Science asks awkward questions, doesn't it? I got a link to a recent paper in the BMJ (thanks, SEF!) that asks one of those questions—can fetuses feel pain?—and then takes it apart clinically, coming up with an answer that will make some adults feel pain: that answer is no.
The first step is to work out when the machinery of the nervous system is first present, and when it is simply possible for the fetus to detect unpleasant stimuli. The nervous system has its beginnings early in development, with neurulation at around 3 weeks after fertilization, but it is initially little more than a thread of dedicated tissue that is more focused on raw proliferation than on putting together connections. The first pain sensors grow into the periphery around 7 weeks, and the first projections from the spinal cord to the thalamus of the brain also occur at 7 weeks. Prior to that time, there's just no way for signals to travel to the brain, so sensory information doesn't exist.
The thalamus, now, is a relatively low-level structure, the posterior part of the forebrain. To put it simply, it's a kind of relay station that integrates information from multiple sensory modalities and forwards that on to the higher brain centers of the cortex, that stuff that we think of as more significant in generating conscious thought. It's just not where the action is at. Also, at this early stage, the thalamus has not yet sorted out its structure and doesn't have the capacity for much processing. Neither does the cortex; the next important step is for these tissues to organize themselves into layered structures, and for the thalamus to send projections to the cortex. This doesn't happen until the embryo is 23-25 weeks old. That date represents a minimal, rock bottom bare essential level for the presence of any connections that would confer even a remote possibility of sensory function.
There is evidence that the 25 week old fetus can generate cortical responses to noxious stimuli. There are noninvasive tools to measure blood flow to regions of the brain, and poking needles into preemies and infants (not for fun, but as a necessary part of their medical treatment) elicits elevated blood flow into the somatosensory cortex, a sign that something is going on in their brain. The basic wiring is there.
The author, Derbyshire, is a psychologist, and goes on a little further. There's more to conscious awareness of pain than raw, reflexive nociception. It also requires awareness, a level of experience that enables the mind to associate a pattern of electrical signals with elements of the environment. You can't have pain without an ability to relate it to memory or emotion, and the fetus hasn't yet developed any of those linkages.
So when can we first feel pain? Later than 25 weeks of gestation, that's for sure. As you can see from the summary diagram below, Derbyshire argues that it occurs post-natally—substantially post-natally.
Key developmental stages before and after birth. Colours illustrate gradual emergence of
indicated feature. Solid colour indicates that feature is clearly apparent although not necessarily
fully developed (frontal cortex synaptogenesis, for example, continues into adolescence). Colour
becoming dim again indicates that feature is transient (hyperexcitability to noxious stimulation,
for example, appears at about four months' gestation but is no longer a feature of behaviour
after three months of age).
You might argue with the specific age at which infants are first capable of experiencing pain, but I think his reasoning is sound.
Another obstacle to equating fetal pain experience
with that of adults or older children is the developmen-
tal process that begins after birth. Theories of
development assume that the early human mind begins
with minimal content and gradually evolves into the rich
experience of older children and adults. Although
the view of a neonate as a blank slate, or tabula rasa, is
generally rejected, it is broadly accepted that psychologi-
cal processes have content concerning people, objects,
and symbols, which lay in the first instance outside the
brain. If pain also depends on content derived
from outside the brain, then fetal pain cannot be possi-
ble, regardless of neural development.
Why does this matter? There is currently federal legislation pending that would require fetal anesthesia in all surgical procedures, including abortion, on fetuses older than 22 weeks of gestational age, with large penalties for doctors who ignore the ruling. We're also seeing more and more efforts to carry out corrective surgery on fetuses. Anesthesia does have costs and risks to both the mother and fetus (in particular, I would think, to delicate developing tissues—why risk exposing them to strange chemicals unless absolutely necessary?). I don't think the article is advocating indifference to the possibility of fetal pain, but is saying that an assessment of risks and benefits should recognize that fetal pain is not a serious concern.
Derbyshire SWG (2006) Can fetuses feel pain? BMJ 332:909-912.
Slater R, Cantarella A, Gallella S, Worley A, Boyd S, Meek J, Fitzgerald M. (2006) Cortical pain responses in human infants. J Neurosci 26(14):3662-6.
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Age at which he indicates infants can feel pain is way late, IMHO. Seeing my kid with colic, or being intubated shortly after being born at 34 weeks, makes me think pain is at least ~30 weeks gestation.
Sadly, you're are always going to have baby-fetishists who like to pretend that the only thing stopping a fetus from being a world-class physicist is their inability to speak.
It is this strange idea that innocence and ignorance are the same thing and that both render one "pure".
It's very amusing to me that the very thing (science) that allows people to even KNOW there is a baby present (previously, only the "quickening" was the telltale) is the thing that these same people use to make a religous argument.
I think it is also possible to argue that if the fetus/baby can't remember the pain in any fashion, the net result is that there was no pain. I am thinking specifically of the colonoscopy I had. I did not undergo general anaesthesia, but I cannot remember anything. They could have run metal objects up my ... whatever ... for all I know. Even after I "woke up" I acted as if I were aware, but I have no memory of any of it. My wife could have been slapping me silly for all I know, but I remember nothing and there were no red marks on my face. I could not testify that I felt anything.
I'm reminded of some very right-wing guy who was saying that "leftist" science never touches these issues.
"Science asks awkward questions, doesn't it?"
More importantly, science can answer them.
My daughter was pretty clearly displaying overt symptoms of the sort we associate with "pain" as we understand it when she was a newborn and, for instance, her mother thoughtlessly gave her a couple of glycerine suppositories without lubricating them (I know...), and other times when she's been bruised from falling and such...but I notice also that she seems amazingly capable of forgetting all about the "painful" stimulus in a very short amount of time. That's probably consistent with her behavior being an instinctive reaction, in response to tissue damage, that elicits parental sympathy and care rather than of a conscious awareness of being injured. Which in turn suggests the possibility that the association of that behavior with our emerging self-awareness' perception of "pain" might be a "retcon" of sorts... *ponders*
I agree about the baby-fetishists, though all parents can take some comfort in the recognition that apparently the only thing stopping our 21-month-olds from becoming President of the United States is a constitutional requirement of 35 years of age...
What are the origins of this legislation? Is it being suggested that this anaesthesia legislation is being motivated by the pro-life crowd?
So maybe somebody more knowledgeable than me could update this page on Wikipedia...
I don't think not being able to remember pain equates to not experiencing pain.
I think it is also possible to argue that if the fetus/baby can't remember the pain in any fashion, the net result is that there was no pain.
This doesn't sound like a winning argument to me. If you don't believe in an afterlife, then *every* pain will eventually be impossible to remember; if you do, then *any* pain might eventually be possible to remember.
"I don't think not being able to remember pain equates to not experiencing pain."
I agree. I didn't say "not experiencing pain." I said that the net effect was that there was no pain. I am sure that during the colonoscopy I experienced some sensation ranging from discomfort to pain - excruciating pain, for all I know- but I could not possibly tell you whether I did. To me, that means the sensations don't matter one way or another. The net effect on me in my present state is that there was no pain.
That same idea of amnesia for pain was the logic behind "Twilight Sleep", a anesthesia program that's out of favor now. I have no opinions on the ability of a fetus to perceive pain. On the other hand, I'm aware that denying the possibility of pain is one of rationales for cosmetic neonatal surgeries. Maybe I'm just squeamish, though.
Ray - this is close to reduction to the absurd but it does not follow. Once a person is dead, of course there is no memory. The salient fact is that I cannot remember the pain I purportedly felt only a matter of a few hours later. See above. I did not "forget" that I felt pain. There is no memory of pain to recall.
Just because there's no episodic memory of the pain doesn't mean there's no conditioning effect, or damage from stress. Kid might not remember being attacked by a dog but might show an aversion to dogs anyway. (Hi, HM!)
Unfortunately, I doubt that this bit of evidence will manage to convince The Raving Atheist. Still, it was nice to see PZ call TRA out on his nonsense a week or so ago.
If there is a conditioning effect, then there was a net effect. So far I have noticed no effect, including any aversion to gastroenterologists. Thus there is no net effect to any pain or other sensation that I might have experienced. I also did not mention "episodic" memory. There are other types.
One reason I've put off having my wisdom tooth out was the dentist telling me the anaesthetic choices were: local only, where I would definitely feel pain; general, where I wouldn't feel pain, but which carried a slight risk; and sedative, under which I'd feel pain but not remember it. I couldn't face the local, as my previous experience with local anaesthetic for more minor dental work indicates that I would feel more pain than most people do. And the risks of a general didn't appeal to me. But the sedative posed a huge philosophical conundrum to me. If I didn't remember the pain, wouldn't that be the same as not having experienced it? In the end I decided that it would still be pain, in the same way that a tree falling in a forest still makes a sound, even if there's no-one there to hear it. Unless I was restrained or something, I'd probably try to stop the procedure even if I kept forgetting why.
And from research on people with permanent short-term memory loss from brain damage, it isn't necessarily true that even if one can't consciously remember something, then it won't still be remembered at another level. For example if a doctor shakes hands with a memory-impaired subject and gives them a shock at the same time, the next time the doctor offers to shake hands, the subject will refuse and not be able to explain why, despite not being able to recall the previous meeting.
I lack the knowledge to tell if this was addressed in Derbyshire's paper, but I'm going to be skeptical until I see more research.
Ahhh, phenomena of the mind......I'm glad I study teeth!
Nel, depending on what they mean by sedation, I don't think you should worry too much about it. Sedation is the term they use when you have a colonoscopy, and if it is done correctly, the only difference in experience between that and general is that the recovery time is greatly reduced. There is a kind of philosphical element to the discussion, but I tend to look at it in a pragmatic way. My testimony at this point, and at the point that I became aware of my consciousness, is that I felt no pain. Maybe the doctor who performed the procedure would say otherwise.
As a surgeon I don't buy how far postnatally Derbyshire places the ability to experience pain. The anaesthesia literature, which has studied this question for a long time, places it in the third trimester, as does the neonatology literature (based on studies on very premature infants in neonatal intensive care units).
JAMA has a nice review article from last summer on this very topic. I'll see if I can dig up others.
I think he's pushing the argument a little farther than I would, too...but he's making it on a different basis than you or I would. He's basing it on psychology, that mind can't exist until it has assembled some level of referents to the external world.
Personally, I think this pain issue is a bit of a red herring. While I'm not going to weigh in on either side of the abortion issue in this case, I think a more valid moral argument could be made on whether or not the fetus has any sort of "viability" outside the womb. Is it moral or not to abort a fetus who has developed enough to survive (with appropriate medical intervention) a premature birth? There is certainly a world of difference in development between a one-month old fetus and a 7 month old fetus, after all.
FWIW, my daughter was born at 32 weeks. They had to take blood tests, and I can definitely tell that they hurt. I dunno.
It is possible that a 32 week old fetus might not experience pain but a 32 week gestation premie would because of differences in their environment. A baby lives in a high oxygen environment (room air) and has a partial pressure of oxygen in its blood of around 80 and oxygen saturation of >99%. A fetus, on the othe hand, lives in a low oxygen envrionment (ie only gets the oxygen provided by maternal venous blood) and has a pO2 of around 30 and an oxygen sat of about 70%. The brain, particularly the cortex, doesn't work so well in a low oxygen environment. Most people have only seconds of "usable conciousness" if, for example, they are on a plane that depressurizes (that's why you should always put your oxygen mask on first.) So a fetus might not be able to think or feel pain even if the cortical wiring to do so is present because it simply doesn't have enough oxygen available to run its cortex.
The paper says it's discussing the ability to *feel* pain, but then wanders into a discussion of the ability to *contextualise* it. Not the same thing at all.
Regarding the memory of pain: where do you draw the line? Should we torture people to death as a method of execution, on the grounds that they will not remember in a few hours anyway?
I think the argument makes less sense when extended into infancy: yes, being able to 'contextualize' pain and feeling it are not the same thing. Animals don't have the same psychological structures as we do, but they obviously feel pain. There's a really good reason for newborns to be able to feel pain: pain is a sign that the body's being damaged, and screaming bloody murder to get an adult to fix the problem is the appropriate response for a newborn.
But the fetal neural development stats are purely biolgical; I've seen them before, but it's useful to get them confirmed. 23-25 weeks is about 6 months: the third trimester, when most doctors won't perform an abortion unless the fetus is fatally malformed or the mother will die if she carries to term. And it's a couple of weeks after the onset of quickening (18-22 weeks) which was thought to be the sign of 'ensoulment' by the Greeks.
It's nice to know that practice and science go togther.
PZ said
"He's basing it on psychology, that mind can't exist until it has assembled some level of referents to the external world."
From my own experience, I have to agree with this thought. I was hit by a car, suffered multiple extensive fractures to both legs, pelvis, & shoulder, in addition to severe traumatic brain injury. After five days in a medically induced coma, the brain injury stabilized and the orthopedic surgery was performed. Post-traumatic amnesia lasted another 3 weeks, whereupon I began to be aware of who I was and the world around me.
I have absolutely no memory or knowledge of suffering any pain whatsoever.
I don't know if my experience is even remotely comparable, as I am 45 years removed from being a fetus. However, outside of minimal physical limitations (range of motion, strength) there is no apparent evidence I experienced any injuries, much less pain, even though it must have hurt like hell.
I'm interested to see if this can have any similarity.
When my wife was pregnant our first child, we went to an NBA game (Pacers at Warriors, as if that makes any difference). That was in March of 1994; my daughter was born on August 1, so the baby was at about 5 months gestation. My wife was showing.
The baby was very active. We could feel hands and feet and a butt once in a while (not at 5 months, but later). But the developing baby definitely responded to the noise inside the arena. When there was a lot of noise, that kid really jumped. At 20 weeks, there were clearly startle reactions.
So I'm not really sure I buy into 25-30 weeks for neural development not being complete enough to transmit pain. The ears were definitely working; I don't think the ears told the body to twitch. I think the ears registered noise, which the brain heard, and the brain told the body to twitch.
Maybe sound isn't the same as pain, but don't they both exist on sort of the same level? I'd guess (but, of course, this may just be a wild guess) that they're both at about the same level of complexity.
I don't think it's at all obvious that animals "feel pain". For a start it's not obvious what it means to say that a human "feels pain". It seems obvious to us because we experience it so directly - it strikes us in a way that is hard to ignore, and its very presence makes it hard to reflect on the experience.
With a fetus or a neonate the difficulty of objectivity is multiplied over the case of animals by (quite proper) emotional relationships.
That is why we need science. When the experience of pain is studied scientifically it turns out to be a profoundly subtle, complex thing. It certainly cannot simply be reduced to stimulation of nerve endings (if it were then the treatment of chronic pain would be immeasurably easier). This is also the distinction behind Derbyshire point that while clinical trial have shown that anaesthesia improves outcomes when operating on neonates and is therefore justified, the experience of pain in neonates is a separate question.
The relation of what Derbyshire calls "the content of pain" to biology is part of the hardest question in science - the understanding of consciousness. The literature is clearly vast, but I think the book length references Derbyshire gives are a nice selection (see additional references at http://bmj.bmjjournals.com/cgi/content/full/332/7546/909/DC1 )
WRONG. Doctors used to believe that way, so when debridging dead tissues from burn victims, they used to administer drugs that blocked memory formation but not sensation, reasoning that what they couldn't remember wouldn't hurt them.
That was stopped after patients began having strokes during the procedure from elevated blood pressure associated with the pain.
I hate to wade into this as I am not very science based. But, I do have a question. Why do we only think of pain as subjective? In other words, why are we not measuring physiological changes in the fetus to see if what happens in people is the same as in a fetus. When pain starts in people I think there are chemical changes that occur. Well, actually I know there are in the case of chronic pain. Cytokines are stirred up, to use unscientific language, and chemical signalling and cascades occur. Can anyone measure these things in utero?
My problem with pain being subjective and experiential is this- when we say that it is based on emotion and experience we negate that there are chemical and biological changes that occur in the body, which means that we then dismiss some pain conditions as being "all in the head" . Am I being picky??? Any thoughts?
Of course, if you are planning on arguing from the assertion that fetuses feel no pain (IF that is the case) to concluding that, therefore, you can kill them when you feel like it, you have concluded with a non sequitur.
You need to find some other rationalization for what you want.
That about sums it up...do what you want, and come up with a just so story to justify it.
It appears that DaveScot has been spending his time hunting through Pharyngula's archives for dirt, and he thinks that he's found some.
http://www.uncommondescent.com/index.php/archives/1042
Then, he decides to show everyone what an imbecile he is:
"Actually it makes me feel like doing some pain experiments on PZ Myers. I don't believe he feels pain. All the blood and screaming from my fists pounding his face to a pulp would be nothing more significant than an automobile engine leaking oil and bearings making noise from lack of lubrication. Of course I could be wrong. -ds"
Can't he wait for a different thread, one in which he doesn't try to claim moral superiority? I think DaveScot, despite weighing in at a probable 325 pounds (for sitting at the computer all day every day), wouldn't stand a chance. PZ would lash out with all limbs, like the octopus playing the drums.
Whoever said it's a red herring is slightly off the mark.
It's quite true that the anti-women brigade don't base their 'all human life is of infinite value' arguments (which are bullshit anyway since they obviously consider a woman's life of less value than that of a foetus) on whether foetuses can feel pain from the moment of conception. In fact, a TV news programme the other night had Stuart Derbyshire in the studio along with an anti-women campaigner, and the single thing they agreed on was that this shouldn't be relevant to the abortion debate. But that's exactly why the research is important: even though those people don't genuinely believe that the question of whether foetuses feel pain really matters, up till now they have been more than happy to exploit the issue and use it as a form of emotional blackmail. They can't do that any more without being called out on it.
As a pain neuroscience researcher I have to weigh in... The article in question relies largely on the work of Maria Fitzgerald who is quite likely the world's most highly regarded pain in infants and pain development (from a neuro-anatomy perspective) researcher. Her recent work in J Neuroscience shows fairly convincingly that a cortical response to pain is present at 26 weeks. What the linked article fails to account for is sensitization. This has been one of the major areas of work from the Fitzgerald lab and she has shown, over years of work, that stimuli that accesses the nociceptive pathways (peripheral, spinal and central) during neonatal or infancy periods can predispose animals to greater pain responses later in life. In this regard it is important to note that this is one of the primary reasons that analgesics are used during medical procedures. Sure analgesics help us deal with pain during procedures and shortly thereafter, but one of their major functions is to prevent nociceptive sensitization which can last for weeks to years or even over the lifetime of some patients. This is not a trivial notion as chronic pain is a crippling disease and often shows no overt cause. The current thinking is that analgesics (opiods, NSAIDs and others) should always be utilized in situations where pain is present to help the patient with the present pain AND to prevent sensitization which can occur (and probably does more often than we think) and lead to longterm problems.
While I agree completely that analgesic safety in neonates, infants and children must be the primary focus, I do not believe there is ever a rationale for not using analgesics (or anesthesia) based on the argument that someone cannot feel or contextualize pain (although abortion is clearly a special case). Any medical procedure has the potential to sensitize the nociceptive pathway at the level of the sensory neuron, the dorsal horn neuron or higher areas. The available research clearly demonstrates that analgesics provide good protection against this sensitization.
Sensitization is a good point.
I will also mention that the article in question is not advocating for the abandonment of analgesics -- it's bottom line is about risk assessment, and balancing the benefits of anesthesia against their dangers. It's also not about the ethics of abortion.
DaveScot is insane and stupid, and apparently doesn't know how to either read or think. By some contorted and amoral pattern of 'reasoning', he has come to the conclusion that I'm saying it's OK to do as you will as long as your victim feels no pain: load 'em up with novocaine, and it's all right to kill them. What kind of nutcase thinks so irrationally?
I don't think it's at all obvious that animals "feel pain". For a start it's not obvious what it means to say that a human "feels pain". It seems obvious to us because we experience it so directly - it strikes us in a way that is hard to ignore, and its very presence makes it hard to reflect on the experience.
Now, this isn't my area, but we *did* have an interesting seminar on the subject of animal pain and pain in general about a year ago. The speaker made the distinction between nocicpetion and pain, and went on to make two very interesting points: that nociception can occur without the brain (exemplified by animals whose spinal cords have been cut or decapitated ecotherms responding physically to pain stimuli), and that while nocicpetion was sufficient for classical conditioning, operant conditioning to avoid negative stimuli requires connection to the brain and what could effectively be called pain (these experiments were performed with a level of anaethesia which, in humans, has been shown not to prevent nociception but to prevent pain; the subjects claim they could feel injury and somehow knew it was 'bad' but didn't feel actual pain or discomfort at it).
I'd also note that many animals are smarter than we give them credit for. As anyone who's worked with monitor lizards will tell you, having a brain the size of tootsie-roll certainly doesn't hinder learning, memory, or problem-solving, especially when those abilities are being used to get food or injure the keeper.
Damien: Are you saying that famous patient HM has "learned" an aversion to dogs? That's interesting.
The pain research discussed here also illustrates why having a materialist metaphysics is necessary for scientific research, which no doubt will push some buttons beyond the DaveScots of the world.
some clarification requested here: how impervious is the placental barrier to analgesics? are those proposing legislation requiring such for fetuses suggesting analgesics via the maternal route? or are they proposing administering these directly to the fetus?
if the recommendation is the former, and the placental barrier allows some pertinent analgesics through, isn't the risk to the mom something to be considered?
if the recommendation is the latter, might not the procedure for administering the analgesic increase overall risk to the fetus, at least statistically, irrespective of what it does for pain?
Last night on PBS "Now" they did the South Dakota anti-abortion story. Sure enough, the anti-abortionists there are feeding the line about fetuses feeling pain within just a few weeks. The show also cited the contention that there's no evidence of feeling pain for about 25 or so weeks. The anti-abortionists appear to have the same difficulty with the truth as do the anti-evolutionists, but that's to be expected.
These studies are very interesting to those think something like William Saletan about abortion. To me, there are some deep moral questions in the issue.
Someone mentioned viability of the fetus. I don't think this is a good argument. One could imagine that as technology continues to improve that a fetus will be viable earlier and earlier. It's not so hard to believe that it might be possible one day to do everything from conception to a child outside a mother. At that point, one could say, "I have an egg, I have a sperm. It's viable." Most people would disagree that the destruction of an unfertilized egg, together with a sperm sample, is ethically wrong.
The point of the argument isn't whether this is possible, but that viability isn't a good measure.
I posted a follow-up diary on this over at DailyKos yesterday. I am wondering still why anesthesia for late-term fetuses we intend to kill is seen as something to avoid.
PZ said:
Yet the truth is that late term abortions are rare, the vast majority as a result of serious medical problems. This can include death of the fetus, and there's certainly no reason to administer anesthesia to a dead fetus. There's also anencephaly, where anesthesia would also seem a moot point. But if the issue is deformity, genetic anomaly [Downs, i.e.] or maternal crisis, shouldn't we err on the side of anesthesia for the fetus?
Late term abortions usually occur to a 'wanted' fetus, and it's an emotional decision. If the purpose is to kill the fetus, how is it harmed by anesthesia? Don't we have ethical regulations for euthanasia and against "cruel and unusual" even in the process of slaughter?
Derbyshire's wrong about when babies can feel pain. Check out Maria Fitzgeral's Take [Research Bibliography]. She's a biologist, not a psychologist. As long as there is no certainty on this, shouldn't we err on the side of compassion?
What in the world would be the justification for not providing anesthetic as SOP in abortions after ~20+ weeks, save cases of unusual medical concern for the mother? And I'm pushing it back to earliest firm evidence because my husband distinctly recalls pain in his first three months (starting at 7.5 months' gestation) despite intravenous phenobarb to keep him still for tubes and needles. I recall very distinct, sophisticated emotional pain at 8 months. Derbyshire wants me to believe children can't feel or process pain until 9 months post-birth (when the precocious ones are already walking and talking). Ask your mother about that if she's still around, PZ. She'll tell you the truth about the astounding things human babies learn in their first year of life. Pain comes primal - they don't have to "learn" how to feel it or how to react to it.
This is a scientifically interesting discussion (which I always enjoy). However, I don't think it should affect anyone's position regarding the abortion issue.
Here's why: even if someone is incapable of feeling pain, it is still wrong to kill them.
I guess that makes me part of SH's "anti-women brigade"
Mark Paris wrote:
Joe, All of you people complaining about my speculations insist on taking the argument to the absurd. In the state I was in during my colonoscopy, I doubt seriously that I would have been able to provide any vaguely rational-sounding, not to mention useful, information on anything, including what my name was. I didn't say I was OK with torture. Please read what I said. Or, if it's too hard to understand, just say so and I can explain it further.
I don't think it's at all obvious that animals "feel pain". For a start it's not obvious what it means to say that a human "feels pain".
JK, The logic you employ indicates that you think it's perfectly okay to doubt the existence of something (something that we actually have stupifying amount of of evidence for) until you're able to precisely define it. Not only is this logically unsound, it is also deeply irresponsible.
I think that if you personally got boiled alive, or had your hands and feet whacked off, you wouldn't care very much about "what it means to say that a human 'feels pain'. You would be out of your mind in agony, and that's it.
Since we share common ancestors with other beings, as well as an evolved will to live and survival strategies to avoid pain, it goes to reason that other species have the capacity to feel intense pain, as we do.
Here's a study described by Drs. Sagen and Druyen
It seems that these monkeys are able to sense something (other's pain) that you you are all too ready to deny. Just because you don't understand the neurology behind another being's experience doesn't mean that their experience doesn't exist.
Scientists, in their dispassionate viewing of data, sometimes have their own (perhaps unconscious but definitely self-serving) reasons for ignoring some of it. For example, a medical researcher's ethical choices get a lot more complicated if the creature they're performing research on isn't the unfeeling machine that they had once assumed it to be...
I remember reading somewhere that learning of various sorts starts occurring in the womb. Not learning about things that can't be sensed in the womb, obviously, but testing out various kinds of movement and stuff and gaining some semblance of body awareness.
A person doesn't have to remember learning something, to have been learning at that time. I don't know a whole lot of ordinary people who remember learning language, but they clearly learned it. And a person doesn't have to remember pain to have felt it at the time. Some people can't remember the pain of childbirth afterwards, but I don't know a lot of people claiming childbirth isn't painful. I can't remember post-surgical pain (in which they ran out of painkillers one day) because my brain blocked out the worst of it and I started hallucinating, but I'm utterly sure I was in pain. And plenty of people, for instance, go 30 years, during which they might have broken their leg at one point, and get a head injury or electroshock or something and forget having broken their leg, but it doesn't mean they didn't break their leg or that all experiences prior to that point truly ceased to exist.