Tintenfisch;180681 said:
Ugh. It always amazes (and disgusts) me that anyone who knows anything about invertebrates (or perhaps that's the problem?) is willing to say 'We can't
prove that they feel pain [despite writhing, retraction from almost certainly negative stimuli, etc.], so until we can, we'll just operate on the assumption that they can't.'
So I'm not sure this is directed at my response or not, but if it is then it's worth responding to. In the strictest sense, we can never
prove any other animal can feel pain. It is a subjective experience by definition, so we can only ever infer from behaviours we observe what the animal is experiencing. Nociception (response to noxious stimulation) is not pain. It is associated with pain, but the two things are not identical, either philosophically or physiologically. To feel 'pain', there has to be a CNS-derived, emotive or affective response to that noxious stimulation.
In mammals, we take behaviours similar to those we see in ourselves and be happy that they are applicable and indicate the same things. This is obviously a lot more difficult as animals get more and more distant, both phylogenetically and in terms of similar appearance, from ourselves. So how should we approach the question of 'does animal X feel pain in response to stimulus Y? We can approach behaviour, or physiology. Behaviour is usually the standard for quick assessment, but it has problems.
We can assess behavioural response to an immediate, noxious stimulus, but it is difficult to separate out what is a reflexive response (withdrawal from noxious stimulation mediated by sensory-motor circuitry with minimal higher-order CNS involvement - nociception) from a supra-spinal, potentially cognitive/higher processing center response - pain. A motor response is almost always initially a reflex - it happens in humans below levels of complete spinal transection, it happens under anaethesia, and after brain-death. Reflexes may or may not be accompanied by higher order, CNS responses. The presence of reflexive withdrawal from noxious stimulation is not in itself evidence of pain.
Duration of response alone is also not sufficient. Most reflexes are quite fast, but if the stimulus is sustained, repeated reflexive responses can continue to occur. So just showing a sustained response to noxious stimulation isn't enough to say Stimulus Y is 'painful' to animal X.
What about the character of the response? Does a writhing motor output necessarily indicate the animal experiences pain? Not necessarily - 'writhing' motor output (waves of movement, basically) can occur without conscious processing. Writhing certainly does occur in response to pain, particularly visceral pain, but alone it may not be sufficient to conclude anything about the way the animal 'feels'.
What about behaviours indicating conscious, ongoing awareness of injury - grooming a wound, showing fear-like avoidance of the wound-inducing context after the stimulation has ceased to act as a cue, long-term motivational changes to behaviour, such as tonic immobility, impaired feeding, lower motivation for social interaction, compulsive behaviours, etc. Many of these behaviours are used to assess the presence of ongoing, spontaneous pain experience, from an unhealed wound, for example. These are quite solid behavioural indicators, but they are not useful for assessing acute pain.
So, behavioural assessment has problems, but can be useful in concert with other types of information. What about anatomy and physiology? We can look at the brain structure and how the brain processes sensory inputs. In humans and other mammals, noxious sensory information coming in from the periphery informs, first, reflexes within the spinal cord, but more slowly, also travels up the cord and into higher-processing centers in the brain, such as the thalamus, amygdala and other higher processing centers. This processing in the brain is what makes us experience pain. So an animal whose sensory neurons lie within simple circuitry that does not connect to integrative or complex processing centers probably doesn't feel pain in the emotive sense. Does that mean it's 'ok' ethically to cause sustained activation of nociceptors? That's a philosophical question that science can't easily answer.
Ok, so what about an animal (such as a cephalopod), that does potentially have the necessary complexity and integrative CNS centers to experience emotive, affective states associated with noxious experience? Just because the brain is large and complex is not sufficient to say the animal experiences pain. It may be necessary, but it is not sufficient. So what do we need in order to make conclusions about pain?
If it can be shown that
1. The sensory neurons can transmit information about noxious stimuli not just to motor reflex centers, but to higher brain areas.
2. Those brain areas are higher-processing centers that have some cognitive or emotive functionality
3. Those processing centers can have some effect on a measurable behavioural response
4. That behavioural response is specific to stimulation by noxious stimulation, but not by other potentially distressing situations (handling stress, isolation, sensory deprivation, etc (i.e., things that are not painful but might be stressful)
and
5. That behavioural response can be attenuated or prevented by either removing sensation from the stimulated area either during or after the noxious input, or by removing, blocking or isolating the higher processing center thought to drive the behavioural output supposedly indicative of pain.
That's a lot of things required to approach a definitive answer to the simple question of 'does animal X feel pain in response to stimulus Y?'
So, at present there is no evidence that cephalopods either do, or do not, experience pain. Yes, people familiar with invert behaviour no doubt observe responses to noxious stimulation, but this isn't sufficient to conclude that the behaviour observed is produced by pain. I feel strongly that assuming an animal
does feel pain until proven otherwise is the best ethical path, but there is also nothing to be gained by concluding this occurs in the absence of empirical evidence.
OB - I suspect the skin is broken and torn in places, allowing quite direct access of sodium onto muscle and nerve fibres. Note the lack of coordination in those movements, which to me suggests minimal CNS-directed movement. That doesn't make it any more enjoyable to observe though.
It was, perhaps, an over-simplification of what I meant to express. In my experience, it is not uncommon for people to use 'we don't KNOW that they feel pain' as a dismissal and/or (in my opinion) unjustified blanket excuse to handle some organisms in a way that should seem inhumane to, well, pretty much anyone. Example: filleting fresh-caught, active fish alive on a boat, then throwing the quivering head and attached spine and remains back into the water, saying 'it will die soon anyway;' I observed this recently and while I am aware that it's probably a very minor example in the grand scheme of things, I still found it quite disturbing, especially as the person was a marine biologist who in theory cares about the sea and its contents. As you have explained (far better than I could), while it is extremely difficult to prove that many animals feel 'pain' (with all the associated complexities), surely the ethical/humane assumption in the absence of such proof is that they can experience some kind of related negative sensation that one should avoid inflicting if possible, all other things being equal.
