This is post 2 of 10 in my sequence on how to sign up for cryonics.

Background

There are currently two options for human cryopreservation: preserving the whole body, or preserving only the brain (and the head that holds it). Note that while cryonics providers Alcor and KrioRus offer both options, the Cryonics Institute only offers whole-body preservation.

This 1995 essay by a former Alcor president does a good job of laying out the considerations that go into this decision. I'll go into many of those as well as some additional considerations in this post. I'm primarily looking at:

1. The practical considerations of preserving a body vs just a brain, including complexity, risk, cost, and preservation quality.
2. The biological and philosophical implications for one's personhood if the body is discarded.

Note that many people argue that it will be easier for whole-body patients to resume their lives and be reintroduced into society – perhaps so much easier that they'll be woken up hundreds of years before neuropatients. I am not going to explore those arguments here because I think it's unlikely that human bodies will be necessary/useful at the time of waking. If you're interested in a discussion of that topic, see Mati Roy's "How much harder is it to revive a neuro-only cryonics patient?"

Arguments for neuropreservation

From Alcor’s FAQ: "Brains are compact, inexpensive to store, easy to move, and are a single organ for which cryopreservation protocols can be completely optimized." That is, if you focus on preserving just the brain, you can do a better job with the initial cryopreservation, and maintain preservation less expensively, and with less risk, for the long years until revival.

Higher-quality preservation

There are reasonable arguments that neurosuspension might result in better preservation than whole-body, and this is a crux for me. However, note that these arguments rest on facts that only happen to be true today. If and when cryonics technology progresses to a point where a person can be preserved indefinitely with no damage whatsoever (some people call this 'true suspended animation'), then this consideration will entirely disappear.

There are many advantages when the perfusion team can exclusively focus on the head, because cryopreservation protocols can be completely optimized for survival of the brain^[1]. Some specific advantages include:

• Shorter perfusion times (sources: 1, 2)
• Faster cooling to temperatures where biological and chemical activity are halted (1)
• Better venous return of the cryoprotectant (2)
• Absence of problems due to abdominal edema
• Potential access to new, more advanced preservation technologies before whole body patients (3)

However, note that you can theoretically get the best of both worlds (emphasis mine):

A rejoinder to this argument is that one does not need to choose neuropreservation to receive these advantages. One could preferentially cryopreserve the isolated head and after this procedure cryopreserve the rest of the body. In fact, as of this writing, the default procedure at the Cryonics Institute is to perform cryoprotective perfusion with a vitrification agent for the upper body and give the rest of the body a straight freeze. At Alcor it is possible to execute a contract that provides for separate cryopreservation of the head and the body. So it is not accurate to say that one needs to exclude the cryopreservation of the body to get a superior cryopreservation. (source)

With Alcor, it’s also possible to get funding for whole-body, but leave a note on your file saying that Alcor can choose the best option based on the circumstances of your demise.

Lower cost relative to whole-body preservation

Assuming you are already set on Alcor (or KrioRus), neuropreservation is substantially cheaper than whole-body preservation – half the price or less. This is primarily (though not solely) because of differing storage costs. Via Alcor:

All of the patients are stored in liquid nitrogen at –320 F [–196 C]. No matter how well insulated, liquid nitrogen is constantly evaporating and returning to the air. We have to add more nitrogen to the dewars each week. Alcor has to pay a local supplier for this liquid. One of our steel Bigfoot dewars boils off about 12-15 liters of nitrogen per day, whether it contains one whole body patient or the maximum of four. Each neurosuspension dewar (inside a concrete vault) holds nine patients and loses nitrogen at only half the rate of the whole-body units. This means the nitrogen cost per neuropatient is only about one-ninth of the cost per whole-body patient.^[2]

There are many other factors in the storage costs that are more evenly divided between neuro and whole-body patients, so the total difference is not 1/9; but it is still large. To ensure enough principal in the Patient Care Fund so that the earnings can cover expenses, we invest $70,000 (at least) of the suspension funding for whole body patients. We only have to invest about $17,000 to achieve the same result for neuropatients.

Neuropreservation may also be less subject to cost increases than whole-body. This is an impression I've gotten from multiple sources but haven't seen a very explicit model for. One suggestion is that whole-body has more room for cost increases due to technological innovation, because body perfusion and preservation is less advanced and less explored than brain preservation. I've also seen claims that Alcor whole-body preservation is currently underpriced.

Emergency evacuation

Again, via Alcor:

Neuropatients are also easier to transport in an emergency. The Bigfoot units are about nine feet tall, weigh almost 2 1/2 tons, and take several people to move. However, we can quickly move the neuropatients to small, individual dewars that can be placed in the back of a van or pickup truck and handled easily by two people.

In a major emergency, Alcor would convert whole body patients to neuropatients, and evacuate them in the same way. However, this would take extra time, decreasing your odds of survival. 

While emergency transportation has rarely come up so far in cryonics history, it's not a stretch to imagine that, over timescales of a hundred years or more, a natural disaster might threaten the facility where you're being stored.

Arguments for whole-body preservation

See The Case for Whole-Body if you want someone to do their best to convince you to sign up for whole-body; I'm here to explain, not persuade.

Lower cost in absolute terms

If you are price-sensitive above all else, you're likely to choose the Cryonics Institute for your cryopreservation (more on this decision in the next post), since it charges $28,000 for whole-body suspension^[3], compared to Alcor's $80,000 neurosuspension or $200,000 whole-body suspension. Since the Cryonics Institute only offers whole-body preservation, making your decision based primarily on price de facto means choosing whole-body.

Compensating for damage to the preserved brain

From The Case for Whole-Body: 

If we... allow for some degree of ischemia or brain damage during cryopreservation... the rest of the body could be used to infer information about the non-damaged state of the brain, an option not available to neuropatients.

Recently, research has been conducted to understand the “microbiome” and the alleged interaction between gut bacteria and the brain. One does not need to believe that the microbiome is part of the (peripheral) nervous system to recognize that its preservation (and gut bacteria in particular) may provide clues about the brain, (past) mental states, and could be useful to resolve ambiguous brain repair challenges.

The essay doesn't specify how any of this might work, but then again, we by necessity never specify how revival might work beyond "advanced nanomedicine." The claim seems a priori plausible to me.

Potential cognition outside of the brain

From The Neuropreservation Option:

Certainly a whole body patient takes more total information along into the future, although it is still hard to say how significant the added information is. For some people, the pattern of nerve growth development in the body may be very important to their identity — for a dancer or musician, for instance. On the other hand, enough of that information may be encoded in brain development that the same result can be achieved either way. We don’t know yet; so we can’t say for sure if you are risking anything by leaving your body behind.

This feels like a crux for me, so I want to drill down into it – it seems to me that the bulk of the considerations point in favor of neuropreservation (given current technology), but if it's true that by choosing neuro I'd be leaving important parts of myself behind, that would tip the scales in favor of whole-body for me.

While there's definitely uncertainty here that hasn't been resolved by contemporary science, we can at least bring some evidence to bear. Fortuitously, I found out that my friend Eli had already done a little bit of research and thinking in this area, and he agreed to let me use his work. The next three sections were almost entirely written and researched by him, with only some minor edits by me.

Does important cognition happen outside of the brain?

Note from Eli: I did spend a couple of hours trying to follow up on evidence related to this question, but I definitely definitely don’t feel like I solidly “figured it out”. The following is more like a survey of the evidence that I happened to find. I do think there is space for a person to do a more dedicated research project here (on the order of 30 or 40 hours), and get more clarity.

Background

Proponents of whole-body preservation suggest that important personality-relevant information is stored in the rest of the body, not just the brain, and suggest that it might be shortsighted to not preserve that information.

From my layman’s understanding, this is at least plausible: the body is composed of multiple overlapping systems, such as the endocrine system, the immune system, the peripheral nervous system, and the enteric nervous system, each of which has some function analogous to memory, and which interact with each other in complex cascades. (Not to mention almost all the cells, in all the tissues in your body, which adaptively adjust the mix of receptors on their membranes, depending on the chemical soup that those cells are exposed to.)

Therefore it wouldn’t be that surprising to me (again, as a layman) if, when you isolate the brain from all of those systems, you are leaving behind an important fraction of a patient’s personhood.

Which option is preferable depends on a number of factors, but surely one major crux is “How much personality-relevant information is stored in organs or organ systems other than the brain?” This is a tricky question to answer for a number of reasons, both scientific and philosophical. I want to investigate the easiest line of attack I can think of: “Do paraplegics experience personality changes as a result of their spinal trauma?” 

This seems like the easiest line of attack, because the spine is an organ outside of the brain, that we know has the capacity for learning, and which has a pretty well-defined channel of interaction with the brain.

If we find that paraplegics do suffer (permanent) personality changes, that would be pretty significant evidence that personality-relevant information is contained in the rest of the body, even if it is only in the spine.

If we find no evidence of personality change in paraplegics, that would be some evidence in favor of most or all of the important personality-relevant info being in the brain, but it would hardly be conclusive, since there are a bunch of other systems that could constitute an important, idiosyncratic part of “personhood.”

Nevertheless, this seems like the best place to start. So, I did a lit review to see what I could find on the topic.

Evidence from spinal trauma patients

I struggled to find evidence relevant to this question.

The first problem is that while there are a number of papers about personality disorders in spinal cord injury (SCI) patients, they seem to be due to selection effects – for instance, aggressive, impulsive risk-takers are far more likely to be involved in activities that might result in a SCI. I have yet to find any studies that do a before and after analysis on a person who suffered from a spinal cord injury. One paper got close to that by comparing the personality assessment of veterans with SCI, to the personality assessment of their identical twins. They found “no evidence that SCI is associated with long-term personality change.” But also, the sample size was only 11 pairs of twins.

The second problem is that paraplegics' lives change radically following their injury. To get proper evidence, we would need to distinguish between personality changes that are the result of their change in circumstances, vs personality change that is a direct result of physical trauma.

Biological mechanisms of personality change

Since the evidence from SCI patients was so scarce, I decided to switch to looking into our models of how personality change via brain damage happens. Here is some of what I found.

“Personality changes” primarily refer to changes in the emotional responses to stimulus. Most often this seems to take the form of disimprovement in emotional regulation: increased irritability, anger, or frustration, and decreased impulse control. For instance, take the famous case of Phineas Gage, who had a railroad spike driven through his frontal lobe in an accident:

Gage’s employers... “considered the change in his mind so marked that they could not give him his place again.... He is fitful, irreverent,... impatient of restraint or advice when it conflicts with his desires.... His mind was radically changed, so decidedly that his friends and acquaintances said he was ‘no longer Gage.’” (source)

However, sometimes affective reactions shift in less predictable ways. For instance, brain injury victim Oliver Mitchard reports:

Before my accident, I wasn’t fond of animals or monkeys - no creatures at all. Since my accident I’ve got a massive passion for monkeys, which bizarrely, has literally come out of nowhere.

It seems like the best theory to describe this is that when the connections between the limbic system and the cerebral cortex are damaged, and forced to regrow, this can cause changes to the patterns that allow us to evaluate our emotional responses and regulate our behavior. (Note from mingyuan: while the sources I could find on this are not exactly the height of scientific legitimacy, it still seems plausible to me.) 

That is, personality changes are attributed to the brain alone, with no involvement from the central or enteric nervous systems. Any personality changes due to spinal or abdominal trauma would need to posit a totally new biological mechanism.

Eli's part is over now, back to me.

Other evidence

Former Alcor president Mike Darwin commented on this issue back in 2012, focusing on several examples not covered by Eli:

First, Darwin points out that there are major personality changes and other cognitive changes entailed in aging, and we generally don't think of these as compromising a person's self. (Think aging as in age 25 to age 35, rather than aging as in dementia.) I think this is pretty uncontroversial – I certainly have different emotional reactions to stimuli than I would have 10 years ago, but nobody questions my continuity of consciousness.

Second, he claims that he knows plenty of people who have had their intestines and stomach (where many extra neurons are located) removed, but didn't undergo any perceptible cognitive changes.

I actually found a ton of anecdotal evidence that stomach surgery can lead to significant personality change. But again, it's hard to separate effects of the surgery itself from everything that surrounds it. Losing 100+ pounds will have massive effects on your social and mental life whether it involves surgery or not, as will being diagnosed with gastric cancer (weight loss and cancer are the two reasons people get stomach surgery). You also have to make permanent, significant changes to your eating behaviors after stomach surgery, which can affect all sorts of things (e.g. blood sugar and hormone levels, habits and coping mechanisms, general enjoyment of life).

Finally, Darwin points out that in successful organ transplants, donor immune and stem cells colonize the patient, but the patients don't undergo perceptible cognitive changes – despite the fact that the makeup of their 'chemical soup' (to use Eli's phrase) has changed significantly.

A quick search on my part turned up a couple papers and plenty of anecdotes suggesting that a small subset of organ recipients do report personality changes that they attribute to their transplant. While that seems plausible to me a priori, I'm distinctly unimpressed with the research – there's no proposed mechanism and it all feels more spiritual than scientific. (Search term: 'cellular memory theory'.)

Oh no, philosophy

It turns out that the fact that personal identity is poorly defined makes it really hard to say what information is identity-relevant, and therefore it's hard to decide whether your brain in isolation would still be you. I think we're running into something like a Ship of Theseus problem here – how many pieces of what makes me me can be taken away before I'm no longer me?

Another way to look at it is that personalities are already dynamic, and so it becomes a matter of personal judgment what kinds of personality changes are within acceptable limits, and which are not. Some dimensions on which personality changes appear to vary are:

• Magnitude – It's easier to accept small changes than large ones. The changes in Phineas Gage were very large, but if someone ended up only 5% more irritable or impulsive after an accident, you might not even notice.
• Abruptness – It's easier to accept gradual changes than abrupt ones. You undergo gradual changes in personality as you age. You can get abrupt changes if you experience a traumatic brain injury.
• Externalness – It's easier to accept internal changes than external ones. An organ transplant or a rod through the head are clearly external. Meditating is clearly internal. Taking antidepressants or hanging out with new friends are borderline.
• Type – It's easier to accept positive or neutral changes than negative ones. Contrast Phineas Gage's aggression and impulsiveness to Oliver Mitchard's newfound passion for monkeys.

Mati suggests thinking in terms of "the things you intrinsically want to preserve about yourself" – which again, is a matter of personal judgment. The only thing I can really pin down is that I want continuity of consciousness – I want to keep my memories and my sense of being myself. But surely I wouldn't be satisfied with a person with all of my memories, but who reacted differently from me to every conceivable stimulus. In short, this is all very confusing, oh no.

Conclusions

Eli's conclusion

This is non academic, but I can say that as I continued looking into this, I found an increasing inclination to cryopreserve my whole body. Importantly, the update was not that there’s strong evidence to think that personality-relevant information is stored in the brain, but rather, it was (re-)made salient to me how little we know about how brains and minds work. 

Given how little we know, it seems like epistemic arrogance to confidently assert that (and bet on) there being negligible biological personality-relevant info outside of the brain. The precautionary principle argues in favor of not leaning on that fact for “my” survival. 

ETA: It seems worth noting that I have opted for neuropreservation instead of full body, at least at this time, in large part due to price difference. The "inclination to cryopreserve my full body" noted above, was not sufficient to sway my choice. What seems ideal to me would be doing both: remove the head from the body, and then cryopreserve, and store, them both separately. This would give you the benefit of a faster perfusion of the brain and ease of transport in an emergency, but also keeps the rest of the body around on the off-chance that it contains personality-relevant info.

My conclusion

Every line of inquiry so far has failed to suggest that any important aspects of personality are located anywhere except the brain. Absence of evidence is (weak) evidence of absence – especially given that this is not the first time I've been in a context where I needed to know whether anything other than the brain was important for identity and cognition. 

Given that the bulk of the considerations – cost, emergency risk, and most importantly, preservation quality – are in favor of neuropreservation, and I haven't seen any compelling reason to switch to favoring whole-body, I am choosing neuropreservation for myself and my family members. It seems to me that, as of this writing, neuro gives the best chance for future revival.

However, I think it's quite likely that cryopreservation technology will advance enough in my lifetime that it will at some point make sense to switch to whole-body. So I recommend signing up for neuropreservation, but with a high enough funding amount that you can easily switch to whole-body in the future without needing to purchase additional life insurance. More on this when I cover life insurance in two weeks.

1. ^{^}

   "The quality of brain preservation in whole body patients may not be as good as for neuropatients. Cryoprotectant absorption of the entire body is measured during whole body cryopreservation. During neuropreservation, cryoprotectant absorption of each brain hemisphere is individually measured and optimized without interference from the rest of the body." (source)

2. ^{^}

   This calculation appears to assume that whole-body dewars store an average of two patients rather than the maximum of four. I'm not sure why this is.

3. ^{^}

   The $28,000 figure is somewhat misleading, as I'll discuss in depth next week.