
Neurons are all built on the same plan. Each has a cell body, a single axon though which it transmits impulses to other neurons, and multiple dendrites which receive impulses from other neurons. The size and shape of cell bodies can vary, and the length of axons can vary quite widely. Some may be less than a millimeter long, others, however, have to reach from the brain all the way down the spinal column. Dendrites are all very short and the number of dendrites varies greatly across different neurons.
Neural impulses, or action potentials, are generally called spikes. They are simple electrical impulses having roughly the same amplitude, about 100 millivolts, and the same duration, about a millisecond. Spikes travel from a neuron’s cell body along the axon to a synapse, which a juncture where the tips of axons and the tips of dendrites meet.
However, axons and dendrites do not connect like wires in an electrical circuit, where the circuit is fully insulated, including the junction between connecting wires. The synaptic space is small, but it is open. Axons and dendrites do not physically touch. Rather, neurotransmitters travel across the synaptic gap between neurons. The junctions between neurons are thus leaky. An electrical device wired like neurons would short out as soon as it was turned on.
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So, we’ve installed a brain-bridge between two people. We activate the bridge and each person immediately begins receiving impulses from the other. How does a neuron tell whether an incoming spike is from an endogenous neuron (i.e. from the same brain) or from an exogenous neuron (i.e. from the other brain)? Spikes are not like messages based around on scraps of paper in a school classroom where a message might be identified by a signature, or initials, or merely a whispered message, Juliet sends this to Romeo. As one spike is pretty much like another spike there is no way to differentiate between them.
Things might be different if brains were like computers and came equipped with extra input/output ports. Any spike coming in through one of the input ports would automatically be identified as exogenous. But brains don’t have open I/O ports, so that won’t work.
Now that Romeo and Juliet are linked through a brain-bridge, what happens? Each is flooded with millions of spikes from the other. How can those spikes possibly mean anything to either of them if their brains can’t tell the difference between endogenous spikes and exogenous spikes ?
Let us brain-bridge your and my cortex, starting with a few wires linking our visual cortices. When I look at the world, I see what I usually see but now with a ghostly image of what you see superimposed, as if I’m wearing augmented reality goggles. How vividly and what aspects of what you see I experience depends on the details of the cross-brain wiring. (p. 237)
How can he possibly know that? That is what he would like to happen, but I find it very hard to believe that anything like it would happen. I don’t know what Koch means by “a few wires” in this context, but since he wants these wires to convey at least a ghostly image I’d guess he’s thinking of hundreds of thousands. From a brain’s point of view there’s really no difference between receiving hundreds of thousands of inputs to the visual cortex from the cortex of another brain and hundreds of thousands of inputs from a neuroscientist running an experiment. Remember, these neural impulses aren’t substantial messages, they’re simple spikes. As long as the artificial spikes have the same electrical characteristics as real ones, there’s no difference between the two situations. And even if they were significantly different, there’s no brain mechanism to say: You’re a strange spike. You must be foreign. Wait over there.
The best I can imagine in either of those situations is that one would experience blurring and instability in the visual field, maybe flashes of light, thousands of them, who knows? I can also imagine total visual chaos, an inability to see anything at all but meaningless patterns of light. What Koch wants me to imagine, a ghostly exogenous image from the foreign brain superimposed on a substantial endogenous image, that seems implausible.
But what, but what about…
I know, I’m getting to that, in the next section.
Koch then goes on to crank this fantasy up to eleven. He imagines that “as more and more neurons are interconnected (probably on the order of tens of millions)” the two minds will fuse into one:
At that moment, your conscious experience of the world vanishes, as does mine. From your and my intrinsic perspective, we cease to exist. But our death coincides with the birth of a new amalgamated or blended mind. It has a Whole extending across two brains and four cortical hemispheres. It sees the world through four eyes, hears through four ears, speaks with two mouths, controls four arms and legs, and shares the personal memories of two lives. (pp. 237-238)
Koch thinks of this as some kind of Über-mind (his term) transcending individual identity. Color me skeptical, very skeptical.
The brain in two worlds
Back there, when we were looking at connecting two cortical hemispheres, you had an objection. I was arguing that there’s no difference between receiving hundreds of thousands of inputs to the visual cortex from the cortex of another brain and hundreds of thousands of inputs from a neuroscientist running an experiment. You were about to point out that, of course, there is a very obvious difference.
Yes, I was, thank you.
And the difference?
Well, the impulses from the brain convey a coherent visual scene while the impulses injected by the scientist could be anything, including noise.
Right. But you must understand that the coherent visual scene coming in from the other brain is not going to arrive as a coherent visual scene. It’s going to arrive as noise.
To understand that we need to think a bit how the brain is structured and constructed. Nothing very deep and complicated.
Let us start with this simple diagram:
It makes a very simple point: that the central nervous system (CNS), with the brain as the largest component, functions in two worlds. There is the external world: the physical world, the world of plants, animals, and other people. And there is the internal milieu: the body’s interior (in which the brain itself is situated). The brain senses the external world through the vision, hearing, smell, taste, touch, and a other senses; it directs action in the world by control of the skeletal muscles. Similarly, it senses the internal milieu through the bloodstream and acts on it through the endocrine system – there is more to it than that, but we don’t need it all; it is the principle that I’m interested in.
This is basically the same diagram, but with just a bit more detail in the central box, the CNS.
Now we have distinct regions for receiving input from the external world (A), from the internal milieu (B), for acting on the internal milieu (C) and for acting in the external world (D). Finally, there is a central area containing neurons connected to neurons in the other areas. While no real nervous system is that simple, they are all elaborations of that basic organization.
And that organization is CLOSED. What do I mean by that?
First, the brain isn’t something that is assembled from a bunch of parts scattered throughout a bunch of bins from which they are fetched by some Transcendental Maker who assembles them into a brain and then flips the ON switch, at which point the brain has guide the body in making its way in the world. No, the brain develops through an organic process that starts with a single fertilized egg which then begins dividing and differentiating. At some point about three weeks into the process specifically neural cells appear in the embryo and then differentiate into the brain and the peripheral nervous system.
The nervous system is far from fully developed at birth, but obviously its operating environment changes drastically at that time. Until that point its external world had been the womb. After birth it is exposed to the larger external world. In humans the brain continues developing into the early twenties, at which time the sutures in the skull finally close completely.
At every point in the process the cells are living cells. The neurons are receiving inputs and generating inputs. They are, in effect, becoming used to one another, “learning” one another’s ways. They are mutually adjusted.
THAT’s what I mean when I say that the system is closed. There is no external meddling going on. How could there be?
External meddling, that is what happens when two brains are hooked together by a high tech coupling (an artificial corpus callosum in Koch’s formulation) linking tens or even hundreds of millions of neurons across two brains. Both brains are now subject to considerable external meddling. Each brain is receiving inputs from a source it has no experience with, and generating outputs to that source as well. As I have indicated before, it has no way of even recognizing the presence of all this foreign input as foreign. It is just there. It is noise, electrochemical energy with no traceable linkage to the organism itself.
I suppose one could imagine that in time, weeks, months, years, the two brains would somehow sort things out. Maybe. But that’s very different from the instantaneous perception and recognition that Koch is talking about. But maybe not. Maybe the initial shock of all that noise is too much to overcome. We simply don’t know.
Bu..bu..but aren’t the two brains alike?
Only approximately, only approximately.
It is easy to identify gross body parts for one individual with the same parts for another. Here’s my left leg, there’s your left leg, here’s my left thumb, there’s your left thumb. But you can’t do that with hairs on the head. For one thing, people don’t even have the exact same number of hairs on their heads.
It is the same with neurons. It is not as though we could link neuron #7,983,004,512 from one brain to neuron #7,983,004,512 in the other brain, and so on for tens or even hundreds of millions of neurons. We have no way of making such identifications between neurons in different brains. Brains are sufficiently different from one another that it is difficult to identify corresponding areas with a high level of precision. Gross correspondence at the scale of centimeters or millimeters is all we can do. That’s not very high precision.
What we have at best, then, is some miraculous technology linking millions or even billions of neurons in one brain with of millions or billions of neurons in another brain in some quasi-ordered pattern based on approximate brain geometry. This technology allows the two brains to send signals to one another, signals which neither brain is prepared to deal with and which therefore interrupt the normal processes of both brains. I do not see how anything resembling coherent thought can emerge from the resulting electrochemical chaos. Even the best of magicians is incapable of pulling a rabbit out of a poorly constructed hat.
Musk doesn’t understand how language works
Now let us turn our attention to Elon Musk. As far as I can judge from the statements that I’ve read and that he has made in various interviews, his conception of brain-to-brain thought transfer is similar to Koch’s, millions of impulses traveling between the two brains in some point-to-point scheme. I see no point on continuing or even elaborating on my critique of Koch.
Rather, I want to take a look at what Musk says about language, for that gives us further insight into the confusion that shrouds this topic. Musk believes that brain-to-brain thought transfer will enable more efficient and accurate communication.
This is what Musk told Tom Urban three years ago :
There are a bunch of concepts in your head that then your brain has to try to compress into this incredibly low data rate called speech or typing. That’s what language is — your brain has executed a compression algorithm on thought, on concept transfer. And then it’s got to listen as well, and decompress what’s coming at it. And this is very lossy as well. So, then when you’re doing the decompression on those, trying to understand, you’re simultaneously trying to model the other person’s mind state to understand where they’re coming from, to recombine in your head what concepts they have in their head that they’re trying to communicate to you. … If you have two brain interfaces, you could actually do an uncompressed direct conceptual communication with another person.
We might represent that process with a diagram like this:
The speaker compresses their thoughts into words. The words travel to the listener who then decompresses them back into thoughts. The process, as Musk states, is not perfect (‘lossy’). What the listener gets out is not quite what the speaker put in.
Unfortunately this account of linguistic communication is wrong. It is an example of what cognitive linguists have termed the conduit metaphor for communication.
In 1979 Michael Reddy published an article based on a group of example sentences . Here are the first three:
- Try to get your thoughts across better
- None of Mary’s feelings came through to me with any clarity
- You still haven’t given me any idea of what you mean
Reddy’s argument is that many of our statements about communication seemed to be based on the notion of sending something (the thought, idea, feeling) through a conduit, hence he calls it the conduit metaphor. Musk embellishes this basic idea with the concept of lossy compression, but that doesn’t over-ride the fact that he talks as though we send language from one person to another through a conduit.
This metaphor implies that meaning is somehow physically IN those words traveling through the conduit. If that were the case then, in a practical sense, there would be no such thing as speech that you cannot understand. You may not know much about quantum mechanics, for example, but if a physicist tells you something about the subject you will understand it immediately. Why? Because the meaning is physically in the words – and in the math symbols. Similarly, someone might tell you a story in Mandarin, a language you’ve never heard – no problem! The story makes perfect sense. Why? Because the meaning is right there in the sounds.
Language doesn’t work like that. Words have two aspects: 1) the signifier (in one standard terminology) is the physical object that is spoken and heard, while 2) the signified is the meaning. It is only the signifiers that physically pass from one person to another in speaking (or writing):
Where does the listener get that signified? They supply it themselves, automatically and without effort. It is always possible that the listener will supply a somewhat different signifier and so get the meaning wrong. Or they may not have a ready meaning available. Or perhaps the speech signal is garbled.
Those are all sources of the ‘lossiness’ that Musk talks about. “Lossiness” may account for a garbled speech signal, but not for the others. They depend on the relationship between signifier and signified. Societies work hard to ensure that words mean the same thing to all people, that is, that the signifieds of all members are mutually coherent, but the process isn’t perfect. In cases where there is a mismatch between speaker and listener, the listener can always ask for clarification: What’d you say? I don’t understand. And so conversations go, back and forth.
Thus to the extent that Musk’s motivation for desiring direct brain-to-brain thought transfer is based on his understanding of linguistic communication, that motivation is deeply mistaken. Yes, it would be nice to improve interpersonal communication, but dreaming about direct brain-to-brain thought transfer is not going to do that.
In any event, even if one were to convince Musk that his conception of language is mistaken – note that I have no experience speaking truth to a billionaire routinely compared to a hero out of the Marvel universe, Tony “Ironman” Stark – I doubt that he would give up his technological quest. Nor should he. At least not for the near- and mid-term medical goals he and his team are pursuing: restoring motor function such as giving people the ability to control artificial limbs, artificial vision, and so forth. Those are considerably more limited than thought transfer, and have been demonstrated in laboratory and clinical settings . Moreover, these technologies require that patients learn how to use them. The nervous system has to adapt to them and assimilate them to its own processes. These are not plug-and-play technologies. But, unlike, brain-to-brain thought transfer, they are real possibilities.
The perils of thinking at the edge of possibility
When Musk, or Koch, or Llinás, or anyone else talks of thinks fondly and longingly about the possibility of direct brain-to-brain thought transfer, they may be using technical language to give form to desire, but that desire is not a grounded in technology. It comes from another source.
Look at the language Koch uses when he talks about the immediate consequences of two minds fusing:
At that moment, your conscious experience of the world vanishes, as does mine. From your and my intrinsic perspective, we cease to exist. But our death coincides with the birth of a new amalgamated or blended mind. (pp. 267-268)
That’s the language of mysticism, not speculative neuroscience. Two paragraphs later he says:
At times, I yearn to fully fuse with my wife’s mind, to experience what she experiences. Sexual union only dimly and transiently achieves this desire—though our bodies are entangled, our two minds retain their separate identities. Mind blending via brain-bridging would allow transcendence, a complete union, an orgasmic dissolution of our distinct identities and the birth of a new soul. (p. 240)
We have left the world of neuroscience, even at its most speculative, and entered the world of a mystic in quest for the technological sublime.
You start by thinking about what technology can do, what it can do now, then a year from now, five years from now, and sooner or later you pass the point where rational discipline is capable of shaping imaginative desire. We are now in “here be dragons” territory. Anything can happen here. Perhaps a friendly dragon, perhaps a monster, perhaps, perhaps… That’s the idea, no?
And yet, for me, journeying to Mars would be more miraculous than brain-to-brain thought transfer. A manned mission to Mars would be an extension of journey’s we have already taken, as flexible and reliable control of artificial limbs would be an extension of technologies demonstrated in laboratories. Neither extension will be easy and straightforward. But they are plausible and should be undertaken.
A journey to Mars would be a great adventure, while brain-to-brain thought transfer is no more than a fond hope. We can go to Mars, though it will be expensive, difficult and dangerous. But there is little chance, no matter how much effort we devote to the project, that direct brain-to-brain communication will ever leave the world of science fiction .
Learning to dream, to translate dreams into rational speculation, those are among the most difficult tasks of all. And the most important.
 Rodolfo Llinás, Wires in the Brain, YouTube video, 2008, https://youtu[dot]be/Pgmoz4f8LA4.
 Christof Koch and Patrick House, Brain Bridging, Nature, 26 August 2010, https://www.nature.com/articles/d41586-020-02469-0.
 Elon Musk’s Neuralink Presentation, CNET Highlights, August 28, 2020, https://youtu[dot]be/sr8hzF3j2fo.
 Elon Musk Reveals New Details About Neuralink, His Brain Implant Technology, JRE Clips, May 7, 2020, https://youtu[dot]be/Gqdo57uky4o.
 The most complete account of Musk’s views that I’m aware of is in a long article by Tim Urban, who had extensive conversations with Musk and members of his Neuralink team. Urban’s article also has a lot of useful information on the brain, but he sticks to the party line on brain-to-brain communication: Tim Urban, Neuralink and the Brain’s Magical Future, Wait But Why, April 17, 2017, https://waitbutwhy.com/2017/04/neuralink.html.
 Christof Koch, The Feeling of Life Itself: Why Consciousness Is Widespread but Can’t Be Computed, The MIT Press, iBooks, 2019.
 Perhaps you are wondering something like this: How do the exogenous spikes coalesce into a coherent thought which thoughts coalescing from endogenous spikes recognize as Other? That’s a good question, one not addressed in accounts of brain-to-brain thought transfer. That’s likely to lead to a discussion of the neural code, which I have addressed in a recent blog post, “The neural code meets Sydney Lamb’s daughter,” New Savanna, September 10, 2020, https://new-savanna.blogspot.com/2020/09/the-neural-code-meets-sydney-lambs.html.
 The Wikipedia article on the conduit metaphor is useful and contains pointers to subsequent research: Conduit metaphor, URL: https://en.wikipedia.org/wiki/Conduit_metaphor. I am working from the second edition of the volume in which Reddy’s article was published: Reddy, Michael J. (1993). The conduit metaphor – a case of frame conflict in our language about language. Metaphor and Thought (2nd edition), ed. Andrew Ortony, 164-201. Cambridge University Press.
 Moises Valasquez-Manoff, The Brain Implants That Could Change Humanity, The New York Times, Aug. 28. 2020, https://tinyurl.com/y6xkjy8z.
 See my recent post for a comparison of the two objectives, “Elon Musk understands the technical challenges of going to Mars, but he’s in the dark about direct brain-to-brain thought transmission,” New Savanna, September 1, 2020, https://new-savanna.blogspot.com/2020/09/elon-musk-understands-technical.html.