The edge of sentience in humans

Mind and AI 5 Minutes

This is the second in a series of posts on Jonathan Birch’s book, The Edge of Sentience. This one is on borderline cases of sentience in humans.

Birch looks at cases involving humans with disorders of consciousness, such as those in vegetative or minimally conscious states, as well as fetuses, embryos, and neural organoids made with human tissue.

For disorders of consciousness, Birch is primarily looking at patients who, due to an accident, stroke, or other malady, end up in an unresponsive or minimally responsive state. This could mean being in a coma, which everyone agrees isn’t actively sentient. But it could also mean being in a PVS (persistent vegetative state) or a MCS (minimally conscious state), where the patient is awake at times, but is completely or minimally responsive to their environment.

Diagnosing when someone is in a vegetative state is tricky. It involves establishing that the patient has no awareness of their surroundings, and shows no volitional behavior. If they do show some minimal awareness, such as eyes tracking movement, then they are upgraded to a MCS. But a key distinction is whether they show any signs of understanding language. If so, they are put in the MCS+ category, if not, the MCS- one.

But diagnosing whether someone is in a PVS, MCS- or MCS+ is very error prone. Birch notes that there is around a 40% chance of misdiagnosis. This is easy to see when PVS patients generally display sleep / wake cycles, but only react reflexively or randomly to what’s going on around them. Birch recounts the harrowing tale of Kate Bainbridge, who was in an unresponsive state for several months, and so diagnosed as being in a PVS. But she was conscious the entire time, including when medical procedures were performed on her. She was only able to reveal her ordeal as her condition improved and she regained some ability to communicate.

Birch’s conclusion is it’s a mistake to have the PVS, MCS-, and MCS+ categories. The chance of error is too high. Every patient who shows sleep / wake cycles should be treated as potentially conscious, and therefore accorded the considerations given to conscious patients, like being anesthetized during painful or invasive medical procedures.

This seems like a relatively easy call to make in cases where a human previously known to be fully sentient may no longer able to display it. But for the other categories we’re about to discuss, Birch’s concept of a “sentience candidate” becomes important.

A sentience candidate is a system we can’t be sure is sentient, but for which there is a realistic possibility, and for which it would be irresponsible not to take “proportionate” precautions. He has a weaker category, an “investigation priority”, for systems that don’t meet the standard for sentience candidate, but could still be sentient. He admits that the standards for “realistic possibility” is unavoidably subjective.

This becomes important when we start talking about the possible sentience of a fetus, which inevitably brings in the abortion debate. Birch argues that abortion rights shouldn’t be linked to the question of sentience, but to body autonomy. That somewhat matches the historical reasoning in US law, where fetal viability, the probability the fetus can survive outside of the mother, is the determining factor of when a state can begin restricting a mother’s ability to abort, at least before Roe v. Wade was overturned a few years ago.

Nevertheless most of us remain concerned about when a fetus can feel pain. For most scientists, that’s unlikely until the third trimester, when the cortical hemispheres come online, or later when the fetus begins showing cycles of REM sleep. However, Birch cites the theories of Bjorn Merker, Jaak Panksepp, and Mark Solms, to argue that there is a realistic possibility of a functional brainstem being sufficient for sentience. If so, he argues that fetuses as early as 12 weeks old, the beginning of the second trimester, become sentience candidates.

In the UK, for mothers considering an abortion and asking if their fetus can feel pain, the current standard is to advise them of the scientific consensus above. But Birch feels that they should be told of the “tremendous amount” of uncertainty involved, and that it’s possible a second trimester fetus may feel pain.

My take is that this is giving a lot of credence to theories that the lion share of neuroscientists reject. It’s also worth noting that proponents of brainstem consciousness tend to define consciousness in a different manner than most scientists. They acknowledge that this is processing well outside the scope of introspection, volitional attention, or overall cognitive accessibility. So what Birch characterizes as tremendous uncertainty, I think is actually the semantic indeterminancy discussed in the previous post. In other words, this may be more about how we define “sentience” or “pain”.

What does that mean for the poor mother asking if her fetus will suffer? It’s obviously not practical to give her a course in the philosophy of mind. On the other hand, I can imagine even a remote possibility of sentience making a difference for some women. Maybe the most honest answer would be to convey the current scientific consensus, but with a caveat that there are views outside that mainstream. I’m pretty sure no answer is going to be without controversy.

When it comes to embryos, the question is what can be done with the surplus embryos from IVF (in-vitro fertlization) procedures. For decades, there has been a 14 day rule. Embryos can be scientifically studied and experimented on until they are 14 days old. For decades, this was an easy standard to follow because the technology didn’t exist to preserve them that long anyway. But that has changed, leading to increasing calls for the limit to be expanded. Birch notes that from a sentience standpoint, he doesn’t think there is an issue before the fetus stage, but notes that the restrictions are really more about sanctity issues than sentience anyway.

Organoids are clusters of cells grown from human stem cells in order to study the tissue of a particular organ. Since it’s human cells, the results may be more reliable than studying the same organs in other species, and it offers an alternative to animal testing. Neural organoids are clusters of neurons grown for studying brain tissue. But since their development, there’s been anxiety about whether these clusters might have a form of sentience. I concluded myself a while back that this was very unlikely, but admitted that I’d get more anxious as what was grown became more structurally similar to a complete brain.

Birch reaches a similar conclusion, arguing that if a neural organoid ever had a brainstem, either through innervation or by artificial means, it would become a sentience candidate. (It’s widely agreed that the brainstem is necessary to “power” the cerebrum, even if it isn’t the “seat of consciousness”.) I’m not sure that, in and of itself, would be enough for me. I’d need to see more subcortical supporting structures, like the amygdala, hippocampus, etc. And it’s hard in practice to imagine any kind of functional consciousness without a body of some kind attached, even if only a virtual one. Add all that in the mix, and I’d be pretty nervous that we’re getting to a real life brain-in-a-vat type scenario. But we still seem very far from anything like it.

As expected, Birch’s is more open to liberal forms of sentience than I am. I expect this to get more pronounced in the next section on animals. But the human cases hit home in a stronger manner than many of the others might.

What do you think? Is Birch’s standard of “sentience candidate” a reasonable one? Am I being too dismissive of second trimester fetal sentience? Or the possibility of organoid sentience?

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34 thoughts on “The edge of sentience in humans”

  1. Just read Chapter 10 (the link has a Pdf link).

    I use the mechanics argument. Which is to say, if the physical hardware is not there, and working, synchronised, then consciousness is simply not possible. To me, at least, that seems to be the only quantifiable argument, and source of evidence to shape any and all abortion talk.

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    1. I should have mentioned that this book is open access. Glad you found it!

      On mechanics, I agree, but the Merkers and Panksepps will argue that the hardware is there, in the form of the brainstem. The current scientific consensus is that there are only reflexes there. Birch seems to take the existence of theories saying there’s more as a reason for caution. But as I noted in the post, this wouldn’t be anything like the consciousness you or I are having right now. It might come down to just how much caution we think is warranted.

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      1. Safely, from what we know right now, cut off can be week 28, following full bilateral synchronisation. But, to err on the side of caution (which I fully agree with you on), week 24 is the best ‘time’ we have.

        Citing ‘diagnosis of death’ laws, I love to pose the question: How can you “kill” something that cannot “die”? (which is to say, meet the legal/medical definitions of death).

        Great post, my friend! Excellent find.

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  2. Fascinating post, Mike (and sounds like a fascinating book)! It really looks like we’re finally starting to make strides in locating the physical and functional nature and seat of consciousness/sentience (and leaving the philosophy of consciousness/sentience far behind). The question of neural organoids is an interesting one. I tend to agree that you need a functioning homeostatic body and and brainstem to experience pain. I also understand that open-brain surgeries have been performed while the patient being operated on is playing music on a violin (indicating the patient is not experiencing undue pain). I believe, however, that patients with brain tumors do experience severe headaches when the tumors grow to a certain size but the pain is probably due to pressure against the skull or cytokines crossing the blood-brain barrier, so as long as you don’t add skull, body, brainstem, or immune system cells, it shouldn’t be painful to the neural organoid.

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    1. Thanks Mike!

      My understanding is that there are no sensory neurons in the brain, including any pain receptors. So any pain someone does feel usually comes from outside of the brain. What the surgeons are actually looking for when patients are conscious during open brain surgery are any signs of cognitive changes, which they usually hope to minimize.

      Of course, pain is a sensation that can exist in the brain even in the absence of signals from bodily regions. So I can imagine scenarios where if the insula or anterior cingulate are stimulated, the experience of pain ends up being stimulated. But those aren’t regions on the surface of the cortex, so stimulating them seems like it would take effort.

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  3. Thought you might be interested in this if you haven’t seen it already:

    https://psyche.co/ideas/when-does-the-first-spark-of-human-consciousness-ignite

    I agree with you that it depends on how we define sentience. It seems reasonable to say it’s when something feels pain if that’s what’s at issue in that particular situation, but a broader definition may be preferable in others. As you point out, for some it’s a sanctity of life issue, which can get sticky when we’re talking about ethical treatment. My sense of sentience seems to shift according to the situation, depending on what the consequences are. Which is unfortunate. I tend to think if there are serious consequences…proceed with caution.

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    2. I hadn’t seen that one. Thanks!

      I tend to think asking if babies are conscious is an unproductive question. A better one is, how conscious are they? And in which ways? We know they’re not self reflective. But as the article discusses, they obviously have sensory integration, memory, and expectations. And there’s no reason to expect memory or expectations prior to the third trimester, and late in the trimester at that.

      What would exist in the brainstem stage Birch is worried about is low level sensory integration, but only for reflexive or fixed action patterns. Is that enough for pain? Depends on how we define “pain”, but I think we can say it’s nothing like the pains we think of when we use the word “pain”.

      Birch does make a case that around the 18 week point, we start seeing stress reactions in the fetus to anything invasive. Even if those aren’t conscious, it’s probably worth applying some from of anesthetic in surgery for the fetus’ future health.

      And of course in the case of abortion, we have to balance the mother’s needs against any precautionary principle, since there’s usually no doubt about her sentience.

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    3. From the article:

      “Around 24 to 26 weeks’ gestation, the end of the second trimester, the first nerve pathways wire up the cerebral cortex to the body and the outside world. Until this point, virtually no sensory pathways reach the fetal cortex, the largest part of the brain, identified with consciousness in adult humans. ”

      That would mean Roe v Wade got it about right if consciousness is a primary criteria.

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  4. Something I’ve noticed in the discussions here, and I mean no offence by this observation, is the abundance of labels for ideas or approaches or conditions: theories of consciousness, varieties of computationalism, and now types of sentience: PVS, MCS-, MCS. This approach takes a page from Aristotle’s method of doing science, which is to scrutinize natural objects, take careful note of fine distinctions, and attempt to derive a taxonomy, preferably organized into a hierarchy of classes.

    Whether nature always lends itself to tidy classifications, or whether instead we have only awkward mappings onto a continuum which can be divided in many ways for many purposes, is much in the air these days. So the first question for me is what assumptions underpin classifications such as “persistent vegetative state” and “minimally conscious state.” Certainly, hidden in this distinction is the idea that actual vegetables are not conscious. More than that, and perhaps further back in the etymology, is the idea that they are not responsive. In fact, if you put some limp carrots in water, over the course of the day they might perk up. As to whether a vegetative human’s skin, if cut, might scar over the course of the day, I don’t know. But the question is, would that count as a response? What I’m getting at here is that we have a very poor notion of what counts as “consciousness,” and as long as some exasperating fellow like myself can come along and contest whether a vegetable, or a human who is comatose or perhaps just very deeply asleep, is in some sense conscious (because at some level it responds to its environment, and therefore is in some sense “aware”), our attempts at further classification are on shaky ground.

    Nevertheless, the effort to classify what we can observe is surely the root of all science, and if terms like PVS and MCS are rough beginnings, they are at least beginnings. The real issue is the limit to our oservations; for while Aristotle was able to observe beetles and plants, and modern physicists are able to observe tracks in cloud chambers, when it comes to observing states of consciousness we are in a different position. The only real way we can observe them is either introspectively, or by means of correlation; moreover, the supposed correlations can only and ever be presumed. We can name certain physical conditions and physical complexes “PVS” and “MCS”, basing our names on certain presumptions about the inner states correlated with them; but since the inner states are forever inaccessible to outside observers, the supposed correlations can never be much more than reasonable guesses. (That some thinkers would contemplate avoiding this difficulty by denying the existence of inner states, going so far as to adduce convincing philosophical arguments for their nonexistence, is a testament to the disturbing powers of reason over rationality.)

    In the face of all this, my advice to medical practitioners would be to err on the side of caution, and also to put their flowers in water. As for the taxonomists, by all means carry on; centuries from now, some good may come of it.

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    1. Building taxonomies seems to happen in both science and philosophy. In fact I think that’s one of the things philosophy can often be helpful with. I think of David Chalmers’ Type-A materialism, Type-B, etc. I do see a lot of value in these efforts. (I would as someone who often discusses hierarchies of consciousness definitions and favors more precise concepts.)

      Of course, there is a danger in doing this, that it locks us into a way of thinking that might be wrong. I don’t think there’s anything necessarily wrong with the the idea of PVS, MCS+, or MCS- categories, but it changes the type of care provided, and that can be very bad if someone is categorized wrong. I agree with Birch that PVS patients should be treated as though they’re covertly conscious, just in case.

      To your question, even someone in a PVS has responses, but they’re understood to be reflex driven, without any actual volitional thought involved. But it’s not hard to understand why it’s so easy to misdiagnose patients. And to Birch’s point, we can’t rule out the possibility that someone is conscious but unable to respond in any manner to demonstrate it.

      I think a cut healing indicates that the body is definitely still alive, maybe even that autonomic brain processes are still in place, but that kind of biological function doesn’t require an aware subject, at least not without a very liberal version of “aware”.

      Some of the old school behaviorists denied inner states, but I don’t know that there are many of them left. Of course, someone like me accepts that there are inner states, but denies that they are forever unobservable from the outside. Which isn’t to say they’re not extremely difficult to observe, particularly with current technology. But brain scanning technology is getting progressively better, although it remans very early days. Birch discusses that a number of patients diagnosed as PVS were discovered to be conscious with fMRI, although it sounds like that data is currently maddeningly ambiguous.

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      1. I’ve been thinking about some aspects of this, but my way of thinking about these questions is rather different than the general approach here of examining the brain science. My focus might be described as more existential. Instead of commenting here, where my reflections sometimes feel misplaced, I’ve started drafting a reaction to be posted on my own blog, furthering certain themes I like to pursue there. I will of course give you credit and a link for inspiring the post. I hope you won’t mind this indirect, inter-blogging manner of response.

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    1. One possible point is what Simona Ginsburg and Eva Jablonka call “unlimited associative learning”, also sometimes referred to as “global operant” or “instrumental learning”. And in its more sophisticated forms, with episodic memory and imagination, it facilitates a much larger behavioral repertoire.

      Of course, if you see consciousness as something in addition to all that, something ineffable and irreducible, then its point would indeed be elusive.

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          2. Right. In cases of unhealthy ones, do we need an explanation other than its condition? We can look at the evolved mechanisms in healthy or adaptive cases, but when things are damaged, defective, or diseased, it seems like fragments of those evolved mechanisms continuing to work wouldn’t be a great mystery.

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  6. Well that was a “shit got real” kind of post. I don’t think I fully appreciated the real world implications of some of the things you blog about until this post. Questions about consciousness and sentience stop being philosophical when we’re talking about abortion rights and people in vegetative states.

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    1. Hey, you never know when that an abstract topic is going to suddenly become real. Until a couple of years ago, discussions of AI sentience were obviously academic. I still think they are, but admit it’s not nearly as obvious now. For vegetative states, I always think of the Terri Schiavo case, which dragged on for years, eventually becoming a national issue. The struggle people had after seeing the videos of her underscore how hard diagnosis in this area really is.

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  7. I don’t think the issue, for a woman asking if her fetus will suffer, is whether she needs a course in the philosophy of mind. I think it’s reasonable to give her access to several overviews (3, maybe) of varying depth. The half-page version could outline the majority view with the admission that it’s controversial, and mention that the controversy centers on whether “pain” is defined more by attention and cognition, or affect and drives. The 3-page version could sketch the brainstem-focused view as well. The 15-page version could go a little deeper, and the last page would consist of online references.

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    1. You’re assuming that affects are separate from cognition, but that’s exactly the dispute. Of course, that can hinge on what we mean by “affect”. The wide definitional variances probably means words like that should just be left out, and just focus on the idea of what’s necessary for the conscious feeling.

      But I’m on board with a brief statement of the scientific consensus, a note that there are other views, and maybe attached or referenced appendices for those who want to dig deeper. Of course, the way information is presented in those appendices, the emphases on word choices, will be controversial, with inevitable biases hard to remove.

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      1. Good point: I wouldn’t want to imply that affect is separate from cognition. (“Affect” is basically a technical word; laypeople say “emotion”.) So maybe rephrase something like: “the controversy includes whether there are drives that can constitute pain or pleasure, independent of knowledge about the way the organism could get into or out of a situation. So on this view if the organism had a ‘pain drive,’ then if it later got the knowledge, it would immediately try to get out of pain. But the majority view is that you can’t have pain without any knowledge at all, not even where the pain is [or insert other elaborations here].” The point of this statement would mostly be to show that there is a philosophical aspect to the dispute.

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  8. I still wonder about the definition of pain.
    How can bags of electrified, animated chemicals actually experience pain when some of their molecules are divided, heated or crushed? Those molecules, on their own, wouldn’t have any experiences unto themselves. Yet, when bolted to a sentient creature, somehow the splitting, heating and crushing is different?
    DNA tuned life to react violently to these phenomena. OUCH! But that’s really just one chemical compound catalyzing a reaction in another.
    Does a baby feel pain? Did I when they cut a tenth (twentieth?) of my dick off? Did they care? Apparently not.

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    1. Experience in isolation can seem very mysterious. The trick, I think, is backing up and looking at the upstream causes and downstream effects. And then asking if what’s in between is anything other than the relationship between those causes and effects.

      Yeah, back in our day, none of us were anesthetized for circumcision. I’m sure there was screaming and crying. But they assumed it was all reflex. These days I think they first put on desensitizing cream (or something), but I’d guess it still hurts later. Babies go through a lot.

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