Summary: The cortex is generally thought to be the seat of consciousness in human beings. A body of literature indicates that the cortex is not integral to many intuitively conscious behaviors in rats. This suggests that either rats don’t rely conscious experiences to guide their behavior in the way we do, or else that consciousness depends on distinct mechanisms in humans and rats. All told, we should think this body of literature is evidence against the hypothesis that mammals are generally conscious and non-mammalian vertebrates are not.
Epistemic status: I’m not an expert in much of the material surveyed here. Particularly the function of brain regions and lesioning studies in animals. These issues are important and my impression is that very few people have the comprehensive expertise to think well about these things.
Caveat: I’m wary of the decortication studies because they seem so out of line with what I would expect given the prevailing opinions and they are discussed very little in contemporary neuroscience. That said, I have a hard time seeing how they could be grossly inaccurate and I’ve never seen anyone challenge them.
Main ideas are bolded.
Intro
All vertebrate brains follow a similar plan in rough outline. At the highest level, they are generally divided into three parts: the fore, the mid, and hindbrain. In humans and other mammals, the forebrain consists in the cerebral cortex and several smaller structures.
The mammalian cerebral cortex houses a number of specialized sensory processors and muscle controls along with general association regions of less specific purpose. In humans and other apes, the cerebral cortex is also widely believed to be largely responsible for generating our conscious experiences. While structures in the mid or hindbrain control aspects of body regulation and arousal, our experiences are thought to be produced in the cortex. We have successfully mapped out sensory regions and have some understanding of how their activity correlates with conscious contents. Damage to regions of the cortex radically alters cognition and affects conscious experiences in a variety of ways. Moreover, severe damage to the human cerebral cortex destroys all signs of awareness and intentional activity. A human without a cerebral cortex is, for the most part, a living body with no mind.
Primates differ from many other animals in the central role their cortex plays in their cognitive lives. The effects of cortical loss in rats has been studied in depth in a series of neuroscientific experiments (Whishaw 1990)[1], carried out mostly in the 1960s-80s. The results of these studies are striking. The behavior of decorticate rats is remarkably unaffected by extensive damage or removal of their cerebral cortex. The afflicted rats are impaired by the loss of cortical tissue, but not nearly as much as one would expect.
The obvious behavioral implications to decortication noted by experimenters are extremely benign relative to what I would have antecedently expected.
They include:
- A laundry list of small idiosyncratic changes, e.g.:
- Impaired muscle control over the tongue and jaws
- Postural changes while grooming
- Increased use of forepaws during swimming
- Various social changes
- Notably, inferior maternal care
- Difficulty with some complex cognitive tasks
- Inability to reason abstractly about locations
- Absence of food hoarding behavior
I suspect that there are a lot of complicated ways that decortication does change behavior, but which require subtle experimental designs to detect. Surely, the cortex must do a lot of important things to be worth its metabolic cost. However, losing the cortex does not radically affect rats’ ability to survive, navigate their environment, or interact with their peers. They can still find their way around landmarks, solve basic reasoning tasks, and learn to avoid painful stimuli.
This strongly suggests that the loss of the cerebral cortex does not have a major effect on the situational awareness, intentional activity, sensory processing, or learning capacity of rats. Whatever their cortex does, it isn’t necessary for that sort of processing, at least at a rudimentary level.
The extremely different effects of cortical damage tells us something about cognitive differences between humans and other animals, but it isn’t entirely clear what. The phenomenon has been cited in defense of theories that indicate both wide (Merker 2007b) and narrow (Key 2015) distributions of consciousness. I think it does both: the behavioral effects of decortication suggest that consciousness is either restricted to primates or else it is distributed fairly widely outside mammals. Both of these suggestions come at the expense of the hypothesis that consciousness is widely distributed within mammals and generally absent elsewhere. This is not to say that the decortication results show this to be false, but they seem to make it somewhat less likely.
Some Possibilities
I see four main possibilities.
1.) Conscious experiences are dependent on midbrain structures.
Bjorn Merker (2007a) argues that parts of the midbrain produce human experiences; the cortex plays only an ancillary role. While he accepts that the cortex contributes to the variety and nature of our experiences, he suggests that it does so through its effect on activity in the midbrain.
Merker draws evidence from a variety of sources, but it strikes me on a whole to be more evocative than substantial. The importance of midbrain to behavior in other mammals seems to be the strongest evidence, together with facts that we should expect to correlate with this evidence, such as the structural fitness for the midbrain to play such a role. The other most important evidence, in my mind, involves the fact that consciousness is hard to suppress from limited cortical damage alone, no matter where it occurs. However, this is consistent with a diffuse architecture where no single region is responsible. Such diffusion is supported by some neurological evaluations of the Global Workspace Theory (Deco, Vidaurre, and Kringelbach 2021; Mashour et al. 2020).
Merker’s proposal has not been embraced by the mainstream (though it hasn’t been entirely rejected, either). The majority of experts believe that human conscious experiences are primarily a product of the cortex. There is little evidence that conscious activity rests fundamentally on the midbrain. To be plausible, Merkers’ view requires that the particularities of consciousness are settled in the cortex, but only rise to the level of consciousness due to activity in the midbrain. This suggests a division of labor that demands far more evidence that Merker provides.
If Merker were right, however, that would suggest that consciousness does not depend much on the mammalian elaborations of the cortex that so clearly distinguish mammalian brains from the brains of other vertebrates. It seems more likely that consciousness exists in the midbrain machinery shared with rats as well. What’s most distinctive about the human brain isn’t the expansion and development of midbrain regions. So it is less likely that special faculties for human consciousness developed in the midbrain alongside the changes in the cortex.
Furthermore, given that the elaboration of the cortex has correlated significantly with the development of advanced capacities, we should also think it is more likely that animals with a complex midbrain and a comparatively simple forebrain, e.g. most vertebrates, are more likely to share the same mechanisms for consciousness.
2.) Conscious experiences are produced by different cognitive structures.
Many of the tasks that the human cortex performs are accomplished in midbrain structures of rats. This suggests a separate development of these capacities in the lineage leading to primate brains.[2] Since our nearest common ancestors were likely to have brains that were more similar to rats, it seems that these tasks might have ether migrated from the midbrain or developed separately in the cortex.
The shift in responsibilities for visual perception from the superior colliculus to the cortex provides a notable comparison.[3] Visual information in both humans and rats is carried from the eyes to the superior colliculus of the midbrain and to the occiptal lobe of the cortex. In humans, the large majority of connections terminate in the occiptal cortex, where layers of neurons parse and code for aspects of the visual scene. The human superior colliculus instead uses visual information for certain specific purposes, such as directing eyes to objects of interest. The function it serves in humans is generally thought to be unconscious, explaining how it can continue to function in people who claim to lack visual experiences (Schlag 2007).
In fish, the superior colliculus (labeled ‘tectum’ outside of mammals) has a much greater role, and is involved in organizing behaviors around pursuit and flight (Isa et al. 2021). It combines sensory inputs of multiple modalities and is connected directly to motor controls in the hindbrain, allowing it to efficiently manage responses to predators and prey.
Comparative evidence suggests that human ancestors relied on the superior colliculus for primary visual processing with some additional work occuring in the cortex. Gradually, the division of labor shifted so that the cortex became responsible for most visual processing and the superior colliculus was relegated to some tasks for which it remained better suited.
Something similar might have happened with the faculties responsible for consciousness (including, possibly, the superior colliculus). Faculties for consciousness might exist in the midbrains of most mammals, but the cortex has removed the need for these faculties in humans.
It is unlikely that any particular cellular structures migrated from the midbrain to the cortex. Brains evolve by increasing elaboration, not neural transportation. Further, the cortex is arranged in a different fashion from the midbrain. Instead, we should expect that increasing or changing demands caused an expansion of cortical tissue to accommodate the roles previously played by the midbrain. That expansion happened in our ancestors after the ancestral split. When the cortex expanded, some tasks no longer needed to be performed by the midbrain and so they fail to develop, or else have atrophied and disappeared.
This view suggests that consciousness is neurologically cheap. It would have evolved at least twice in our lineage. The second time it evolved it would have had to have been selected despite already functioning in the midbrain.
If consciousness arose twice in our lineage, it seems more likely that it is widely distributed among animals that have brains that are rather different from ours. This would suggest that something about consciousness provides value to faculties perception and action. As soon as the faculties primarily responsible for perception and action changed, consciousness developed in the new locale. We should expect it to occur widely among creatures with moderately complex behaviors, even if they lack regions comparable to either our cortex or our midbrain.
3.) Decorticate rats are not conscious.
There is a straightforward argument that rats are not conscious, even if they retain an intact cortex. The cortex is known to be essential to consciousness in humans, the only species we’re certain is conscious. The cortex has a critical role in producing many of the behaviors that we take as a clear sign its presence. In humans, it is responsible for the processing of sensory experiences, the weighing of pleasure and pain, producing inner and vocalized speech and most complex action planning. In contrast, the limited effects of decortication demonstrates that it plays a much more limited role in rats. It is harder to see how useful it could be if it doesn’t much help rats find food, navigate mazes, or learn to avoid pain.
Mechanisms of consciousness might have developed separately in the midbrain, but then they would have had to evolve twice, in two separate places. What good reason do we have to think that is so? The mild implausibility of the separate development of consciousness casts some doubt on the consciousness of creatures who do not rely on their cortex for behavioral guidance.
Setting the cortex aside, not everyone agrees that rats are likely to be conscious. The most plausible popular accounts that deny them consciousness (Carruthers 1989) take consciousness to involve higher-order representational states. The thought is conceptual rather than empirical (Lycan 2001): conscious states just are those states we are aware of having. Being aware of having a state is representing ourselves as having it. So something in our brains must represent any state that is conscious.
From an evolutionary perspective, higher-order representations are somewhat odd. What good does it do a brain to model itself?
For human beings, there is an answer I like; higher-order representations may help us to hone our mind-reading abilities. Mind reading is the ability to make predictions about other’s behavior on the basis of an understanding of their mental states. We’re quite good at it. We get better at it by observing our fellows’ behavior, but also by keeping track of our own behavior. We know what makes us angry and how we’re likely to act when we’re angry, what calms us down, etc. We can use that self-understanding to navigate our interactions with other friends and enemies. Introspection involving higher-order representations helps us to acquire this knowledge.
In contrast to humans, the vast majority of animals have no noteworthy experimentally verified mind-reading abilities. Even our closest primate ancestors are comparatively pretty terrible at it. They might predict what other creatures will do, but, as far as we can tell, it is not by understanding how their minds work and certainly not by projecting their self-understanding of their own behavior onto those minds.
If higher-order representations are necessary for consciousness, if they serve mainly to enhance mind-reading abilities, and if most animals have no ability to read minds, then this is a good reason to think that they are not conscious.
Mind reading is one potential use for higher-order representations. There may be others. Higher-order representations might also tend to form even without providing any evolutionary advantage – brains are predictive machines, so perhaps they over generate predictions, not only about the world around them but about themselves. That might be enough for higher-order representations to result. Higher-order consciousness theorists do not always deny consciousness to most animals.
The behavior of decorticate rats is perfectly consistent with the thought that few animals have conscious experiences. Higher-order representational states are typically thought to be cortical, and don’t have an obvious role in explaining rat behavior. If rats had higher-order representations that they lost with their cortex, we wouldn’t necessarily see their absence in any activities monitored in a lab. However, the cortex also isn’t particularly well set up to inspect the inner workings of the midbrain, so it is less likely that rats have cortical higher-order representations of what is occurring in their midbrains. If rats have higher-order faculties in their cortex, it is unlikely that those faculties are carefully representing activities of the midbrain.
Humans have a system that integrates perceptions and actions, produces consciousness, is housed in the cortex, and includes higher-order representational states. Rats have a different system for integrating perceptions and actions. It isn’t housed in the cortex. It might also have higher-order representations within it, but we have no independent reason to think that it does.
4.) Humans have two different sources of conscious experiences
Perhaps humans have some conscious experiences that are dependent on cortical structures and some conscious experiences that are dependent on midbrain structures. Rats share at least the latter.
Once we entertain the possibility that rats possess a conscious midbrain and that a cortical basis of consciousness developed separately in the lineage leading to primates, we should also consider the possibility that humans and other primates retain some conscious experiences in a vestigial part of the midbrain. Just because something took over a function doesn’t mean that it was completely lost in its prior location. It may be in the evolutionary process of atrophying, but it may not have finished that process yet.
The midbrain does continue to perform some sorts of activities that are reminiscent of consciousness, including action selection for saccades. Any conscious experiences produced in the midbrain may or may not be open to introspection. Their separation from the cortex could make them inaccessible from higher-order representations and memory, precluding us from being able to recognize and report their existence.
Conclusion
The surprisingly minor effects of decortication in rats seem to show that the mechanisms for consciousness most likely don’t exist solely in the cortex of both human and rat. If consciousness is generated entirely in the cortex in humans and decorticate rats are conscious, rats must have a different basis of consciousness from humans. It is also possible that rats, and probably most other vertebrates, are not conscious.
If rats have faculties for consciousness in their midbrain, then it is more likely that they share those faculties with other vertebrates. Rats, like other mammals, have a relatively large cortex. The fact that rats have substantially larger brains than reptiles or fish, and the fact that a significant part of the enlargement occurs in the cortex, might naively be taken to suggest that rats are more likely than fish to be conscious.[4] But the fact that rats have a comparatively large cortex isn’t a significant reason to think that they are more likely to be conscious than fish if their faculties for consciousness reside elsewhere.
Therefore, the behavior of decorticate rats suggests that either consciousness is more restricted or else it is more widely spread than we might antecedently have thought.
Bibliography
Carruthers, Peter. 1989. “Brute Experience.” The Journal of Philosophy 86 (5): 258–69.
Deco, Gustavo, Diego Vidaurre, and Morten L Kringelbach. 2021. “Revisiting the Global Workspace Orchestrating the Hierarchical Organization of the Human Brain.” Nature Human Behaviour 5 (4): 497–511.
Herculano-Houzel, Suzana, Jon H Kaas, and Ricardo de Oliveira-Souza. 2016. “Corticalization of Motor Control in Humans Is a Consequence of Brain Scaling inCould functional neuroplasticity have allowed previously unconscious brain structures became conscious after some time? Primate Evolution.” Journal of Comparative Neurology 524 (3): 448–55.
Isa, Tadashi, Emmanuel Marquez-Legorreta, Sten Grillner, and Ethan K Scott. 2021. “The Tectum/Superior Colliculus as the Vertebrate Solution for Spatial Sensory Integration and Action.” Current Biology 31 (11): R741–R762.
Jerison, Harry J. 1973. “Evolution of the Brain and Intelligence.”
Key, Brian. 2015. “Fish Do Not Feel Pain and Its Implications for Understanding Phenomenal Consciousness.” Biology & Philosophy 30 (2): 149–65.
Lycan, William G. 2001. “A Simple Argument for a Higher-Order Representation Theory of Consciousness.” Analysis 61 (1): 3–4.
Mashour, George A, Pieter Roelfsema, Jean-Pierre Changeux, and Stanislas Dehaene. 2020. “Conscious Processing and the Global Neuronal Workspace Hypothesis.” Neuron 105 (5): 776–98.
Merker, Bjorn. 2007a. “Consciousness Without a Cerebral Cortex: A Challenge for Neuroscience and Medicine.” Behavioral and Brain Sciences 30 (1): 63–81.
———. 2007b. “Grounding Consciousness: The Mesodiencephalon as Thalamocortical Base.” Behavioral and Brain Sciences 30 (1): 110–20.
Schlag, John. 2007. “Should the Superficial Superior Colliculus Be Part of Merker’s Mesodiencephalic System?” Behavioral and Brain Sciences 30 (1): 105–6.
Whishaw, Ian Q. 1990. “The Decorticate Rat.” In The Cerebral Cortex of the Rat, edited by B. Kolb; R. C. Tees, 239–67. The MIT Press.
Being sympathetic to rats, I’m somewhat uncomfortable engaging with work carried out on rodents because so much of it is unnecessarily cruel. Still, I think that the work on decorticate rats is likely to advance our understanding of animal consciousness and is far less cruel than the population control methods used widely throughout society. ↩︎
It is also possible that these capacities exist in both places in man and rat, so that the duplication of capacity predated the ancestral split. This seems to me to be unlikely. ↩︎
See also changes in the corticalization of motor control (Herculano-Houzel, Kaas, and Oliveira-Souza 2016). ↩︎
Rats have brains about 2-10 times larger than reptiles, amphibians, and fish of comparable body size (Jerison 1973). Decortication removes about 40% of the brain size (including subsequent atrophy of remaining brain regions). So rat brains are still larger after decortication, but less drastically so. ↩︎
I'm curious how these claims square with numerous studies showing that damage to particular cortical regions (eg the anterior cingulate cortex or the insula cortex) do impair pain behavior in mammals. For example:
LaGraize, S., Labuda, C., Rutledge, R., Jackson, R., & Fuchs, P. (2004). Differential effect of anterior cingulated cortex lesion on mechanical hypersensitivity and escape/avoidance behavior in an animal model of neuropathic pain. Experimental Neurology, 188, 139–148.
Dong, W. K., Hayashi, T., Roberts, V. J., Fusco, B. M., & Chudler, E. H. (1996). Behavioral outcome of posterior parietal cortex injury in the monkey. Pain, 64, 579–587.
The contrast between the apparent effects of partial and total damage are perplexing. The cortex surely does a lot of work in sensory processing and action selection, even if it isn't strictly necessary for a lot of behaviors. This sort of thing makes me somewhat wary of trusting the decortication studies too much. That said, it isn't obvious to me why they should be misleading.
The only study of nociception in decorticate rats is included here, in the learning section:
Kolb, B., & Whishaw, I. Q. (1981). Decortication of rats in infancy or adulthood produced comparable functional losses on learned and species-typical behaviors. Journal of Comparative and Physiological Psychology, 95(3), 468–483.
Decorticate rats do learn to avoid a source of shocks, apparently very quickly, but do not engage in a response common to the control rats, burying the source in sawdust. Whishaw suggests this may be the result of motor impairments.
Merker offers one way to square the difference that makes some sense to me. He points to the Sprague effect, in which some deficits caused by loss of the visual cortex of one hemisphere can to some extent be mitigated by damage to the contralateral superior colliculus. Merker suggests that what is going on is that the loss of the visual cortex in one hemisphere creates an unbalance and that balance is partially restored by the damage to the contralateral superior colliculus.
The frontal cortex takes part in action selection with input from the ACC and insular cortex. If it becomes disinhibited by the loss of the ACC / IC, then it may exert an overriding influence on midbrain faculties for action selection that could otherwise appropriately respond to noxious stimuli. Perhaps the midbrain gets a vote in what to do, but that vote is overwhelmed by the disinhibited cortex.
For Possibility 3, I guess you mean more specifically “Decorticate rats are not conscious, and neither are intact rats”, correct?
If so, I think you’re prematurely rejecting, let’s call it, Possibility 5: “Decorticate rats are not conscious, whereas intact rats are conscious.”
I think it’s just generally tricky to infer consciousness from behavior. For example, you mention “survive, navigate their environment, or interact with their peers… find their way around landmarks, solve basic reasoning tasks, and learn to avoid painful stimuli.” But deep-RL agents can do all those things too, right? Are deep-RL agents conscious? Well, maybe you think they are. But I and lots of people think they aren’t. At the very least, you need to make that argument, it doesn’t go without saying. And if we can’t unthinkingly infer consciousness from behavior in deep RL, then we likewise can’t unthinkingly infer consciousness from seeing not-very-different behaviors in decorticate rats (or any other animals).
I also am a bit confused by your suggestion that decorticate-from-birth rats are wildly different from decorticate-from-birth primates. Merker 2007a argues that humans with hydranencephaly are basically decorticate-from-birth, and discusses all their behavior on p79, which very much seemed conscious to both Merker and the parents of these children, just as decorticate rats seem conscious to you. We don’t have to agree with Merker (and I don’t), but it seems that the basic issue is present in humans, unless of course Merker is mis-describing the nature of hydranencephaly. (I don’t know anything about hydranencephaly except from this one paper.)
(My actual [tentative] position is that, to the limited extent that phenomenal consciousness is a real meaningful notion in the first place, decorticate rats are not conscious, and intact rats might or might not be conscious, I don't know, I’m still a bit hazy on the relevant neuroanatomy. I’m mostly a Graziano-ist, a.k.a. Attention Schema Theory.)
(My take on superior colliculus versus visual cortex is that they’re doing two very different types of computations, see §3.2.1 here.)
(Separately, mammal cortex seems to have a lot in common with bird pallium, such that "all mammals are conscious and no birds are conscious" would be a very weird position from my perspective. I've never heard anyone take that position, have you?)
That was what I meant when I started writing the section. When I finished, I decided I wanted to hedge my claims to not completely exclude the possibility you mention. In retrospect, I don't think that hedge makes a lot of sense in the context of my overall argument.
It would be a mistake to infer from such behavior to consciousness without making some assumptions about implementation. In the typical case, when people infer consciousness in animals on the basis of similar behaviors, I take it that they implicitly assume something about similarity in brain structures that would account for similarities in the behaviors. This doesn't seem to hold for RL agents who might use radically different architectures to produce the same ends. It also seems to hold only to a much lesser extent in animals with different sorts of brains like octopi (or possibly, given these studies, rats).
I'm not completely unsympathetic with the thought that the cortex is necessary for consciousness in rats.
Faculties for consciousness might exist in the cortex just to help with complex action planning; when the cortex is lost the behavioral effects are minor and revealed only by studies requiring complex actions. If it is plausible that rats have conscious experiences produced solely within their cortex, it would undermine my claim about the overall upshot of theses studies.
I do think it is somewhat counterintuitive for consciousness to exist in rats but not be necessary for basic behaviors. E.g., if they feel pain but don't need to feel pain in order to be motivated to avoid noxious stimuli.
It has been awhile since I've looked through that literature. My recollection was that the case was very unconvincing, and a lot of it looked like cherry-picked examples and biased reasoning. The important point is that decorticate-from-birth humans don't have the ability to act nearly to the extent that rats do. They can orient towards interesting phenomena and have some control over muscles for things like smiling or kicking, but they can't walk into the kitchen to get themselves a snack. I also think it is important that rats exhibit these capacities even when they lost their cortex in adulthood.
I've heard the similarity claim a lot, but I've never been able to track down very convincing details. Birds are clearly very smart, and their palliums have evolved to solve the same sorts of problems as our cortices, but I would be surprised if there were strong neuroscientific grounds for thinking that if one group were conscious, the other would be too that didn't depend on behavior.
As for whether anyone thinks that, Brian Key or Jack Rose have denied consciousness to fish specifically because the differences in their forebrains. I'm not sure what they would say about birds.
On section "3.) Decorticate rats are not conscious", for what it's worth, I lean towards higher-order-ish illusionist theories*, and I'd guess that mammals and birds have some higher-order representations/do some self-modelling, enough to be conscious on such theories that don't require full self-awareness. See my comments here and here for some behavioural evidence. I'd also want to check for this kind of behavioural evidence in (functionally or physically) decorticate rats before concluding either way about their possible consciousness.
* Something like Attention Schema Theory, although I think we should consider including certain kinds of models of things besides attention, e.g. body schemas (which many animals are likely to have), colour schemas, and so on, as also potentially generating conscious experience. Maybe all that will matter ethically will be something like schemas of suffering, pleasure and/or desires. I don't give much weight to theories that require full self-awareness.
Do you mean people in general? Or, in EA/neuroscience/consciousness research, ...
Could you share any resources that suggest otherwise? It could be also interesting to seem them on a timeline.
If 'mind' is interpreted as "awareness and intentional activity" and "body regulation and arousal" is not considered 'living.'
So, it can be argued that healthy rats are unaware and unintentional and thus do not live?
Is it that what makes us 'a species with a prominent cortex' is care (I mean the reverse of causality)? How does k- and r-selection relate to a species cortex properties (and to consciousness)?
Can individuals with no or relatively non-prominent cortex be really 'present in the moment and place?' Would then species with 'lesser' cortex than humans be much happier if they feel well in a place and are fed and sadder if they do not than humans do because humans 'carry' some memory and plan?
Out of curiosity, do you know of any designs or labs?
Only rats were studied so conclusions about various brains and nervous systems cannot be stated. Is it that this reasoning could suggest that primates would be more conscious than other species but not that these species would be non-conscious because cortex does affect rats' behavior somewhat? Also, even if the decorticate rat behaves similarly as one with cortex, it can be that it is less conscious, for example cannot feel closeness with family as much on in specific ways?
Alongside the lines of 4), it could be argued that humans have some consciousness in different parts of the brain, nervous system, cells, and other parts of the body, depending on the definition of consciousness. Thus, humans can 'empathize' with different species by focusing on that part/activating it and deactivating others. For example, species that experience "arousal" but not "intentional activity" can be empathized with by focusing the former while seeking to block the latter.
Are you aware of the Cambridge Declaration on Consciousness? What do you think about it?
Maybe this was unfair. I meant that these issues touch on comparative neuroanatomy, evolutionary neuroscience, animal experimentation, and the philosophy of consciousness, and few people (in academia or out) have much experience in all of them. I also think consciousness is just really hard to think about.
The Merker piece I cite is the prime example of a denial in the contemporary literature. Merker draws inspiration from Penfield and Jasper, who had a similar view in the middle of the last century.
Social animals tend to have significantly larger brains, so I expect k-selection species would have larger brains, and probably larger cortices too, though I'm not entirely sure about how k-selection species compare with closely related r-selection species. Social animals may have a need for mental flexibility empathy that helps account for the value of consciousness, but that is pretty speculative.
I'm pretty confident that humans and other primates have a greater range of possible conscious experiences than rats, and that the complexity of our cortex has something to do with it. The big question is whether the cortex does something that allows for consciousness or whether it just does something that shapes conscious experiences.
I think it is a great piece of marketing, but not based on great evidence. There remains a ton of disagreement on which capacities and which brain regions are responsible for consciousness in human beings. It is overly presumptive to declare that we're confident that other animals have exactly what's necessary for consciousness. The best arguments for animal consciousness come from behavior, not comparative neuroscience.
Maybe this is like blindsight but for the experience of pain? It appears humans with lesions to their primary visual cortex and who report being unable to see can still make good guesses about objects they look at. The lesions still impair performance on some tasks. I think there's a good case to be made that those people totally lack visual experience, as they report (not just being unable to access hidden visual qualia). The same could be happening with decorticate rodents, as rodents with lesions of the primary visual cortex also exhibit some signs of blindsight. So, normal rats could experience pain, while decorticate rats don't pain, even if decorticate rats continue to react in many (but probably not all) of the same ways.
There's some discussion of some (mostly older) evidence related to blindsight across animals in Tehovnik et al., 2021:
Another more recent relevant paper: Mason and Lavery, 2022:
That strikes me as plausible, but if so, then rats are much more competent than humans in their 'blindsight' like abilities. My impression is that in humans, blindsight is very subtle. A human cannot use blindsight to walk into the kitchen and get a glass of water. Rats seem like they can rely on their midbrain to do this sort of thing. If rats are able to engage in complex behavior without consciousness, that should make us wonder if consciousness ever plays a role in their complex behavior. If it doesn't, then why should we think they are conscious?
You might think that we have evidence from comparative neuroanatomy. Humans have some abilities in both places, and something in the cortex adds consciousness. Maybe the same is true for rats. But if so, that would push the questions down the phylogeny to creatures who can achieve as much or more than rats with their midbrains and don't have any complex cortex.
In your note, you state you are uncomfortable with these experiments. Me too. I find them abhorrent. I used to have a couple of pet rats and they are the dearest, sweetest, most curious and intelligent creatures imaginable. The thought that they could have been ‘decortified’ makes me feel sick.
I have spent a lot of time reading on the neuroscience of memory, to develop my understanding of the field, especially relating to the hippocampus. Much understanding here has come from experiments on rats. When/if I finally publish my findings, however, I intend to avoid citing those papers using rat experimentation wherever possible. Imaging technology has advanced to the point where animal lesion studies can gradually take a back seat, and I would hope that eventually they are no longer performed. As Effective Altruists we should be also moving in that direction too, don’t you think? Is examination of consciousness via this type of experiment even at all compatible with the moral standpoint of ‘doing the most good’? I think not.
Once I visited a university physiology lab. The scientists there seemed like nice people. But they thought nothing of turning a gas tap on to kill a vibrant and happy bunch of mice that were extraneous to their experimental needs. The conversation and the laughter went on, while I looked at all those suddenly still, dead little bodies. It was grotesque. Grotesque.
Thanks for highlighting these concerns. This is something I fretted about before writing this, and I condensed my thoughts into footnote 1. Let me expand on them here:
1.) These sorts of studies are long out of vogue. I don't believe my engaging with them (especially on the EA forum, which confers little academic prestige) will encourage any similar experiments to be carried out in the future. I also don't think it will affect the status of the researchers or the trajectory of their careers.
2.) There are a huge number of experiments that are callously harmful to sentient creatures like rats, as you note. Decortication studies stand out because they involve harms to bodily and mental integrity, which we find particularly repulsive, but many experiments in psychology, medicine, and neuroscience routinely involve killing their test subjects. I'm hesitant to disengage from such research (or to refuse to benefit from it, or let other animals benefit from it) entirely.
3.) All sorts of work indirectly contributes to animal suffering. It is conceivable to me that more suffering is caused by poisoning rats / mice around your average university building, or to provide food for the average university conference, than was caused by these studies to the animals involved. Avoiding engaging with work that involves avoidable animal suffering is extremely difficult. I don't think it makes sense to disengage with work just because the harms it causes are more obvious.
4.) Understanding consciousness is important for cause prioritization. These sorts of studies have the potential to tell us a lot that might bear on how we think about projects aiming to benefit fish or insects. If they can help us direct funds more effectively for animals, we should pay attention to them.
5.) Animal activists have a reputation for naivete and credulity. Engaging substantively with science, which necessarily includes studies that cruelly harm animals, may help us to be taken more seriously.
“5.) Animal activists have a reputation for naivete and credulity. Engaging substantively with science, which necessarily includes studies that cruelly harm animals, may help us to be taken more seriously.”
No. ‘Engaging’ with cruel studies and citing them, paying attention to them, means giving them credence. They should be ignored into oblivion. This is a valid standpoint, neither naive nor credulous.
I only skimmed, so may have missed it, but are these conclusions based only on behaviour shortly after (within days?) of decortification, or also much longer? Could functional neuroplasticity have allowed previously unconscious brain structures became conscious after some time? I'd find that surprising, but what neurosplasticity itself can do is surprising! For example, repurposing the auditory cortex in deaf people and or repurposing the visual cortex in blind people, including for echolocation (!). However, these seem to be examples of still existing functions being improved, not totally otherwise absent functions being realized in a different brain region. (I'm just pulling from the Wikipedia page.)
There are a number of studies, and I haven't gone through them but I expect the details will differ. Whishaw is clear though that a lot of basic abilities return in the hours following surgery. It isn't as though the rats return to the helplessness of infancy for a week or so. (Though it is also clear that some part of the return to normal function is a result of re/learning to cope with their deficits.)
I think that isn't crazy, even without neuroplasticity. It might be like what many people think about the case of split brain patients, where hemispheric integration disrupts separate consciousnesses that are revealed following a corpus callosotomy. This seems less likely in the case of decortication because my impression is the midbrain structures aren't as completely integrated into the cortex in the way each hemisphere is with the other, but I could be wrong about that.