In the 1970s the United States and United Kingdom began to institute new laws governing the determination of death. To the traditional criterion of respiratory/circulatory failure, the United States added an alternative criterion: death of the entire brain, including the brainstem. In the United Kingdom, the death of the brainstem alone was considered sufficient. The U.S. definition is sometimes called “whole-brain death,” while the U.K. one is known as “brainstem death.”
The brainstem is critical for both respiration and consciousness. Its neurons generate signals that control the breathing muscles. If they fall inactive, breathing stops, and the patient cannot live without a mechanical ventilator. It is the brainstem’s role in breathing that gives brainstem death its close tie to the traditional notion of respiratory/circulatory death. Another role played by the brainstem, perhaps even more important, is that it arouses the rest of the brain to consciousness. Our level of arousal goes up and down all the time, most dramatically in the sleep–wake cycle. Several populations of brainstem neurons, collectively called the reticular activating system, send their axons widely over the brain. These neurons secrete special neurotransmitters known as neuromodulators, chemicals that “wake up” the thalamus and cerebral cortex. Without them the patient cannot be conscious, even if the rest of the brain is intact.
The situation can be summarized this way: “If the brainstem is dead, then the brain is dead, and if the brain is dead, the person is dead.” That’s the rationale for the U.K. notion of brainstem death, and it makes sense because the brainstem typically functions longer than any other part of the brain. Damage to the brain causes cerebral edema, an abnormal buildup of fluid. This raises the pressure in the skull, causing blood flow to stagnate. Even more cells die, causing more edema and further shutting down the blood flow. The vicious cycle continues, and culminates with the brainstem being crushed by the pressure. So if the brainstem no longer functions, it’s likely that the rest of the brain has already been destroyed.
This is the normal course of events. But sometimes—rarely—the entire brainstem is destroyed while the rest of the brain is left intact. The patient will never breathe without a mechanical ventilator, and will never regain consciousness. Yet one could argue that the patient still lives, assuming that memories, personality, and intelligence are preserved in the cerebrum. These properties seem more fundamental to personal identity than respiration, circulation, or brainstem function.
Today this distinction is merely theoretical, because no patient with complete brainstem damage has ever regained consciousness. But imagine a future medicine in which physicians can induce neurons in the brainstem to regenerate, reversing the damage. Then it might be possible for the patient to become conscious and functional again. The idea that the failure of the brainstem means that the person has died could eventually seem as outmoded as considering someone dead after respiratory/circulatory failure that is reversible.
Such future developments may seem far-fetched, but prognostication is not the real goal here. Rather, these thought experiments should motivate us to find a definition of death that is more fundamental. Ideally, the definition should remain valid no matter how far medicine progresses in the future. In this book I’ve talked about various ways of testing the hypothesis “You are your connectome.” If this hypothesis is true, a fundamental definition of death follows immediately: Death is the destruction of the connectome. Of course, we don’t know yet whether a connectome contains a person’s memories, personality, or intellect. Testing these ideas will occupy neuroscientists for a very long time.
In the near term, all we can do is speculate. It’s possible that a connectome contains most of the information in a person’s memories. But even if that’s the case, a connectome might not contain all of the information. Like any kind of summary, a connectome leaves out some details. Some of that discarded information could be relevant to personal identity. I conjecture that connectome death implies loss of a person’s memories. However, the converse may not be true. Some of the information in a person’s memories might be lost even if the connectome is perfectly preserved. (I’ll tackle the issue of completeness in the next chapter.)
In its emphasis on brain structure, connectome death departs from conventional definitions based on brain function. The legal definition of death is the irreversible loss of function of the whole brain or of the brainstem. But as we’ve seen, the term irreversible is problematic. Snakebites and certain drugs can mimic brainstem death, but this loss of function is reversible. After mechanical ventilation for a short period, the patient recovers completely. So even for an expert, it can be tricky to decide when loss of function is permanent.
On the other hand, connectome death is based on a structural criterion that implies a truly irreversible loss of function (assuming that it implies the loss of memories). Alas, this definition is practically useless in a hospital. Currently, in live patients we can measure brain function through reflexes mediated by the brainstem, brain waves (EEG), or functional MRI. But we know of no way to find neuronal connectomes of living brains.
I can think of only one practical application of the idea of connectome death. Perhaps it’s not really that practical, but I find it fascinating nonetheless. Why not use connectomics to critically examine the claims of cryonics? I’ve described at length the ways in which the brains of Alcor members have been damaged by circulatory/respiratory death and vitrification. Is there any chance that this damage could be reversed, as Alcor claims? To find out, I propose that we attempt to find the connectome of a vitrified brain. If the information in the connectome turns out to be erased, then we can declare connectome death. Resurrection by an advanced civilization of the future might be possible, but only for the body, not for the mind. If, however, the information is still intact, then we cannot rule out the possibility of resurrecting memories and restoring personal identity.
I suppose we should not conduct this experiment on a vitrified human brain. But Alcor has also vitrified the brains of some dogs and cats, at the request of pet-loving members. Perhaps some of these members would be willing to sacrifice their pets’ brains in the name of science?
Until this scientific test is conducted, we can only speculate about what it might find. It’s well-known that the brain is extremely sensitive to oxygen deprivation. Loss of consciousness follows in seconds, permanent brain damage after a few minutes. This is why disruption of blood flow to the brain can be so deadly, as happens in a stroke. At first glance, this seems like bad news for Alcor members. By the time Alcor receives the corpse, the brain has been deprived of oxygen for hours at least, and no living cells may remain. (Of course, it can be as difficult to define life and death for a cell as for the whole body.) Whether dead or alive, the cells have been badly damaged. Electron microscope (EM) studies have characterized the types of damage present in brain tissue a few hours after respiratory/circulatory death. Among other changes, mitochondria look damaged, and the DNA in the nucleus is abnormally clumped.
But these and other cellular abnormalities are irrelevant for connectome death. What matters is the integrity of synapses and “wires.” Synapses seem less of a problem; they are still intact in the EM images, so they appear to be stable even in a dead brain. The status of axons and dendrites is harder to judge. Their cross-sections look largely intact in the published two-dimensional images, but there are some damaged locations. The big question is whether the damage has actually broken the “wires” of the brain. This can be answered by attempting to trace the neurites in three-dimensional images. If there are few breaks, tracing might still be possible. One could deal with an isolated break by bridging the gap between two free ends that were obviously once joined. But if there are clusters of many adjacent breaks, it might be impossible to figure out which free ends were once joined together. This would be true connectome death, a loss of information about connectivity that can never be recovered, no matter how advanced the technology.
At the present time, c
ryonics is closer to religion than to science, because it is based on faith rather than evidence. Its members believe that a future civilization will be able to resurrect them, based only on their faith in limitless technological progress. The test that I propose is a way of finally bringing some science to Ettinger’s Wager. If the vitrified bodies contain intact connectomes, this does not prove that resurrection will be possible. But if connectome death has already occurred, resurrection will almost certainly be impossible.
Many Alcor members might not be eager to see the results of such a test. They may prefer blind belief as a means of consolation about their impending demise. If a scientific test has the potential to uncover factual information refuting their beliefs, they might prefer that the test not be conducted. There may be other members, though, who want evidence over faith, and would demand tests of connectome integrity.
It could turn out that the Alcor members stored in liquid nitrogen are already connectome dead. If so, that would not be the end of Alcor. They could always use connectomics as a means to improve their methods of preparing and vitrifying brains. Short of actually resurrecting their members, this is the only way I can imagine assessing the quality of their procedures. Even if their current method does not prevent connectome death, they could ultimately find one that does.
Cryonics is not the only way to preserve a body or a brain for the future. In his 1986 nanotechnology manifesto, Engines of Creation, Eric Drexler proposed that brains be preserved by chemical means. In a 1988 paper modestly titled “A Possible Cure for Death,” Charles Olson independently proposed the same thing.
What Drexler and Olson were proposing was not a new procedure, but a new use for an old procedure called plastination. You may have seen one of the popular traveling exhibitions of human bodies preserved in plastic. Similar methods have long been used to prepare tissue for electron microscopy. The goal goes beyond merely preserving the look of tissue to the naked eye. Researchers try to leave every cellular detail intact, down to the structure of individual synapses. First, special chemicals like formaldehyde are delivered to cells by circulating them through the blood vessels. These are called fixatives, because they create links between the molecules that make up cells, fixing them in place. Once reinforced in this way, cellular structures are protected from disintegration. Then the water in the brain is replaced by alcohol, which in turn is replaced by an epoxy resin that hardens in an oven. The final product is a plastic block containing brain tissue (see Figure 53, left). The block is hard enough that it can be cut thinly with a diamond knife, as we do when finding connectomes.
Figure 53. Plastination: brain tissue preserved in epoxy (left) and insect in amber (right)
Aldehdye fixation, the first step of plastination, is also used by morticians when preserving bodies. This practice is called embalming, and is used to prepare bodies for temporary public display at funerals. In rare cases, the public display doesn’t end with the funeral. For example, the Russian revolutionary Vladimir Lenin was embalmed after his death in 1924, and his body can still be seen in a Moscow mausoleum. It’s not clear how long an embalmed body will remain intact. And even if it appears normal, its microscopic structure may be deteriorating. The full plastination procedure preserves biological structures indefinitely. The result looks similar to insects trapped in fossilized amber (Figure 53, right), some of which are millions of years old.
Plastination could be safer than cryonics, because it does not depend on a constant supply of liquid nitrogen. If Alcor goes bankrupt, or some kind of disaster damages its warehouse, the bodies and brains would be jeopardized. But a plastinated brain requires no special maintenance. Charles Olson predicted that “the cost of brain chemopreservation could be less than that of a typical funeral.” There is an important stumbling block, though: Right now, plastination works on only very small pieces of brain. For various technical reasons, no one has yet succeeded in preserving an entire human brain with its connectome intact.
Ken Hayworth recently decided to do something about this. As you’ll recall, he invented ATUM, the machine that slices brains thinly and collects them on a plastic tape for imaging and analysis. Many neuroscientists are driven not only by curiosity but also by ambition. Some want to discover something about the brain that will yield their next publication or promotion. Others aspire to win a Nobel Prize. But Hayworth makes all their ambitions look pedestrian. His goal is to live forever. As Woody Allen said, “I don’t want to achieve immortality through my work. I want to achieve it through not dying.”
Hayworth and his colleagues have established the Brain Preservation Prize, which offers $100,000 to any team that can successfully preserve a large brain in a way that leaves the connectome completely intact. A quarter of the prize money can be won by preserving a mouse brain. This is regarded as a steppingstone to a human brain, which is a thousand times larger in volume.
Hayworth is planning to plastinate his own brain. He would like to do this well before he dies of natural causes, while his brain is perfectly healthy. That would best preserve his brain for the future, but, by any ordinary definition, it would also kill him. He may have difficulty finding helpers, because their acts would likely be regarded as assisted suicide. Hayworth argues that plastinating his brain would not be suicide but salvation. It’s his only chance at eternal life.
But how do you revive a plastinated brain? Raising the temperature brings cryopreserved sperm back to life. One can imagine thawing the bodies in the Alcor warehouse, but reversing aldehyde fixation and epoxy embedding seems much more difficult. Then again, if a civilization of the future is advanced enough to resurrect the dead, maybe they will also be advanced enough to unplastinate them. Eric Drexler imagined that an army of “nanobots,” robots as tiny as molecules, might be used to unplastinate bodies and brains and repair whatever damage they’ve suffered. In the twenty-five years since then, nanotechnology does not seem to have moved any closer to realizing his dream.
Hayworth has thought carefully about his plans. If his plastinated brain cannot be revived, there might be an even better alternative. He imagines a future version of his ATUM invention, scaled up to handle a large brain—his brain. Once cut into ultrathin slices, his brain will be imaged and analyzed to find his connectome. The information will be used to create a computer simulation of Hayworth, one that thinks and feels like the real thing. This plan seems even more far-fetched than cryonics. Could it really be feasible?
15. Save As . . .
It’s distressing how little they tell us about heaven. We can at least imagine the gates. They are pearly and perched on a cloud. Saint Peter stands guard, ready to make sinners sweat by posing tough questions. But what is it like inside the gates? Everyone wears white. (I’m not sure how I feel about that.) The harp is the only accessory, and angels abound. These snippets of information aren’t much to go on. Only recently did I realize why religions might prefer to be vague: People would rather fantasize about their own heaven than have one thrust upon them.
In the world’s cultures and religions, conceptions of heaven have evolved slowly throughout history. Late in the second millennium, a radically new one emerged:
Heaven is a really powerful computer.
I don’t mean that ecstatic look some nerds get when fondling their laptops. Let’s not mistake such fetishism for a sign of spiritual enlightenment. But then again, why do these people spend so many of their waking hours online? Would it be too far-fetched to say that they thirst for transcendence, that they yearn to escape the inadequacies of this body and this world? While online, teenagers can forget the embarrassment of their pimply faces and underdeveloped physiques. People can take a pseudonym, alter their age, or masquerade with a photo of their dog. Netizens are free to be who they want to be, rather than who they really are.
A body chained to a computer, glassy eyes staring at a glowing screen, and fingers pecking away on a keyboard. That’s a slightly less corporeal existence, to be sure, but I would only call it
purgatory. It’s still not what I mean by the new idea of heaven. Some nerds want more. They would like to discard their bodies completely and transfer their minds to computers. The idea of living as a computer simulation has been embraced by science fiction, which calls it “mind uploading,” or “uploading” for short.
It’s not possible yet, but perhaps all we have to do is wait for computers to get more powerful. Video games are stunning proof that computers can simulate the physical world. Every year the scenery looks more detailed and lush; every year bodies move in more lifelike ways. If computers can do that, why can’t they simulate minds?
It’s no exaggeration to compare uploading with ascension to heaven. Just think about the word itself. “Uploading” gets the direction right, as most agree that heaven is located in a high place. Some devotees prefer to say “mind downloading,” but they are in the minority. It’s not hard to understand why—“downloading” sounds suspiciously like going to hell.
Like thoughts of a traditional heaven, belief in uploading helps us cope with fear of death. Once uploaded, we would become immortal. But that’s just the beginning. In the virtual world, we could beautify and strengthen our bodies simply by reprogramming the computer simulation. No need to suffer at the health club. Or perhaps we’ll rise above such superficial concerns and focus instead on improving our minds. Let’s not just upload—let’s upgrade!
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