Summary

In brain information preservation, an important question is the extent to which one should optimize for the conservation of physical states in (a) the brain or (b) the whole body including the brain. A relevant parameter is attempting to preserve traits as opposed to states. The fundamental claim of brain preservation is that adequately conserving the brain alone would be enough to retain the information for long-term memories and core personality traits, because it is the only part of the body that is known to be irreplaceable without massive effects on this information. There is a spectrum of possible procedures that each privilege the brain to a different degree, each with their own upsides and downsides. My personal view is that preserving the brain alone should be the focus because it has clear value and is a difficult enough problem. Others may feel that the rest of the body is irreplaceable or that preserving the brain is not such a difficult task, in which case they may want to focus on preserving the rest of the body as well.

The embodied and embedded brain

Even for a materialist who thinks that the brain is sufficient to produce a mind, it does not make sense to speak of human brain function without considering the function of the rest of one’s body. They are completely intertwined.

In other words, the brain is “embodied.” Here we are using the word “embodied” in the sense of “include or contain something as a constituent part.” The brain functions in large part to make predictions about the world and then produce actions in behavior-sensation feedback loops with the rest of one’s body.

Similarly, the embodied nature of our brains goes beyond this to our “embedded” relationship with the environment. Humans are organisms that exist in a contextualized environment with other humans, other animals, objects, places, and natural phenomena. Our dependence on other people, other organisms, and objects in the external world has been called the “extended mind”.

A friend once asked me whether after the theoretical revival from brain preservation, the idea is that someone would “live in an iPod or something.” Generally speaking, the answer is definitely not. Without the rest of one’s body and an appropriate environmental context, it’s hard to conceptualize how a person’s brain could function anywhere close to optimally.

Instead, the idea is that the rest of one’s body and environmental context are replaceable. The rest of one’s body is necessary in the same sense that legs are necessary to walk but can be replaced. Whereas, in the way that many people think about it, the brain is not: their brain is who they are. Basic neuroscience teaches us that your brain controls your memories and personality traits such as thinking, planning, judgment, and emotions (Stangor et al., 2014). So while a successful revival must involve the non-brain parts of the body and an environmental context for the person, it doesn’t need to be the original non-brain parts and the original environmental context. These could be replaced, synthesized, and/or simulated.

States and traits

In order to address this question in more depth, it’s helpful to consider the concept of a psychological state vs trait (Kraemer et al., 1994).

States tend to be short-term. They are endogenous (e.g. hormonal) or exogenous (e.g. environmental) sources of variation within individuals. If one is in the midst of a major depressive episode, that’s a state. If someone just smoked cannabis, that’s also a state.

Traits, on the other hand, are long-lived and stable across contexts. They refer to long-term personality styles, such as shyness, honesty, or curiosity.

Cicero made the state vs trait distinction in 45 BCE: “It is one thing to be irascible, quite another thing to be angry, just as an anxious temper is different from feeling anxiety. Not all men who are sometimes anxious are of an anxious temperament, nor are those who have an anxious temperament always feeling anxious.” (Chaplin et al., 1988).

From the perspective of preservation metrics, our focus is on long-term traits as opposed to short-term states. States are transient and are not generally valued in the same way. States are also less robust and more difficult to preserve. Let’s examine a few examples of state vs trait reasoning to flesh it out a bit.

Tyler Cowen once noted that he thought cryonics had a low chance of working in part because of the impact of hormones from non-brain areas, such as the gut, affecting one’s brain and mental states. But generally speaking, gut-brain interactions would affect states, not traits. We likely wouldn’t say that someone’s core traits and personhood would be lost if their gut-brain interactions were altered. Otherwise, fecal microbiota transplants might be thought of as killing someone and creating a new person.

A similar discussion could be had about altered levels of thyroid hormones. If someone’s thyroid stops producing thyroid hormone, they frequently develop depression, memory problems, or other changes to their mental states. When thyroid function is replaced by medications, it can dramatically affect their mental states. And yet, people don’t tend to worry about their identity changing upon replacing thyroid function. On some deep philosophical level, given certain assumptions about personal identity, maybe they should. But most people don’t. It is in this every-day sense of “let’s just replace the thyroid function so I get back to normal and feel like myself again,” similar to the concept of ordinary survival, that states are not a priority to preserve.

Long-lasting states

There’s a wrinkle here in that some aspects of someone’s experience could be life long, and yet they might still consider this aspect of their functioning a state as opposed to a trait. To me, this is an area of uncertainty. Perhaps the key question is whether the state can be easily reversed.

An example of a long-lasting state, as discussed by Mike Darwin, is hereditary hyperinsulinemia caused by disordered pancreatic function. If someone is born with a mild hyperinsulinism, it’s possible that they could become irritable when they become hypoglycemic, especially if they have had a longer than normal period of fasting. This propensity towards irritability might even seem like a somewhat important aspect of their personality, at least from an outsider’s perspective. If the person had a new body upon theoretical revival, the degree of hyperinsulinism might not be matched, either because it was hard to ascertain or because of the person’s preference. Either way, this might lead to a change in that person’s personality, wherein one might become less irritable when hypoglycemic.

My guess is that for most people, a theoretic revival procedure involving a new pancreas would not cause them to feel that their fundamental identity had changed. In the same way that they probably wouldn’t feel their identity had changed if they started taking the medication diazoxide to treat their hyperinsulism. Instead, this would likely be seen as a welcome quality of life improvement. It is in this sense that non-brain organs can be thought of as having important – and even life long – effects on states, but still not identity-critical effects on core personality traits. Ultimately, parsing out a long-lasting state vs trait can be somewhat of a semantic distinction and it is not absolute (Chaplin et al., 1988); it is on a spectrum. But I still find it a helpful way of reasoning about this topic.

Everything else other than the brain mediates a state

Basic physiology tells us that organs other than the brain can certainly have state-like effects on one’s personality. However, they can be lost or replaced without changes in one’s personality traits or long-term memories. Hearts, lungs, livers, kidneys, and other organs can be replaced by transplantation. Sensory organs like the cochlea or retina can be at least partially replaced by artificial versions (Stanga et al., 2021). These replacement procedures don’t seem to have clear effects on long-term memories or underlying personality traits. The main function of non-brain organs could be thought of as modulating the brain’s expression of mental capacities.

It’s worth noting that not everyone who loses function in one of their senses feels that it is a loss. For some people, in the right contexts, it can lead to growth. Jorge Luis Borges discusses the ways in which his blindness was a gift in a remarkable lecture.

Some people have claimed that certain organ transplants can cause transfer of memories through some sort of epigenetic mechanism (Liester, 2020). I find the evidence for this to be anecdotal and weak. But even if this were the case, memories and personality would still be instantiated in the brain via electrochemical activity, so the non-brain organs would still not be necessary to preserve if the information in the brain were intact.

One way to think about the fundamental claim behind brain-focused preservation is that the brain is the only part of the body that uniquely mediates traits, while other parts of the body can mediates states. From this perspective, the brain is the only part of the body that is identity critical.

Non-brain nervous system

The spinal cord and other parts of the nervous system other than the brain are worthy of a more detailed discussion.

Spinal cord

Numerous, reciprocal connections exist between the spinal cord and the brain. In fact, it kind of looks like an arbitrary distinction between the brain and the spinal cord when you look at it grossly: 

Human brain and spinal cord; Specimen from the National Museum of Health and Medicine

The microanatomic level tells a different story. The spinal cord tends to be mostly involved in sensory and motor functions, including communication of these with the brain. Whereas the brain is also involved in higher-order functions such as memories, emotions, and personality traits. This is why descriptions of the anatomy of the spinal cord tend to involve motor and sensory fibers that communicate with the brain: