I woke up on Saturday to a heartbreaking front-page article in the New York Times about a terminally ill young woman who chooses to freeze her brain. She is drawn into a cottage industry spurred by “transhumanist” principles that offers to preserve people in liquid nitrogen immediately after death and store their bodies (or at least their heads) in hopes that they can be reanimated or digitally replicated in a technologically advanced future.
Proponents have added a patina of scientific plausibility to this idea by citing the promise of new technologies in neuroscience, particularly recent work in “connectomics”—a field that maps the connections between neurons. The suggestion is that a detailed map of neural connections could be enough to restore a person’s mind, memories, and personality by uploading it into a computer simulation.
Science tells us that a map of connections is not sufficient to simulate, let alone replicate, a nervous system, and that there are enormous barriers to achieving immortality in silico. First, what information is required to replicate a human mind? Second, do current or foreseeable freezing methods preserve the necessary information, and how will this information be recovered? Third, and most confounding to our intuition, would a simulation really be “you”?
I study a small roundworm, Caenorhabditis elegans, which is by far the best-described animal in all of biology. We know all of its genes and all of its cells (a little over 1,000). We know the identity and complete synaptic connectivity of its 302 neurons, and we have known it for 30 years.
If we could “upload” or roughly simulate any brain, it should be that of C. elegans. Yet even with the full connectome in hand, a static model of this network of connections lacks most of the information necessary to simulate the mind of the worm. In short, brain activity cannot be inferred from synaptic neuroanatomy.
Synapses are the physical contacts between neurons where a special form of chemoelectric signaling—neurotransmission—occurs, and they come in many varieties. They are complex molecular machines made of thousands of proteins and specialized lipid structures. It is the precise molecular composition of synapses and the membranes they are embedded in that confers their properties. The presence or absence of a synapse, which is all that current connectomics methods tell us, suggests that a possible functional relationship between two neurons exists, but little or nothing about the nature of this relationship—precisely what you need to know to simulate it.
Additionally, neurons and other cells in the brain are in constant communication through signaling pathways that do not act through synapses. Many of the signals that regulate fundamental behaviors such as eating, sleeping, mood, mating, and social bonding are mediated by chemical cues acting through networks that are invisible to us anatomically. We know that the same set of synaptic connections can function very differently depending on what mix of these signals is present at a given time. These issues highlight an important distinction: the colossally hard problem of simulating any brain as opposed to the stupendously more difficult task of replicating a particular brain, which is required for the promised personal immortality of uploading.
The features of your neurons (and other cells) and synapses that make you “you” are not generic. The vast array of subtle chemical modifications, states of gene regulation, and subcellular distributions of molecular complexes are all part of the dynamic flux of a living brain. These things are not details that average out in a large nervous system; rather, they are the very things that engrams (the physical constituents of memories) are made of.
While it might be theoretically possible to preserve these features in dead tissue, that certainly is not happening now. The technology to do so, let alone the ability to read this information back out of such a specimen, does not yet exist even in principle. It is this purposeful conflation of what is theoretically conceivable with what is ever practically possible that exploits people’s vulnerability.
Finally, would an upload really be you? This is unanswerable, but we can dip our toes in. Whatever our subjective sense of self is, let’s assume it arises from the operation of the physical matter of the brain. We could also tentatively conclude that such awareness is substrate-neutral: if brains can be conscious, a computer program that does everything a brain does should be conscious, too. If one is also willing to imagine arbitrarily complex technology, then we can also think about simulating a brain down to the synaptic or molecular or (why not?) atomic or quantum level.
But what is this replica? Is it subjectively “you” or is it a new, separate being? The idea that you can be conscious in two places at the same time defies our intuition. Parsimony suggests that replication will result in two different conscious entities. Simulation, if it were to occur, would result in a new person who is like you but whose conscious experience you don’t have access to.
That means that any suggestion that you can come back to life is simply snake oil. Transhumanists have responses to these issues. In my experience, they consist of alternating demands that we trust our intuition about nonexistent technology (uploading could work) but deny our intuition about consciousness (it would not be me).
No one who has experienced the disbelief of losing a loved one can help but sympathize with someone who pays $80,000 to freeze their brain. But reanimation or simulation is an abjectly false hope that is beyond the promise of technology and is certainly impossible with the frozen, dead tissue offered by the “cryonics” industry. Those who profit from this hope deserve our anger and contempt.
Michael Hendricks is a neuroscientist and assistant professor of biology at McGill University.
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