Pain as the Perception of Someone: An Analysis of the Interface Between Pain Medicine and Philosophy

Being a physician and pain researcher, I am heavily influenced by some key concepts widely shared by the scientific and medical communities, and these concepts will now be briefly reviewed in order to hopefully create common ground between the present writer and a philosophically trained would-be reader.

The most commonly used definition of pain among pain scientists and health care personnel emphasizes the subjectivity of the pain experience. According to the definition formulated by the international association for the study of pain (IASP), pain is “an unpleasant sensory and emotional experience associated with actual or potential tissue damage, or described in terms of such damage” [14]. The definition emphasizes the subjectivity of pain (it is an “experience”), and it also states that it has both a sensory aspect and an emotional aspect. Further, the connection to actual tissue damage is not obligatory, as it is enough that the experience is “described in terms of such damage”. The definition also has a note that is worth quoting at full length:

The inability to communicate verbally does not negate the possibility that an individual is experiencing pain and is in need of appropriate pain-relieving treatment. Pain is always subjective. Each individual learns the application of the word through experiences related to injury in early life. Biologists recognize that those stimuli which cause pain are liable to damage tissue. Accordingly, pain is that experience we associate with actual or potential tissue damage. It is unquestionably a sensation in a part or parts of the body, but it is also always unpleasant and therefore also an emotional experience. Experiences which resemble pain but are not unpleasant, e.g., pricking, should not be called pain. Unpleasant abnormal experiences (dysesthesias) may also be pain but are not necessarily so because, subjectively, they may not have the usual sensory qualities of pain. Many people report pain in the absence of tissue damage or any likely pathophysiological cause; usually this happens for psychological reasons. There is usually no way to distinguish their experience from that due to tissue damage if we take the subjective report. If they regard their experience as pain, and if they report it in the same ways as pain caused by tissue damage, it should be accepted as pain. This definition avoids tying pain to the stimulus. Activity induced in the nociceptor and nociceptive pathways by a noxious stimulus is not pain, which is always a psychological state, even though we may well appreciate that pain most often has a proximate physical cause.

The IASP definition is firmly anchored in both clinical practice and pain research, and even though it might be in need of an update [23], it is unlikely that it will be dramatically changed anytime in the near future. The definition mirrors a deeply seated conviction that pain, as being a “psychological state”, must always be respected as such. Such is the power of this definition that some authors have questioned the notion that one could even conceivably search for pain biomarkers [15]. According to this view, there is a logical contradiction (and an ethical danger) in the attempts to find objective biomarkers for subjective states like pain.

Let us now look more closely at the last sentence of the note to the IASP definition, which states that “activity induced in the nociceptor and nociceptive pathways by a noxious stimulus is not pain”. Here, the concepts of nociception and nociceptive pathways are contrasted to pain. According to IASP, nociception is “the neural process of encoding noxious stimuli”, and a noxious stimulus is “a stimulus that is damaging or threatens damage to normal tissues” [14]. Simply put, “encoding” here means that physical information is “transformed” into “electrical impulses” that quickly travel in a nerve towards the brain. Hence, nociception is something rather objective, and activity in the nociceptive pathways is (at least theoretically) measurable electrophysiologically [16].

The contrast between nociception and pain is important for pain researchers and pain physicians, and this distinction seems rather unique compared to other fields of medicine. For instance, there is to my knowledge no widespread term to denote activity in the optic nerve. I do not think ophthalmologists usually contrast vision with what we could perhaps could call “opticoception” (i.e., electrical activity in the optic nerve) in the way pain physicians differentiate between nociception and pain. I think this is for a good reason. There is something special about pain (and other bodily sensations) that has prompted the development of concepts that are not needed in ordinary perception. This will be discussed more below.

The biopsychosocial model has had a great impact on pain medicine [12]. In a widely influential paper published in Science in 1977, psychiatrist George L. Engel introduced the biopsychosocial model of health and disease [5, 11]. Engel argued that the prevailing biomedical model, based on reductive physicalism and mind-body dualism, had come to a dead end. Engel was not denying the overwhelming advances of modern medicine, but he thought there was a need for a more holistic reframing of medical science. He wrote that the doctor “must weigh the relative contributions of social and psychological as well as of biological factors implicated in the patient’s dysphoria and dysfunction as well as in his decision to accept or not accept patienthood and with it the responsibility to cooperate in his own health care” [11].

The biopsychosocial model fits well with the multifaceted view of pain implicit in the IASP definition. For instance, it is widely recognized that affective factors like fear [22] and depression [17] are important to assess in pain patients, although the causal relationships are complex and difficult to disentangle [17, 24]. The biopsychosocial model is consistent with the view of the brain as an active system that filters, selects and, through descending neural pathways, modulates nociceptive input from the periphery [18‐21].

Finally, it is important to contrast acute pain and chronic pain. Generally speaking, chronic pain, i.e. lasting for more than 3–6 months, is not meaningful in the sense that acute pain is. Chronic pain is often pain that has become a disease in its own right. In short: chronic pain can be thought of as a disease of the nociceptive system; the nociceptive system has become “over-reactive”. It has been suggested that the propensity of humans for chronic pain is a by-product of the high survival value of acute pain. According to this view, because the organism cannot afford missing life-threatening damage, the nervous system is biased in favour of pain sensitivity [8].

I do not think that chronic pain conditions should be the foundation of a philosophical analysis of pain. After all, if one wants to think about what vision is, does one start by analysing different disturbances in the vision field? Probably not. If I want to reflect on vision, I will probably not start by reflecting on glaucoma, cataract, or retinitis pigmentosa. Most probably, I will instead start by considering “normal” cases of vision, e.g., how should one philosophically analyse what happens when one sees an orange? Of course, a philosophical understanding of the meaning of vision must be integrated and congruent with an understanding of the pathologies of vision, but it seems to me that the fundamental understanding of vision is not predicated on how vision can be disturbed in different diseases. However, when philosophers reason about pain, they often start from cases of chronic pain. For instance, Aydede uses examples from phantom pain and referred pain [1]. This seems somewhat problematic to me. I think the first step when reflecting philosophically about pain is to analyse acute pain; introducing chronic pain at the outset risks confusing the picture too much. Once a solid philosophical understanding of acute pain has been gained, one could (and should) go on reasoning about the phenomenon of chronic pain (which can be thought of as acute pain gone awry).

First, let us clarify some basic concepts. Once again, Aydede shall be our guide. It is here important to distinguish between the concepts of introspection, interoception, and exteroception, and between two uses of the term perception. The distinctions are depicted in Fig. 1, which is based on [4]. In short, perception in the broad sense can be divided into (1) introspection (first-person access to one’s own mental states) and (2) perception in the narrow sense (epistemic access to something extra-mental). The latter can itself be divided into interoception (2a) and exteroception (2b). When Aydede talks about perception, he means the narrow sense, and I shall do the same. Perception, in the narrow sense, is epistemic access to something extra-mental; Aydede often uses the example of a red apple that one can see. As a contrast, introspection (not to be confused with interoception) is first-person access to one’s own mental state. Metaphorically speaking, in introspection I gaze deep down inside myself, whereas perception is outward-looking. At least, this is true for the kind of perception called exteroception. In interoception, I get epistemic access to something extra-mental which, however, is also something “inner”, a state of my body. If I have a chest pain, this is interoception-I get epistemic access to something that is “located” outside of my mind, but this is a particular form of perception, a perception which is about the state of my body, not something in the “outer world”. As we shall see below, I contend that there is a problematic duality at work here, but for the time being, the definitions and distinctions summarized in Fig. 1 will serve us well.

Murat Aydede is a very articulate proponent of a non-perceptual view of pain. In his 2009 paper, Aydede came to the conclusion that feeling pain is not perceiving something extramental [2]. According to him, pain is not an instance of ordinary perception, i.e., it is not “perception of one’s immediate extramental environment including one’s body” [3]. Pain is not seen as an instance of perception (in the narrow sense). Rather, pain is an example of introspection (see Fig. 1). In Aydede’s own words: “I think that PRT [perceptual/representational theory of pain] should be rejected: pain experiences are not perceptual” [4].

Of course, Aydede is not denying that the experience of pain is related to neural sensory mechanisms. In his own words, and using the above-mentioned term nociception:

Given the overwhelming neuroscientific evidence, it is foolish to deny that nociception is a genuine sensory modality. But this was not our question. Our question is rather whether the experiences this sensory modality helps to generate are genuinely perceptual. Perception requires some cognitive uptake or recognitional response to incoming sensory information: a merely sensory experience does not become perceptual until some sort of categorization can occur. [2].

Why does Aydede find a perceptual view of pain unconvincing? According to him, the main difficulty for a perceptual view of pain is what he calls the “asymmetry in concept application” for pain compared to e.g. vision [3]. When seeing something, we are not interested primarily in our own experience but in the thing that we actually see “out there”; the experience of seeing is (so to speak) transparent to the concept application—i.e., I can without problem apply the concept of the red apple that I see to the apple itself. Not so with pain. When experiencing pain, the experience itself takes centre-stage. Indeed, the very concept of pain is not applied to what causes the pain, but to the experience itself. A thorough discussion of Aydede’s views falls outside the scope of this paper (indeed, the present writer would not be able to do justice to his arguments); the interested reader is referred to Aydede’s own writings. Suffice it to say that, based on the “asymmetry in concept application”, Aydede makes a strong philosophical case against viewing pain as a form of perception.

However, it is also important to understand that even a perceptual view of pain does not entail a rejection of the subjectivity of the pain experience; what it does is to place pain on par with other sensory experiences like vision or hearing. As Aydede explains, for the perceptual theorist,

There may be philosophical problems about how privacy, subjectivity and incorrigibility are possible in a completely physical world, but if there are such problems, they are general problems about having perceptual experience of any kind, not necessarily pertaining to pains and other intransitive bodily sensations [3] (emphases added).

Hence, for the perceptual theorist, in that sense, there is nothing special about pain; pain has to do with the perception of tissue damage. What is special with pain, the perceptual theorist acknowledges, is that the application of the concept is odd: it is applied not to tissue damage itself, but to the subjective experience. Compared to e.g. vision, there is what Aydede calls an “asymmetry in concept application” for pain [3]. Nonetheless, according to perceptual theorists, the flow of information being the same in pain and vision, both are instances of perception. However, as we have seen, Aydede does not agree.

I concur with Aydede that there is something peculiar with pain and other bodily sensations-a peculiarity that might justify the rejection of pain as the perception of something. However, I think that the peculiarity of pain, and the problems many theorists (including Aydede) encounter when reflecting upon pain, might (at least in part) be due to an entrenched and deeply problematic dualism between the mental and the extra-mental. I propose that exposing this problematic duality, and replacing it by another (in my opinion) more defensible duality, would clarify the issues at stake. Given this more defensible duality, pain could be viewed not as the perception of something, but of someone—namely, the self.

I contend that Aydede’s writings unveil a problematic dichotomy between the categories of the mental and of the extra-mental. This dichotomy seems rather self-evident to him, and it permeates the papers I have read. The mental versus extra-mental dichotomy seems to be grounded in the preponderance given to the brain as over the body as a whole. Hence, what takes place in the body (presumably with the exception of the brain) is “extra-mental”, and it is from that point of view that the concept of interoception is understood. Remember that, according to the distinctions depicted in Fig. 1, interoception is a form of perception–perception being defined as epistemic access to something extra-mental. Hence, the dichotomy between mental and extra-mental is the lens through which the distinctions of Fig. 1are understood. When for instance Aydede writes about “one’s body parts” [2, p. 538], the dichotomy is at work; an alternative wording would have been “in parts of the body”. Another example is when he writes about the view according to which”perception is essentially an activity of gathering information about one’s immediate external environment, that is, environment external to one’s mind and experiences, where this environment involves one’s body or events internal to one’s body” [1, p. 15]. Here, Aydede seems to be saying that one’s body is part of the “external environment”!

This mental versus extra-mental dichotomy seems unsatisfactory. Instead of arguing against it at length, I will here propose an alternative, replacing the twin concepts of exteroception and interoception by what I will call cosmoception and egoception. The basic dichotomy is hence no longer the mental/extra-mental but the distinction between world and body. The difference may seem small, but it seems to me that it is profound.

Cosmoception (from cosmos, “world” in Greek) is, broadly speaking, equivalent to exteroception. In cosmoception, I gain epistemic access to something “outside of me”. When I see a red apple on the table, I get epistemic access to precisely that objective fact (George Berkeley notwithstanding). Egoception (from ego, “I” in Greek), on the other hand, corresponds broadly to interoception. Egoception includes the skin and other visible parts of the body, hence also parts of the body that are not “on the inside”. Indeed, the term interoception seems to imply that it has to do with what happens on the inside, “under the skin”. But my skin is also me. And when my skin is damaged, I get epistemic access to that through pain/egoception. Cosmoception is about the world outside my body; egoception is about my body, it is about the self, it is about me and my place in the world, about how the world affects the body that is I.

These two neologisms have the advantage of not pushing our thought into a mental/extra-mental or an inner/outer dichotomy. Of course, the contrast between cosmoception and egoception is itself a dichotomy, but it seems to me to be a much fruitful one in its anti-cartesianism. It goes without saying that I’m not denying that some phenomena can be described as mental, whereas others are extra-mental. But when the mental/extra-mental dichotomy is given preponderance over the dichotomy between body and world, problems arise when reflecting over pain (as I propose can be seen in the writings of Aydede).

Of course, there are similarities between the experience of sharpness and the experience of pain, as in both cases action potentials travel in neurons from the periphery to the brain. But the experience is different, the locus of attention being the world or the self, cosmoception or egoception. The body that is me is not an object among other objects in the world, it is my perspective on the world. When I feel that a candle flame is warm, I get epistemic access to something that is happening in the world. If I approach my hand to much, I will feel pain, because I now feel that my body is dangerously affected.²

I think that the “asymmetry in concept application”, which is central to Aydede’s thinking here, forces him into a non-perceptual view of pain precisely because he reasons from the perspective of mental/extra-mental. When viewed from a body/world perspective, however, there is arguably nothing strange about the “asymmetry in concept application”. On the contrary, it is to be expected. Pain having to do with egoception, the concept will be applied not to the world “out there” but to myself. The key, it seems to me, is to leave the mental/extra-mental perspective and instead view pain from a body/world perspective.