Why fish (likely) don’t feel pain

school-of-butterfly-fishby Brian Key

What’s it feel like to be a fish? I contend that it doesn’t feel like anything to be a fish.  Interestingly, much of our own lives are led without attending to how we feel. We just get on with it and do things. Most of the time we act like automatons. We manage to get dressed in the morning, or walk to the bus station, or get in the car and drive to the shops without thinking about what it feels like. Consequently, much of what we do is accomplished non-consciously.

There is an enormous amount of neural processing of information in the brain that never reaches our consciousness (that is, we never become aware of it and hence are unable to report it). I propose that fish spend all of their lives without ever feeling anything. In a recent paper in the academic journal Biology & Philosophy (Key, 2015) I discussed this idea in relation to the feeling of pain. I argued (as have others; Rose et al., 2014) that there is no credible scientific evidence for fish feeling pain.

I will now address the question about whether fish feel pain in this article using a slightly different approach. I propose that by defining how the human brain processes sensory stimuli in order to feel pain, we will be able to define a set of minimal neural properties that any vertebrate must possess in order to, at least, have the potential to experience pain. As an introduction to this argument I first highlight anthropomorphism as a major stumbling block for many people in recognizing fish do not feel pain and then I discuss the difference between noxious stimuli and pain since these terms are often conflated.

Resisting anthropomorphic tendencies

Grey wolves hunt as a pack. They carefully select their prey, and then perform a series of highly coordinated maneuvers as a team, in order to corral their target. Initially, each wolf maintains a safe working distance from other members of the pack as well as from their prey. They are relentless and seemingly strategic with an overall goal of driving the agitated prey towards one wolf. A cohesive group mentality emerges that portrays logic, intelligence and a willingness to achieve a common goal. Eventually one wolf comes close enough to lock its jaws on a rear leg of the prey, before wrestling it to the ground. The rest of the pack converges to share in the kill. There appears a purpose to their collective behavior that ensures a successful outcome.

But is everything as it seems? A team of international scientists from Spain and the U.S.A. has simulated the behavior of a hunting pack of wolves using very simple rules (Muro et al., 2011; Escobedo et al., 2014). Their computer models do not rely on high-level cognitive skills or sophisticated intra-pack social communication. The complex spatial dynamics of the hunting group emerges by having the computer-generated wolves obey simple inter-wolf and wolf-prey attractive/repulsive rules.

For instance, much of the hunting strategy can be reproduced by having each simulated wolf merely move towards a prey while keeping a safe distance from it and other wolves. In this way the prey is driven towards a single wolf in the pack. Simple rules are all that are needed to generate this hunting behavior. There is no need for sophisticated communication between the wolves, apart from visual contact. There is no need for a group strategy, each wolf can act independently to create what appears to be an elaborate ambush.

The lesson is clear. Watching and analyzing animals behaving, either in the wild or in captivity, is fraught with tendencies to describe underlying causes of actions and reactions in terms of human experience. This human-centered explanation of behavior is referred to as anthropomorphism: when humans observe animals responding to a sensory stimulation in a way that reflects how they would react, there is often a strong desire to invoke anthropomorphic explanations.

One can easily imagine that a group of humans closing in on a prey would either communicate amongst themselves or learn from experience how each other is thinking, and hence how they would react to different scenarios in order to achieve a common goal. Because humans so easily reflect on their own behavior, human-like qualities are bestowed on animals spontaneously. For example, when a fish squirms after it is hooked, there is a natural tendency to imagine the pain that the fish is feeling. It seems intuitive. A hook in your mouth would hurt, so why wouldn’t fish feel the same.

Our anthropomorphic and sometimes intuitive view of the world is not, however, always helpful in understanding the behavior of animals (particularly those that are not our close relatives; de Waal, 2009). Yet, even scientists at the top of their profession adopt anthropomorphism, a line of thinking that can camouflage biologically and evolutionarily more plausible explanations of animal behavior.   (However, not everyone will agree. Readers are referred to an essay by Marc Bekoff; Bekoff, 2006).

Why do humans so easily fall victim to anthropomorphism? One could argue that we are hard wired for empathy and hence anthropomorphism, especially given the role of a specialized set of neurons in the cortex (so-called mirror neurons) and subcortical regions which appear to non-consciously drive these behaviors (Corrandini and Antonietti, 2013; Gazzola et al., 2007; Heberlein and Adolphs, 2004).

Defining key terms

One of the common queries raised by discerning readers is that if fish don’t feel pain, why do they then squirm, flap and wriggle about in distress when they are raised out of water? Why do they fight so hard to escape a fisherman’s line? It is a simple and emotionally powerful anthropomorphic argument. That is, if a hook was pierced into your lips and then someone yanked on it, wouldn’t you struggle to escape and free yourself, just like a fish?

Maybe not.  A wild horse submits to a leash within minutes. A bear trapped in a foot snare shortly gives up its struggle. Why does a fish continue to fight in the face of supposedly extreme pain (in some cases, as in big-game sport fishing, fish will relentlessly fight against the hook for 1-2 hours). An alternative view is that fish do not feel pain.

There are two terms that need defining here: fish and pain. When I refer to fish, I am referring only to bony ray-finned fish, since they are the most common experimental fish model and the fish most people are familiar with (these are fish with bones as well as fins that have spikes). The most defining anatomical feature of ray-finned fish is gills. Whales, porpoises, dolphins, seals, otters and dugongs are not fish. These animals are marine mammals; they possess lungs rather than gills.

Pain is a term that many readers will not have difficulty in understanding. Everyone has some vivid recollection of it, after touching something hot or smashing a thumb with a hammer. However, we must be very clear in our definition given the claim that fish do not feel pain. Pain is the subjective and unpleasant experience (colloquially referred to as a “feeling”) associated with a mental state that occurs following exposure to a noxious stimulus.

The mental state is the neural activity in the brain that is indirectly activated by the stimulation of peripheral sensory receptors. A noxious stimulus is one that is physically damaging to body tissues (e.g., cutting, cold and heat) or causes the activation of peripheral sensory receptors and neural pathways that would normally be stimulated had the body been physically damaged.

Gentle touch and warm water are not noxious stimuli. They neither cause physical damage to tissues nor activate sensory receptors and nerves normally stimulated by physical damage. It should be noted that pain is not a necessary consequence of noxious stimuli. For example, there are many anecdotes of people who have experienced traumatic accidents resulting in severe body tissue trauma without feeling any immediate pain. This means that it is possible to cut your skin without feeling pain.

Some basic neurobiological concepts

To feel pain requires that you are aware or conscious of your own mental state. To be aware first requires that you attend to the stimulus. A simple demonstration of this concept is illustrated by asking you to feel the pressure on your ischial tuberosities (the bony parts of the pelvis that you sit on) when you are seated. Before I directed your attention to your backside you were probably not aware of it, but immediately afterwards you became conscious of the feeling of your seated position. To feel a sensory stimulus requires attention to that stimulus (in this case, pressure on the ischial tuberosities).

Awareness of the mental state associated with peripheral stimulation of sensory receptors arises as a result of the process of attention. This is called the top-down attentional system since it involves the frontal lobes, supposedly the highest hierarchical level in the brain (Collins and Koechlin, 2012). However, attention is not always under conscious or voluntary top-down control. It is possible for the sensory stimulus itself to non-consciously activate attentional processes in what is referred to as the bottom-up attentional system (Driver and Frackowiak, 2001). A relevant and simple example would be to accidentally stand on a sharp object while walking. In this case the noxious stimulus activates attentional circuitry and causes awareness (pain, in this example). In humans, the cerebral cortex in the frontal and parietal lobes of the brain is intimately involved in attending to input from our sensory receptors. In summary, feeling pain requires the activity of neural circuits associated with attention.  Once the brain is attending to a sensory stimulus then it becomes possible to subjectively experience a specific sensation.

These top-down and bottom-up attentional mechanisms are not specific to feeling pain. Much of our understanding of their contribution to processing of sensory stimuli comes from the visual system (Corbetta and Shuklman, 2002; Buschman and Miller, 2007).  What is pertinent to our discussion is that both the top-down and bottom-up attentional mechanisms are dependent on specific neural activity in the frontal and parietal areas of the cerebral cortex, respectively.

What is the cerebral cortex?

In everyday language the cerebral cortex is the “grey matter.” This grey matter is a thin outer covering of the mammalian brain that typically consists of 3-6 discrete horizontal layers of neurons and their processes. These layered neurons are interconnected vertically to create minicolumns or canonical microcircuits that are repeated across the whole surface of the brain. Each of these minicolumns is interconnected horizontally to produce a massively powerful processing machine.

These canonical microcircuits can be likened to integrated circuits or microprocessor chips in computers. As computers have evolved, more and more circuits have been added to their chips (you may remember the progression in personal computer evolution from 286 to 386 to 486 to Pentium and Core chips). The cerebral cortex has evolved by both increasing the complexity of the canonical microcircuit from 3 layers to 6 layers of neurons (the latter is called the neocortex) and by adding more and more of these “chips,” leading to an expanded surface area of the cortex (Rakic, 2009).

Pain is in the cerebral cortex

Pain causes elevated electrical activity in at least five principal regions in the human forebrain: the anterior cingulate cortex (ACC), the frontal and posterior parietal cortex, the somatosensory (S) regions I and II, the insular cortex, and the subcortical amygdala. These five regions form a core, interconnected circuit that is referred to as the pain matrix (Brooks and Tracey, 2005).

However, just because there is electrical activity in a particular brain region during pain does not mean that that region is responsible for the sensation. For example, while the amygdala is active during pain it is involved in modulating the pain (as well as many other things), rather than producing the feeling of pain. This has been clearly demonstrated in ablation studies in both rats and rhesus monkeys. These animals continue to quickly remove their tails away from a noxious heat stimulus even after bilateral ablation of their amygdala (Manning and Mayer, 1995; Manning et al., 2001; Veinante et al., 2013). Consequently, it is reasonable to remove this subcortical region from the matrix responsible for feeling pain.

On this criterion, the ACC also does not belong to the feeling-pain matrix. Lesion of the nerve fibers arising from the ACC is called cingulotomy and has been practiced clinically for over 50 years to relieve intolerable pain. However, patients continue to feel pain after this surgery — they just no longer seem to be bothered by the presence of their pain (Foltz and White, 1962). Thus, the ACC is not responsible for feeling pain per se. The frontoparietal nexus is likewise associated with attention to pain rather than the actual feeling of pain (Lobanov et al., 2013).

There is compelling evidence that SI, SII and the insular cortex are the essential components of the pain experience. For example, there is an interesting clinical case of a patient who had ischemic stroke that selectively damaged a small portion of SI and SII in the right side of the brain (Ploner et al., 1999). This patient could no longer perceive any acute pain in response to thermal noxious stimuli or pinprick to the left hand (Ploner et al., 1999). In addition, numerous other clinical studies have revealed that when cortical lesions involve a substantial portion of SI, patients no longer experience any pain (Vierck et al., 2013). Likewise, patients with lesions to the SII-insula cortex have been shown to either lack the sensation of pain (Biemond, 1956) or have altered pain perception (Starr et a., 2009; Veldhuijzen et al., 2010; Garcia-Larrea, 2012a and 2012b).

Another important test of whether a brain region is responsible for pain is to selectively stimulate that region with electrical current.There are only two cortical regions that have ever been shown to cause pain when electrically stimulated (Mazzola et al., 2012): the SII and the insula, which make these two regions the most critical components of the feeling-pain matrix (Garcia-Larrea, 2012a, 2012b).

What does conscious processing of noxious stimuli involve?

I have already described above that the brain must have attentional mechanisms in order to feel pain. But what else does the brain need to do in order to experience pain?  Since pain is, by its very definition, the conscious processing of neural signals arising from noxious stimuli, we should, in the first instance, be asking what does conscious processing in the human brain do. Ideally, if we can identify what conscious processing accomplishes, we should be able to relate this to specific neural architectures. Once these architectures are characterized they can then be used as biomarkers for the likelihood that a nervous system feels pain.

Conscious processing is dependent on at least two non-mutually exclusive processes: signal amplification and global integration over the cerebral cortex (Dehaene et al., 2014). Why are these processes so important? Amplification provides a mechanism to increase signal-to-noise ratio and to produce on-going neural activity after the initial sensory stimulus has ceased (Murphy and Miller, 2009). Global integration ensures the sharing and synchronization of neural information so that the most appropriate response is generated in the context of current and past experiences.

Recently, the amount of information transferred across distant sites within the cortex has been quantified using electroencephalography. These quantitative values have been successfully used to distinguish between conscious, minimally-conscious and non-conscious patients (Casali et al., 2013; King et al., 2013). Thus, global integration is a critical defining feature of conscious processing.

What neural architectures enable the cortex to perform signal amplification and global integration? Both of these processes rely on the global propagation of neural information over the cortex surface. Such propagation is achieved by extensive lateral interconnections (axon pathways) between cortical regions. These cortical regions must be reciprocally linked by axons transmitting both feedforward excitatory and feedback excitatory and inhibitory activities (Douglas, 1995; Ganguli et al., 2008; Murphy and Miller, 2009).

In the sensation of pain, amplification involves long-distance attentional pathways associated with the fronto-parietal cortices and their interconnections with the feeling-pain matrix (Lobanov et al., 2013). The SI and SII sensory cortices possess topographical maps of the body that process information associated with the somatosensory system (see Key, 2015). Slight offsets of these maps (at least in human SI) for different sensations has been proposed to allow integration of different qualities (e.g,. touch and nociception: Mancini et al., 2012; Haggard et al., 2013).

This idea has gained considerable support from recent high resolution mapping in primates (Vierck et al., 2013). It is now clear that different sub-modalities of pain, such as sharp-pricking pain and dull-burning pain, are mapped in different subregions of SI. Moreover, lateral interactions between these subregions significantly alter their relative levels of neural activity (Vierck et al., 2013).

Somatotopic maps of noxious stimuli also exist in the anterior and posterior insular cortex (Brooks et al., 2005; Baumgartner et al., 2010). Separate somatotopic maps are present for pinprick and heat noxious stimuli within the human anterior insular cortex (Baumgartner et al., 2010). This segregation of sensory inputs raises the possibility that integration occurs between these two sub-modalities and also allows these sub-modalities to be integrated separately as well as together with emotional and empathetic information that reaches the anterior insular cortex (Damasio et al., 2000; Baumgartner et al., 2010; Gu et al., 2010; Gu et al., 2013; Frot et al., 2014).

Amplification and global integration is also dependent on the local microcircuitry in each cortical region (Gilbert, 1983). The local cytoarchitecture of the cortex (the presence of discrete lamina and columnar organization) is capable of simultaneously maintaining both the differentiation and spatiotemporal relationships of neural signals. For example, separate features or qualities of sensory stimuli can be partitioned to different lamina while the columnar organization enables these signals to be integrated. Both short- and long-range connections between columns provide additional levels of integration.

The six-layered neocortex is well suited for this neural processing. Signals from the thalamus terminate in layer 4 and are then passed vertically to layer 2 within a minicolumn. Activity is then projected to layer 5 within the same minicolumn. Strong inhibitory circuits involving interneurons refine the flow of information through this canonical microcircuit (Wolf et al., 2014). The layer 2 neurons project to other cortical regions (local and long-distance), while layer 5 neurons project to subcortical regions.

Taken together, if the signal is strong enough and if sufficient information is transferred and integrated, then the feeling of pain emerges (at present, how this occurs remains a mystery).

In summary, to the best of our knowledge, for any vertebrate nervous system to feel pain it must be capable of transferring and integrating a certain level of neural information. I contend that such a nervous system must have, at least, the following organizational principles:

1. An attentional system to amplify neural information;

2. Distinct topographical coding of different qualities of somatosensory information;

3. The integration of different somatosensory information both between modalities (e.g., touch and pain) and within a single modality (sharp versus dull pain);

4. Higher-level integration of noxious signaling with other relevant information (e.g., emotional valence). This requires significant long-range axonal pathways (feedforward and feedback) between brain regions integrating this information;

5. Laminated and columnar organization of canonical neural circuits to differentiate between inputs and to allow preservation of spatiotemporal relationships. The lamina must be capable of processing inputs as well as outputs to either higher or lower hierarchical regions while maintaining meaningful representations of the neural information. The lamina must possess strong local inhibitory interneuron circuits to filter information;

6 Strong lateral interconnections (both local and long distance) between minicolumns to maintain integrity and biological relevance of processing in relation to initial stimulus.

I propose that each of these features is necessary but not sufficient for pain in vertebrates. On this basis it should be concluded that fish lack the prerequisite neuroanatomical features necessary to perform the required neurophysiological functions responsible for the feeling of pain. Fish lack the distinct topographical coding of spatiotemporal integration of different somatosensory modalities; they lack the higher–order integration of somatosensory information with other sensory systems; and they lack a laminated and columnar organization of somatosensory information. What, then, does it feel like to be a fish? The evidence best supports the idea that it doesn’t feel like anything to be a fish. They are non-conscious animals that survive without feeling; they just do it. There is nothing heretical about this idea. For much of our lives, we humans also exist non-consciously.


Brian Key is a Professor of Developmental Neurobiology in the School of Biomedical Sciences, University of Queensland. He is the Head of the Brain Growth and Regeneration Lab there. The Lab is dedicated to understanding the principles of stem cell biology, differentiation, axon guidance, plasticity, regeneration and development of the brain.


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127 replies

  1. Like often in science, the crucial philosophical steps are taken before the science starts. To me these steps are taken here:
    “Pain is a term that many readers will not have difficulty in understanding. Everyone has some vivid recollection of it, after touching something hot or smashing a thumb with a hammer.”
    “Pain is the subjective and unpleasant experience (colloquially referred to as a “feeling”) associated with a mental state…”
    “To feel pain requires that you are aware or conscious of your own mental state.”

    What is the picture here more philosophically. I suspect it is something like this:
    Pain is a name of a private “object”, the subjective experience of pain. We all know what pain is because we have experienced it, and this is how we learn the meaning of the word “pain”, i.e. by connecting the name “pain” to this inner object by a kind of inner perception where we direct our attention to it. The inner object is private because only I can feel my pain. And so, I can only infer the pain of others from their pain behavior (verbal or otherwise) or perhaps from their brain states.

    If I interpret his picture correctly (and it is really a picture, because vague, and not yet a proper theory), it is quite familiar to students of philosophy. It is exactly the kind of Cartesian picture of mind that has been criticized in philosophy since Wittgenstein.

    As is often pointed out this picture leads very quickly to, for example, the problem of other minds, the inverted spectrum scenarios and the mind-body problem. These problems seem almost impossibly hard metaphysical problems. A Wittgensteinian dissolution of these problems is, without going in to details, that the picture is confused and so the problems are pseudo-problems, or at least have not yet been given meaning. The picture is very seductive and we can’t let it go, so the problems seem like real problems and even obvious problems, so we try to solve them by building complicated theories (scientific and metaphysical theories).

    If Kay takes the Cartesian approach (assuming my interpretation) his whole question is also in danger of becoming a pseudo-problem, since no coherent question was ever formulated.

    I personally don’t claim to know that fish feel pain, I’m ambivalent about it, but this is not yet an intellectual ambivalence (it is not a fully formed question), but something more primitive. I also am open to these kinds of questions being explored, but am suspicious of this approach, because I’m quite convinced that the picture indeed is incoherent or at least very misleading.


  2. Science Not Getting Animal Brains Yet

    Brian: “Patrice raises the idea that “common sense” tells us that animal brains have the same general purpose as humans. I challenge readers to go beyond their everyday experiences because sometimes “common sense” can be misleading.”

    If animal brains don’t have the same general purpose as ours, what could their purpose be? And how come we developed a different purpose?

    What is the purpose of a human brain? Surviving. If animal brains are not for surviving, what are they for?

    All and any animal brain is there to do exactly what the human brain is doing.

    A case of the function defining the tool.

    Conventional evolution theory looks at the evolution of organisms. But there is a higher level of evolution: ecological evolution. And an even higher one: the evolution of functions. For example, the function of flying was evolved by insects, pterosaurs, birds and bats.

    Once flying had been invented by insects, it created its own ecological niche, its own universe in which at least birds and bats could evolve. Because at least birds and bats could eat insects, if they learned to fly.

    The apparition of brain created its own ecological niche, its own evolutionary force.

    This is why the brain capabilities of the most brainy species have been on an ascending trajectory.

    The octopus’ eyes do what ours do. And they look very similar. Even though they evolved in completely separate fashion, and are inverted.

    Vision defines the eye. Specifics follow.

    Same for brains: one needs a reward and punishment (pain) system, and consciousness is useful. A question arises naturally, which philosophers have not answered: what is consciousness for?

    The case of birds is clear: although their brains are completely different, they fulfill all functions found in humans.

    Homo Floresiensis is perhaps even more telling: these 1.1 meter tall hobbits had completely different, much simpler brains. However, they developed sophisticated weapons.

    There too the basic functions were satisfied from completely different neuroanatomy.

    I am not claiming neuroanatomy plays no role, and that all animal brains can have as many functions as human ones: supposedly cockroaches keep on drinking, even when their throats are cut. Some insects seem perfectly dumb. However, wasps are smart. And they seem to experience pain. (I have experimented with wasps; my anti-wasp method is to hit them. Once hit, or even after a near-miss, they deduct that they better go somewhere else; conversely, wasp will makes it dangerous to approach a wasp nest!)

    Socratic claimed that wolves do not discuss hunting. Pendantry rightly asked him how he knew. We know little about animal languages.

    It was just discovered that “… chimpanzee referential food calls are not fixed in their structure and that, when exposed to a new social group, chimpanzees can change their calls to sound more like their group mates.”

    Drawing massive, drastic conclusions, when one knows so little? Is that “scientific”? Is that prudent? Is that wise? Is it related to intellectual fascism?

    Liked by 1 person

  3. Hi all, wish I had had more time this week(end) be engaged on this essay. If you have not read the link Massimo provided to the author’s journal article, I highly recommend you check it out. It presents a larger array of evidence supporting his position.

    Brian, again I liked both the essay and the article. I’m highly sympathetic to your line of argument, using an evolutionary/comparative anatomy approach.

    I want to be clear that my first reply regarding neuroanatomy was not trying to suggest that fish have some different structure that directly reproduces everything found in the human brain. I was trying to suggest that they could have an architecture which produces something similar, an unpleasant sensation of some kind regarding physical damage or threat.

    You arguments seem to demand that feeling pain require a level of attention, discrimination, and control of behavior which rats and humans exhibit. But that begs the question if that is what is necessary for sensation of something unpleasant at all, or rather that the architecture seen in other vertebrates allows for greater division of attention (and so the emergence of subconscious activity that is distinct from pure reflex), discrimination of different modalities, and novel ways to deal with noxious sensations (both fear or pain).

    Instead of concluding that everything is non-conscious (relating that to a state we have due to division of attention) perhaps fish are blanket ‘aware’ of more things which we have relegated to not being important for sensation (attention) until it meets certain requirements. And rather than highly descriptive (this pain or fear versus that) it is more generalized. In other words, maybe what we experience is a pain-moderated rather than a pain-mediated world, with our neuroanatomy squeezing the most/best possible information from these kinds of sensations.

    I will address points in your article along these lines in my next post.


  4. Hi Brian, in your journal article…

    1) Section “physiological stress is not pain”, assumes that there should be a direct relation between external stress and cortisol level. That does not seem mandatory, particularly in a more general and context dependent use of pain/fear. It is also not out of bounds that multiple stressors leads to less cortisol. Perhaps the system is adapted to ‘shut down’ or ‘run silent’ given certain levels of threat.

    2) Section “Brain activity in response to noxious activity is not equivalent to pain”, seems especially damaging to making a hard conclusion in your favor. Here it admits noxious stimulus results in activity across several areas of the brain. That is not suggestive of a pure reflex. You state that the authors of these studies argue that what they found is a “necessary prerequisite for feeling pain.” Yes, it does not prove the existence of pain or emotion, but it certainly supports rather than undercuts evidence regarding such a capacity. It is a shame they did not make more detailed analysis of brain regions affected.

    3) Section “Associative learning using noxious stimuli…”, again seems damaging toward making a hard conclusion in your favor. It certainly limits the amount of ‘conscious’ control of behavior in reaction to noxious stimuli, but seems to set out exactly how it could be used… “Clearly, the forebrain was not needed for fish to exhibit escape behaviour, but it was important for learning the association between the light and the unconditioned stimulus (shock).” How is that not potential evidence for a pain/fear sensation relating the timing of two events?

    Given the above it is not clear why the systems and neurochemistry associated with feelings of general stress would be necessary for a system that is basically all reflex. It is of course possible that it stimulates large numbers of supportive reflexes at once (so more efficient than point reflex activity) and that the evolved cortex is what interprets that general engagement of reflexes as ‘fear’ (making that emotional sensation unique to humans). But it does not seem that specific case has been made, to the exclusion of the simpler explanation (it produces stress).

    BTW, on the bacteria video you presented in an earlier reply. To me I didn’t see what you described, but I guess I am jaded from years behind a microscope. You could easily watch all the other bacteria in the same video. They do a lot of moving around based on fluid currents (including vibrations in it). To me the bacteria was simply being pushed by the fluid pressure caused by the oncoming cell, and the various objects around it. There were no escape actions present. I suppose this supports your theme of people anthropomorphizing activity of other organisms, but to me this hurts your case. Over time people can discriminate between the behavior of the microbe (which is just being pushed around) and what fish are doing when they are shocked (actual activity made in defensive fashion).


  5. Brian,

    It’s been a very interesting discussion.

    The following ex-tract is from your abs-tract Massimo linked to.

    “Humans will typically extrapolate feelings of pain to animals if they respond physiologically and behaviourally to noxious stimuli. The alternative view that fish instead respond to noxious stimuli reflexly and with a limited behavioural repertoire […]”

    Seems like at least a false dichotomy as there is more than one alternative view, and the typical human view is highly variable.

    In your post here, I think you are operationalizing pain and using this operationalized meaning outside of the scientific context it was formulated in, both in the introduction and the final paragraph, and this leads to overarching conclusions that are not supported in either usual or more general scientific contexts and discourse.

    Maybe, some more fundamental issue I have are,

    the apparent assumption that, evolution wise, we have animals of pure reflex and animals of non pure reflex,

    and the implication that when we crank back the evolutionary clock we see animals getting more mechanical or computer like, when in fact, though we do see apparently simpler structures, we still see the same underlying biological complexity.


  6. Aravis Wrote

    “I would have, as I have done before. The trouble is that there is virtually no interest, around these parts, in the Wittgensteinian point of view on these sorts of questions. I wind up sounding like some kind of preacher, and no one is convinced. ”

    While I feel I have benefited from the essay and (especially) the comments I haven’t chimed in as those making arguments in the directions of my current impressions have done so better than I can.

    I just wanted to let Aravis know that while I can only speak for myself I have quite a bit of interest in his comments. I always appreciate them, and while it may not seem that they convince a change of any particular commenters mind, at a minimum I think they often plant a seed for viewing a topic in a different light.


  7. Excellent review and discussion. The conclusion, not unexpectedly, seems to be that a human ‘feeling of pain’ can only be appreciated and understood in the context of human anatomy and function. Differences in structure are associated with differences in function in all cases. Extrapolation of our experiences to other species is, therefore, at best, an approximation.

    Most of the attention has been on brain structures, but just as important is the structure, distribution and innervation of sensory receptors. A fish probably does not have a rich supply of pain or touch receptors in its integument since falling and bumping are not major issues in its environment.

    This brings up another issue that has great importance, especially when trying to understand our fellow human beings. There is actually a tremendous degree of variation amongst individual human beings in the structure of their sense organs, their innervation, and in the structure of the brain (inherited and acquired differences). For instance, there is a fourteen fold range in the number of certain cone cells in the retina. Variations in the receptors of smell, taste and hearing are also fairly common.The degree to which these differences affect individual perception of reality is a complete unknown. There are other modulations of perception responses, constitutional and learned.

    Definitive declarations about our consciousness and that of animals appear to be premature.


  8. Hi Aravis,

    > I wind up sounding like some kind of preacher, and no one is convinced.

    Well, perhaps, but I think that has more to do with the way you put your points across rather than what you have to say. I for one would be quite interested in how you would apply Wittgenstein’s insights to this particular question (of all the continental philosophers he is by far the most interesting to me).

    But my suggestion would be that you do so by laying out one particular tenable approach to the question rather than what you usually (appear to) do, which is to assert that there is one correct way to look at it and that all other approaches are indicative of ignorance of philosophical literature and that if we took the time to read A, B and C we would see that we are all terribly misguided.

    I know I harp on about this a little but that is only because I am genuinely very interested in your point of view but find the way you express it to be unproductive at times.

    My own take on the particular question in this article is that pain is a pretty fuzzy, ill-defined term and so it’s impossible to say if fish experience it or not because it is impossible to pin down precisely what we are talking about. Construed broadly enough, I have no doubt that fish feel pain. Construed narrowly, I have no doubt that they do not.

    I do think there is something it is like to be a fish, but I think it is the barest flicker of consciousness in comparison to what a human being experiences. The line between conscious and non-conscious is just as fuzzy, if not fuzzier, than the definition of ‘pain’, so in many cases there is no fact of the matter on whether something is conscious or not.

    Would that line of thinking be roughly in line with Wittgenstein’s views, do you think?


  9. Implicit in Brian Key’s essay is the difference between nocioception and pain. Nocioception is the response of peripheral receptors (small fibers, including free nerve endings) to tissue damage. Pain is a conscious percept that in humans depends on the forebrain, specifically, on activation of certain brain regions. Although nociceptor activation commonly leads to pain, it is also common to dissociate the two: pain can occur without nocioception and nocioception without pain.
    An additional point I think important is that withdrawal responses, and what looks like pain behavior, can occur without pain. The (human/vertebrate) spinal cord is built (hard wired) to have a limb withdraw to a noxious stimulus, such as a pin prick. This can occur in patients with spinal transections who report no pain. Although I’m less certain of this, I’d expect that facial expression of pain can occur as a reflex response to noxious stimulus of the face with out the perception of pain. (anencephalic infants show facial expression of apparent pleasure and displeasure to foods without conscious awareness). The point being that a reflex withdrawal response is not synonymous with pain. If a fish withdraws from, or even if it learns to avoid, a painful stimulus, this is not a strong argument that the fish feels pain. (conditioned aversion does not necessarily require pain).
    The overall point is that this is a complex issue; no easy answers.


  10. Seth Leon said, re Aravis’ ‘Wittgensteinian point of view

    I just wanted to let Aravis know that while I can only speak for myself I have quite a bit of interest in his comments. I always appreciate them, and while it may not seem that they convince a change of any particular commenters mind, at a minimum I think they often plant a seed for viewing a topic in a different light.

    I agree. His ‘Wittgensteinian point of view‘ has enlarged my horizons and stimulated me to think in new directions. He has even started me down the difficult path of learning about Wittgenstein’s thought.


  11. I think there is a very basic problem when we move from concepts like ‘consciousness’, and ‘pain’ which only make sense to us from our subjective experience, and then try to extrapolate to other organisms. I think the farther an organisms organizational structure differs from our own the more assumptions we need to make, and the less reliable our anthropomorphizing becomes. I think this holds whether we are anthropomorphizing based on perceived behavior or some correlation of perceived physical functional & structural correlates.

    For example; DM suggests that if a fish is conscious it’s consciousness is likely a flicker of ours. But if a fish has some degree of conscious whatever that degree of consciousness is might it not be magnified from the perspective of the fish (since that is all it has)? I don’t think we can address questions like that one definitively. I think our conclusions should reflect our uncertainty and that we should err on the side limiting unnecessary suffering where it might be present.


  12. Wittgenstein is endlessly fascinating in the PI. Often, it is not clear whether he’s taking a firm position or is simply suggesting the difficulty of arriving at one. It’s at times more like brain-storming to me and suggesting the limits of philosophy and the constraints in the use of language. I’m not sure this has much more than cautionary value in terms of Key’s argument. But here are some passages from the PI if anyone wants to venture there.
    – – – – –
    245. For how can I go so far as to try to use language to get between pain and its expression?

    246. In what sense are my sensations private?—Well, only I can know whether I am really in pain; another person can only surmise it.—In one way this is wrong, and in another nonsense. If we are using the word “to know” as it is normally used (and how else are we to use it?), then other people very often know when I am in pain.—Yes, but all the same not with the certainty with which I know it myself I—It can’t be said of me at all (except perhaps as a joke) that I know I am in pain. What is it supposed to mean—except perhaps that I am in pain?

    Other people cannot be said to learn of my sensations only from my behaviour,—for I cannot be said to learn of them. I have them.

    The truth is: it makes sense to say about other people that they doubt whether I am in pain; but not to say it about myself.
    . . .
    354. The fluctuation in grammar between criteria and symptoms makes it look as if there were nothing at all but symptoms. We say,for example: “Experience teaches that there is rain when the barometer falls, but it also teaches that there is rain when we have certain sensations of wet and cold, or such-and-such visual impressions.” In defence of this, one says that these sense-impressions can deceive us. But here one fails to reflect that the fact that the false appearance is precisely one of rain is founded on a definition.

    355 . The point here is not that our sense-impressions can lie, but that we understand their language. (And this language like any other is founded on convention.)

    356. One is inclined to say: “Either it is raining, or it isn’t—how I know, how the information has reached me, is another matter.”

    But then let us put the question like this: What do I call “information that it is raining”? (Or have I only information of this information too?) And what gives this ‘information’ the character of information about something? Doesn’t the form of our expression mislead us here? For isn’t it a misleading metaphor to say: “My eyes give me the information that there is a chair over there”?


  13. Dear jkubie
    Thank you for pointing people to the original article. The issues you raise are very important to the argument but were not covered in my essay here, as I wanted to adopt a different approach. I recommend that readers go to the original article for further insight, especially since I paid the publishers $3000 to enable anyone to download the pdf free of charge.


  14. I wish to thank everyone for giving me the opportunity to defend my idea. It has been an enjoyable interaction and gave me a clearer understanding about issues that need better explanation. Everyone has been able to critique my argument. I was provocative and claimed that, in many cases, anthropomorphism stands in the way of understanding. Since I have not had the opportunity to critique why many readers believe fish feel pain (naturally, none of us have time to critique everyone’s ideas), I now ask that you each jot down 6 key dot points that encapsulate why you think fish feel pain. And then seriously critique these points in light of our conversation here on Scientia Salon. (if you don’t think there is enough evidence, you should then list what is missing for you to accept or refute the idea). If nothing else, thinking hurts for sure.


  15. @DM

    If you’re interested in Wittgenstein’s view on this, one way to start would be to do a web search for “Wittgenstein beetle in a box” or “Wittgenstein private language”.

    To be fair to Aravis, this stuff is not easily summarized in a blog comment (at least not in a way that is unlikely to be immediately misconstrued). One needs a decent amount of background learning and conceptualization to get to the point where one is not drawing incorrect inferences about the “Wittgensteinian” view. So you might more profitably view the appeal to reading background material as an informed statement of necessity rather than a dismissal.

    If you doubt this, try to imagine what concepts require some fairly serious background study to understand in your own philosophical viewpoint. Have you ever found yourself thinking that people would probably be more agreeable to and less likely to misunderstand your views if they had a more thorough grasp of computation, Turing completeness, Shannon information, Boltzmann entropy, connectionist processing, cellular automata or whatever else?

    If you’re wondering whether the effort is worth it, I can only say that I’ve found it to be so. Even where I end up disagreeing with him, the disagreement is more like an ongoing conversation. And I haven’t encountered any other philosopher who stretches my thinking more or who makes me more aware of the ways in which my thinking can be wrong.


  16. Professor Key.
    Your last post to me didn’t address my point. Probably my fault. Anyway, I understand that qualitative difference can evolve over time. Our fish ancestors had nothing qualitatively like hands, for example.

    However we’re talking about something we still share with fish, which is behavior that, for the most part, functions as a means of survival.

    Maybe an analogy would help. We also have eyes like fish do. My difficulty is in understanding why it’s correct to say that fish use their eyes to SEE in a way that humans don’t SEE because their eyes are different than ours, but it is not correct to say they display behavior that indicates experience of preference for some sensations over others in a way different than humans experience these preferences because their brains are different than ours.

    Maybe they exhibit preference without having experience? But than questions about consciousness come into play. Can a fish be unconscious? What was happening when I thumped the smelt on the head as a child and they went rigid as opposed to some time later when they started swimming around again? What happens when fish are anesthetized?

    Maybe this is just word games…not that I’m familiar enough with Wittgenstein to know.


  17. Dear Wm. Burgess
    The behaviour you are referring to is hard-wired and independent of forebrain and independent of sensation. This point was noted by jkubie. With regards to anaesthesia – the precise molecular mechanisms are not really understood but in a nutshell the anaesthetic can affect the locomotor regulatory regions in the brainstem, and with increasing dose will gradually dampen most neural activity. If the dose is not too large the anaesthetic will be metabolised or degraded and neural activity will return and the animal will recover (if you instead thump an animal you will cause inflammation that will act like an anaesthetic in the brainstem). Don’t think because the animal is “unconscious”, it therefore must have been “conscious” – that is word-play.


  18. I appreciate that several posters have expressed an interest in my commenting on the Wittgensteinian view of sensations and particular his discussion of the logic and grammar of “pain reports” and other descriptions that we give of our sensations.

    I think I may have given a mis-impression of being sniffy. I said what I said, because I really didn’t think I should keep bashing people over the head with Wittgenstein, given that for the most part, when I have invoked him — and I don’t take a Wittgensteinian view on *every* issue in philosophy — the response has been mostly negative. So, it was a “don’t give people what they don’t want” rather than “I’m taking my toys and going home.”

    That said, this article, by now, is long in the tooth and discussion on it will close tomorrow. I am up to my neck in work, right now, so I am afraid that I *won’t* be able to give an account of Wittgenstein’s observations on the problems with defining sensations subjectively or “privately” as the author is inclined to do.

    That said, for people who are interested in Witt’s take on this, I echo the remarks of Thomas Jones and Asher Kaye. This article also is not bad:


    This is also quite good:

    Edward Sankowski, “Wittgenstein on Self-Knowledge” Mind New Series, Vol. 87, No. 346 (Apr., 1978), pp. 256-261.

    As is Anthony Kenny’s book on Wittgenstein, which you can download here:


    Kenny’s book covers the whole of his thought, not just the stuff on sensations and private language.


  19. Thanks Aravis. Of course, I would very much welcome an essay, or two, by you on Wittgenstein’s relevance to some of the themes discussed at Scientia Salon. No pressure…


  20. Aravis:

    “Too many here with too scientistic of an outlook for Witt. Also, too analytic (and I say that as an analytic philosopher). Continental philosophers get pretty savaged here, as well, irrespective of how highly their work is regarded in the tradition.”

    Too true.

    Seth Leon:

    “I just wanted to let Aravis know that while I can only speak for myself I have quite a bit of interest in his comments. I always appreciate them, and while it may not seem that they convince a change of any particular commenters mind, at a minimum I think they often plant a seed for viewing a topic in a different light.”

    Hear, hear!

    25. It is sometimes said that animals do not talk because they lack the mental capacity. And this means: “they do not think, and that is why they do not talk.” But–they simply do not talk. Or to put it better: they do not use language–if we except the most primitive forms of language.–Commanding, questioning, recounting, chatting, are as much a part of our natural history as walking, eating, drinking, playing.

    (Philosophical Investigations)

    659. Think of the uncertainty about whether animals, particularly lower animals, such as flies, feel pain.
    The uncertainty whether a fly feels pain is philosophical; but couldn’t it also be instinctive? And how would
    that come out?
    Indeed, aren’t we really uncertain in our behaviour towards animals? One doesn’t know: Is he being cruel or
    660. For there is uncertainty of behaviour which doesn’t stem from uncertainty in thought.
    661. Look at the problem of uncertainty as to whether someone else is feeling pain in light of the question whether an insect feels pain.
    662. There is such a thing as trust and mistrust in behaviour!
    If anyone complains, e.g., I may be trustful and react with perfect confidence, or I may be uncertain, like
    someone who has his suspicions. Neither words nor thoughts are needed for this.
    663. The unpredictability of human behaviour. But for this–would one still say that one can never know what is going on in anyone else?
    664. But what would it be like if human behaviour were not unpredictable? How are we to imagine this? (That is to say: how should we depict it in detail, what are the connections we should assume?)
    665. “I don’t know what’s going on inside it right now!” That could be said of the complicated mechanism say of a fine clock, which triggers various external movements according to very complicated laws. Looking at it one might think: if I knew what it looked like inside, what was going on right now, I would know what to expect.
    666. But with a human being, the assumption is that it is impossible to gain an insight into the mechanism. Thus indeterminacy is postulated.
    667. If, however, I doubt whether a spider feels pain, it is not because I don’t know what to expect.

    (Remarks on the Philosophy of Psychology, Volume II)


  21. SciSal:

    “Of course, I would very much welcome an essay, or two, by you on Wittgenstein’s relevance to some of the themes discussed at Scientia Salon.”

    Great idea.


  22. Seth Leon

    > I don’t think we can address questions like that one definitively

    I agree. What I’m really advocating is agnosticism on the subject. All we can be sure about is that whatever it is like to be a fish (if anything), it is certainly very little like what it is to be a human.

    Asher Kay

    > If you’re interested in Wittgenstein’s view on this, one way to start would be to do a web search for “Wittgenstein beetle in a box” or “Wittgenstein private language”.

    OK, but I’ve already come across these ideas and was more interested in how they might be applied specifically to this problem. I think my take on it may not have been a million miles off.

    > So you might more profitably view the appeal to reading background material as an informed statement of necessity rather than a dismissal.

    I think it depends on context. I have no problem with references — I think it’s great to include them and sometimes do myself (perhaps not often enough). I’m just put off when they are provided with an attitude implying “QED, point settled”, and ignoring the fact that there are plenty of further references which would paint a different picture. Again, it’s not about what is said but the way in which it is said that sometimes rubs me the wrong way.

    > And I haven’t encountered any other philosopher who stretches my thinking more or who makes me more aware of the ways in which my thinking can be wrong.

    You appear to take me for someone who doesn’t find Wittgenstein to be interesting, even though I said he is. Whenever I’ve looked into his views I seem to find myself agreeing with him more often than not. He does have a reputation for being difficult though, which has probably put me off doing more than dipping my toes in the shallow end — a recent frustrating attempt at reading’s Kant ridiculous circumlocutions has scared me away from trying any philosophers with such a reputation (although Witt probably isn’t quite as bad?).


  23. Professor Key–your interaction in the comments has been superb. It’s a rare privilege for a ‘main street’ person like myself. Thanks.
    In response to your excellent assignment for us to jot down 6 points about why fish don’t feel pain and critiquing them in light of the discussion, etc. Great idea–and I really hope others will do this. I was only able to come up with 2 points:

    1. I think fish feel pain because they behave as if they do and because, ethically, I think I should regard anything that behaves as if it feels pain as indeed feeling pain. I’m only absolved of this obligation if I can completely account for the fish’s behavior in terms that does not involve pain.

    1.1. critique: We know that our own experience of pain depends on structures in our brain that fish do not have, hence fish do not feel pain. Also, we can point out examples of reflexive reaction to noxious stimula that does not involve pain in our own bodies.

    1.1.a-response to critique: I will find this critique more convincing the more it can be demonstrated that pain is not possible in any other structure of brain than the one we have and share with primates, etc. Cerebellums function as motor and communication controls in humans, but the lady in china speaks and walks and never had one. Examples like this cause one to expect a lot of elasticity in nervous system function. Simply pointing out that fish brains are different than ours doesn’t seem to meet the criteria for why they behave as if they feel pain.

    2. I think fish feel pain because they can learn that if a light comes on, they can escape an impending electric shock if they move to another area of the tank.

    2.1 critique: But learning can be a reflexive reaction as well.

    2.1.a-response: How is this possible? Can learned behavior exist without some sort of recall/memory? What exactly is being remembered when the fish move to the other side of the tank? An explanation for how learning is possible without recall and how recall is possible without a recalled experience–will help me accept that fish don’t feel pain.


  24. I disagree, slightly and in part, with Brian. I think pain is a vertebrate, c-fiber, sensory perception which drives avoidant behavior, all of which fish definitely have. Another biologist, Victoria Braithwaite, wrote a book, “Do Fish Feel Pain, ” in 2010, to claim just this.There may be an analog to such function in invertebrates, but there I am less certain about pain.

    Suffering, though, requires the higher cognitive faculties which Dr. Key says are required for pain as such. He gives a very good review of the relevant neuroanatomy in his post.

    So I have what amounts to a mere difference in definition. I’d say Dr. Key’s “pain” is what I term “suffering.” I agree that it is unlikely that fish can suffer.

    Dr. Brithwaite’s book tries to assert otherwise, but only by claiming that fish have analogous structures to the mammalian brain’s neocortical connections, and I don’t think that part of her book does much more than gesture in the direction of potential future evidence.


  25. Dear Wm Burgess
    Thanks for taking up the challenge. I have an experiment that addresses both of your points that you need to consider in your deliberations. Initially performed on locust it involves isolating a locust limb from the rest of the body and positioning it so that it is above water. When the limb touches the water it receives an electric shock. Amazingly the limb immediately retracts from the water and it learns to maintain a position above the water (remember this is just an isolated locust limb). Now this experiment was repeated using a rat limb and lower portion of the spinal cord and the exact same result was achieved. In both cases the limb acted like it was in pain (your point 1) and it learned to avoid the shock (your point 2).


  26. Here is one article dealing with Wittgenstein’s ideas and animals: “The Difficulty of Language: Wittgenstein on Animals and Humans” pp. 45-64 in the book “Language, Ethics and Animal Life: Wittgenstein and Beyond”. You can read the whole article in Google books:


    One quote from p.56: “A Cartesian mentalist mistake sometimes made by those concerned to combat anthropomorphism is that no matter how great the resemblance between animal and human behaviour is on the ‘outside: what goes on on the ‘inside’ is what our human mental terms really mean. It is thus this inner thing – states of consciousness, experiences, mental processes, etc. – that distinguishes animals and humans and makes the application of certain concepts to animals ‘anthropomorphic’ and illegitimate. The problem with this assumption is that it leaves us with a scepticism about human minds other than our own. Since, so the assumption goes, all we know by direct observation is our own experience we have to infer from the behaviour of the other by analogy with our own case what is going on ‘in him or her. ”

    That quote sounds perhaps too behavioristic, but the point is correct when put in the larger context of Wittgenstein’s philosophy. (She does have things to say about fish that might be even empirically false but that does not affect the article as a whole.)

    Whatever the facts, this post by Brian Key was stimulating, even if I think his philosophical assumptions are wrong, it made me want to read more neuroscience and ethology, that are on my evergrowing list of things to learn.

    (I changed my nickname, I’m the “timantti” from above.)


  27. I don’t know about whether or not they feel pain, but when they can’t get oxygen, it’s pretty clear by their behavior they’re absolutely in a PANIC! Yes, I know it’s relaxing to suffocate fish, sometimes to death, sometimes not, but I hate it. And I look forward to the alien that abuses the guy that decided fish don’t feel pain. I fully expect that alien to go home and write a blog post about how humans apparently don’t feel pain.


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