First-Person Neuroscience of Pain: Puzzles, Methods and Data

First-Person Neuroscience of Pain: Puzzles, Methods and Data from simonvanrysewyk

Challenges facing pain reductionism

The official scientific definition of pain was initially formulated in the 1980s by a committee organized by the International Association for the Study of Pain (IASP). This definition and accompanying Note was updated in the 1990s by the IASP to reflect advancements in pain science and has since been widely accepted by the scientific community:

Pain: An unpleasant sensory and emotional experience associated with actual or potential tissue damage, or described in terms of such damage.

Note: 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 (IASP-Task-Force-On-Taxonomy, 1994: 207-213).

An apparent immediate and inconvenient fact facing pain reductionism is that pain stubbornly resists identification with only the brain. The original pain identity statement proposed by philosopher U.T. Place, ‘Pain = C-fibre activation’ (Place, 1956), neglects two essential features of pain observed in contemporary pain science:
(1) Conscious awareness of wounding is multimodal and is correlated with integrated visual, kinaesthetic, and enteric sensory modalities in addition to noxious signalling (e.g., Chapman et al. 2008);
(2) Wounding is typically part of overall bodily awareness that is correlated with multiple reciprocal nervous, endocrine and immune states (e.g., Chapman et al. 2008; Lyon et al. 2011; van Rysewyk, 2013; Vierck et al. 2010). Convergent lines of evidence demonstrate that wounding followed by pain is strongly correlated with endocrine and immune operations as well as sensory signaling that together exert an extensive non-neural impact. These operations interact and comprise a defensive stress response to wounding [1].

A consideration of the higher structures of the central nervous system (CNS) alone reveals an extraordinarily complex picture of pain. Unimodal functional brain imaging studies of nociceptive transmission, projection and processing show that signals of wounding reach higher CNS levels via the spinothalamic, spinohypothalamic, spinoreticularpathways (i.e., the paleospinothalamic tract) including the locus caeruleus (LC) and the solitary nucleus, spinopontoamygdaloid pathways, the periaqueductal gray (PAG), and the cerebellum (e.g., Burstein et al. 1991; Price, 2000). The thalamus (THA) projects to limbic areas including the insula and anterior cingulate, which have been identified with the integration of the emotional and motivational features of pain (Craig, 2002, 2003a, 2003b). Noradrenergic pathways from the LC project to these and other limbic structures. Accordingly, pain reveals extensive limbic, prefrontal and somatosensory cortical components. A meta-analysis of the literature described brain operations during pain as a complex network involving THA, primary and secondary somatosensory cortices (S1, S2), insula (INS), anterior cingulate (ACC), and prefrontal cortices (Apkarian et al. 2005). Thus, the brain engages in massive, distributed, parallel processing in response to noxious signaling.

The mechanisms of multimodal integration pose a formidable challenge for pain scientists. Hollis et al. (2004) examined how catecholaminergic neurons in the solitary nucleus integrate visceral and somatosensory information when peripheral inflammation is present. Pre-existing fatigue, nausea, intense physiological arousal, and a systemic inflammatory response induced by proinflammatory cytokines (e.g., Anderson, 2005; Eskandari et al. 2003) are all correlated with sensory signalling in the experience of pain. In addition to Craig (2002, 2003a, 2003b), an increasing number of studies have investigated the integration of information from multiple sensory modalities and central operations correlated with emotion and cognition in pain (e.g., Bie et al. 2011; Liu et al. 2011; Neugebauer et al. 2009). The more we are able to delineate the qualia of pain and map these experiences onto specific multimodal physical operations, the closer we come to identifying pain with those operations.

So, why has Place’s (1956) original pain identity statement survived in philosophy of mind? One reason is that the use of ‘C-fibre activation’ by identity philosophers is merely a placeholder for whatever the eventual mechanisms of nervous systems prove to be. We now know that wounding is identical to specific endocrine and immune operations in addition to sensory signaling. These operations interact and in concert comprise a defensive stress response to wounding. However, the purpose of calling it the identity theory of mind is to separate it from philosophical theories that identify mental states with states of immaterial souls or minds (dualism), abstract machine systems (functionalism), or those theories that reject the reality of mental states (eliminativism). It is not to make any substantive assumption about the sensory modality. This is why Place’s (1956) pain identity claim of C-fibre activation has survived, despite being explanatorily incomplete.

[1] In clinical settings, problems of acute and chronic pain do not easily conform to pain-brain type identities. The persistence of chronic pain as a major problem in medicine may indicate that identifying pain with the brain (‘pain in the brain’) has failed to inform clinicians toward curative interventions (e.g., Chapman et al. 2008).

References
Anderson, J. (2005). The inflammatory reflex-introduction. Journal of Internal Medicine, 257(2), 122-125.
Apkarian, A. V., Bushnell, M. C., Treede, R. D., & Zubieta, J. K. (2005). Human brain mechanisms of pain perception and regulation in health and disease. European Journal of Pain, 9(4), 463-463.
Bie, B., Brown, D. L., & Naguib, M. (2011). Synaptic plasticity and pain aversion. European Journal of Pharmacology, 667(1), 26-31.
Burstein, R., Dado, R. J., Cliffer, K. D., & Giesler, G. J. (1991). Physiological characterization of spinohypothalamic tract neurons in the lumbar enlargement of rats. Journal of Neurophysiology, 66(1), 261-284.
Chapman, C. R., Tuckett, R. P., & Song, C. W. (2008). Pain and stress in a systems perspective: reciprocal neural, endocrine, and immune interactions. The Journal of Pain, 9(2), 122-145.
Craig, A. D. (2002). How do you feel? Interoception: the sense of the physiological condition of the body. Nature Reviews Neuroscience, 3(8), 655-666.
Craig, A. D. (2003a). A new view of pain as a homeostatic emotion. Trends in Neurosciences, 26(6), 303-307.
Craig, A. D. (2003b). Pain mechanisms: labeled lines versus convergence in central processing. Annual Review of Neuroscience, 26, 1-30.
Eskandari, F., Webster, J. I., & Sternberg, E. M. (2003). Neural immune pathways and their connection to inflammatory diseases. Arthritis Research and Therapy, 5(6), 251-265.
IASP-Task-Force-On-Taxonomy (1994). IASP Pain Terminology. In H. Merskey & N. Bogduk (Eds.), Classification of Chronic Pain: Descriptions of Chronic Pain Syndromes and Definitions of Pain Terms (pp. 209-214). Seattle: IASP Press.
Liu, C. C., Shi, C. Q., Franaszczuk, P. J., Crone, N. E., Schretlen, D., Ohara, S., & Lenz, F. A. (2011). Painful laser stimuli induce directed functional interactions within and between the human amygdala and hippocampus. Neuroscience, 178, 208-217.
Lyon, P., Cohen, M., & Quintner, J. (2011). An Evolutionary Stress‐Response Hypothesis for Chronic Widespread Pain (Fibromyalgia Syndrome). Pain Medicine, 12(8), 1167-1178.
Neugebauer, V., Galhardo, V., Maione, S., & Mackey, S. C. (2009). Forebrain pain mechanisms. Brain Research Reviews, 60(1), 226.
Place, U. T. (1956). Is consciousness a brain process? British Journal of Psychology, 47, 44-50.
Price, D. D. (2000). Psychological and neural mechanisms of the affective dimension of pain. Science, 288(5472), 1769-1772.
van Rysewyk, S. (2013). Pain is Mechanism. Doctoral Dissertation, University of Tasmania.
Vierck, C. J., Green, M., & Yezierski, R. P. (2010). Pain as a stressor: effects of prior nociceptive stimulation on escape responding of rats to thermal stimulation. European Journal of Pain, 14(1), 11-16.

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Critique of Max Velmans on mind-brain identity theory and consciousness – part I

In this first post of a series, I describe and challenge several criticisms of reductive materialism, or mind-brain identity theory [5,6,7,8,9,10], made by psychologist Max Velmans. My focus in this post concerns Velmans’s arguments against mind-brain identity theory as presented in ‘What non-eliminative materialism needs to show’ in Appendix I of [4]. Future posts will address his other arguments against mind-brain identity theory as presented in the same work. My intention here is not simply negative, but also positive: using the first-person third-person distinction Velmans appeals to, I propose that the first-person point of view (introspection) and first-person methods are necessary to consciousness science. In developing this view, I focus mostly on pain.

Velmans is a long-time critic of materialist theories of phenomenal consciousness [1,2,3,4]. Following philosopher CD Broad, Velmans distinguishes three versions of materialism: radical, reductive and emergent. He writes [4]:

Radical materialism claims that the term “consciousness” does not refer to anything real (in contemporary philosophy this position is usually called “eliminativism”). Reductive materialism accepts that consciousness does refer to something real, but science will discover that real thing to be nothing more than a state (or function) of the brain. Emergentism also accepts the reality of consciousness but claims it to be a higher-order property of brains; it supervenes on neural activity, but cannot be reduced to it. [4,20]

Velmans begins his argument against mind-body identity theory:

Let us assume that, in some sense, our conscious experiences are real. To each and every one of us, our conscious experiences are observable phenomena (psychological data) which we can describe with varying degrees of accuracy in ordinary language. Other people’s experiences might be hypothetical constructs, as we cannot observe their experiences in the direct way that we can observe our own, but that does not make our own experiences similarly hypothetical. Nor are our own conscious experiences “theories” or “folk psychologies.” We may have everyday theories about what we experience, and with deeper insight, we might be able to improve them, but this would not replace, or necessarily improve the experiences themselves. [4,20-21]

In this passage, Velmans denies that our conscious experiences are ‘theories’ or ‘folk psychologies.’ However, since that is a central claim made by radical materialism (‘eliminativism’) [5,6], not reductive materialism (mind-brain identity theory), Velmans is in error to attribute it to the latter. Like mind-brain identity theory, eliminativism accepts the claim that conscious states are ‘nothing over and above’ brain states (minimal reductionism), but it rejects type identity. This is because eliminativism denies that conscious states are real, and do not exist [10]. By contrast, mind-brain identity theory is realist about mental states and experiences [10]. Mind-brain identity theory is not equivalent to eliminativism [10] (1).

The final sentence in the quote above reads: ‘We may have everyday theories about what we experience, and with deeper insight, we might be able to improve them, but this would not replace, or necessarily improve the experiences themselves.'[my italics] Critics of mind-brain identity theory, like Velmans, believe that a successful scientific reduction of consciousness would make all conscious experiences somehow unreal or even disappear [e.g., 17,18]. Using this conception of reduction, it is then reasoned that because it is observably obvious that a conscious experience like pain is real, it cannot be reduced by science to neurobiological mechanism. This misunderstanding trades on a peculiar view of reduction, where it is expected that in science, type identity claims make conscious experiences disappear. I think this expectation is incorrect.

Temperature was ontologically reduced to mean molecular kinetic energy, but no person expects that temperature therefore ceased to be real or became scientifically disrespectable or redundant. Visible light was ontologically reduced to electromagnetic radiation, but light did not disappear. Instead, scientists understand more about the real nature of light than they did before 1873. Light is real, no doubt; and so is temperature. Some expectations about the nature of temperature and light did change, and scientific progress does occasionally require rethinking what was believed about phenomenon. In certain instances, previously respectable states and substances sometimes did prove to be unreal. The caloric theory of heat did not survive rigorous experimental testing; caloric fluid thus proved to be unreal. Thus, a successful type identity of pain with mechanism means only that there is an explanation of pain. It is a reduction. But, scientific explanations of phenomenon do not typically make them disappear [5,6,10].

Velmans continues his argument:

In essence then, the claim that conscious experiences are nothing more than brain states is a claim about one set of phenomena (first-person experiences of love, hate, the smell of mown grass, the colour of a sunset, etc.) being nothing more than another set of phenomena (brain states, viewed from the perspective of an external observer). Given the extensive, apparent differences between conscious experiences and brain states this is a tall order. [4,21]

By characterizing mind-brain identity theory as a ‘tall order’, Velmans is in danger of begging the question. It is possible that science will never understand how brain structures such as neurons and protein channels produce pains, emotions and thoughts. The reality of the brain may be forever closed to us. Still, that the problem of consciousness is scientifically tractable or intractable, solvable or insolvable, is impossible to tell simply by noting appearances, since problems do not rank level of difficulty on their sleeves. Why should the problem of consciousness be any different?

Besides, things change. Over time, the nature of a problem may alter shape as new knowledge and understanding arrive. A problem may come to be viewed in novel ways as a result of reciprocal developments in technology, scientific methods and theory. For example, the composition of stars was regarded by scientists as an intractable problem. The problem was that it was impossible to get close enough to collect a star sample without burning up. However, with the unexpected discovery of spectral analysis, this problem proved tractable. The elements of stars were found to produce a type of fingerprint when heated to incandescence, easily observed when light produced from a source is passed through a prism.

In the early twentieth century, the copying problem in molecular genetics was thought to be intractable. This problem, however, was solved in the decades following Watson and Crick’s 1953 publication that DNA is a double helix. By contrast, the problem of how protein molecules fold into their 3D shape once made, believed by many scientists to be solvable in the mid-twentieth century, remains entirely unsolved today despite many decades of effort. Moreover, contributing solutions to twenty-first century problems can come from surprising and novel sources that may challenge conventional thinking. What seems apparently true or observably obvious during immediate experience or armchair reflection is sometimes a poor guide to reality.

Velmans again:

Instances where phenomena viewed from one perspective turned out to be one and the same as seemingly different phenomena viewed from another perspective do occur in the history of science. A classical example is the way the “morning star” and the “evening star” turned out to be identical (they were both found to be the planet Venus). But viewing consciousness from a first- versus a third-person perspective is very different to seeing the same planet in the morning or the evening. From a third-person (external observer’s) perspective one has no direct access to a subject’s conscious experience. Consequently, one has no third-person data (about the experience itself) which can be compared to or contrasted with the subject’s first-person data. [4,21]

It is unclear what Velmans means by ‘From a third-person (external observer’s) perspective one has no direct access to a subject’s conscious experience.’ I presume he intends that what I experience during a conscious episode cannot be available to you or indeed any one else in the way it is directly available to me. I occupy a uniquely privileged position concerning my experience that no one else can occupy. But if so, then he is intuitively characterizing the problem of consciousness in terms of method of access, and in terms of a privileged mode of access at that, namely, ‘direct’ personal introspection, which is question-begging.

This intuitive take on the problem of consciousness also results in a misrepresentation of what science is really up to, since the scientific enterprise relies on the intersubjective availability of its subject matter, in that no one is privileged with regard to collecting evidence about the object of the study. This means that no one has any special epistemic authority over evidence that others cannot in principle understand. In principle, must a successful reduction of pain produce a scientific explanation and pain? Obviously, no – scientific pain research aims to explain pain; it is not in the business of spontaneously concocting the phenomenon in question. To think otherwise is to misrepresent the limits and possibilities of science [5,6,10].

Now, there is a positive characterization of Velmans’s appeal to the first-person and third-person distinction I wish to show. Velmans’s description of the consciousness landscape should be taken to imply that the subject matter of consciousness research is brain mechanism as related to conscious phenomena. For example, the subject of pain science is brain mechanism as related to pain phenomena (e.g., acute pain, chronic pain, fetal pain, empathy for pain, dreamed pain, near-death pain, and so on). Consciousness research aims to discover the brain mechanisms subserving conscious experiences accessible only through introspection, which means that consciousness research is entirely reliant on the first-person point of view and on using first-person investigative methods. Contrary to Velmans’s view, this necessarily includes introspection together with third-person methods (e.g., neuroimaging). Since consciousness research aims to know which experience types are generated by which brain mechanism, researchers must naturally know when specific conscious experiences occur and what their personal qualities are. Which means that introspection is indispensable to consciousness research.

The history of scientific pain research clearly shows that introspection has been extensively used. For example, pain psychophysics typically uses subject pain verbal-report or non-verbal behavior (e.g., facial expressions) to infer the presence of pain. That is, pain psychophysics is committed to subject introspection. It is also important to remember that the validity of pain-related neuroimaging was established by the correlation of brain images with self-report of pain [19].

Finally, Velmans:

Neurophysiological investigations are limited, in principle, to isolating the neural correlates or antecedent causes of given experiences. This would be a major scientific advance. But what would it tell us about the nature of consciousness itself? [4,21]

I will respond to Velmans’s question with my own: how is mind-brain identity theory positioned relative to the indispensability of introspection to consciousness research? As Velmans notes, introspection is a direct way of coming to know about personal experiences and their qualities. It is an epistemological activity. Still, despite appearances to the contrary or personal conviction, what introspection reveals to us may be utterly mechanistic. It may be that what neuroscientists study through third-person methods is type identical with what is personally experienced through introspection, that is, brain mechanisms of the appropriate type. There is only one type of activity in question: the brain mechanism with all and only physical properties.

Mind-brain identity theory follows a long line of identifications that have marked progress in knowledge: water is H2O, light is electromagnetic energy, lightning is electrical discharge, influenza is a viral infection, and so on. Each of these identities is part of a larger theory that was accepted because it provided a better explanation of the evidence than rival theories. To illustrate this claim, take the conventional example of the type identity of fire and rapid oxidation. Why is this type identification descriptive (i.e., informative)? The first step is to conduct a qualitative investigation of fire. The flame is the visible part of fire, it releases heat and light, is normally sustained by a continuous supply of fuel, and so on. Some qualitative facts about fire are easily observed and others take further investigation, for instance, facts about the reactions that make fire explode. This provides a provisional description of fire. These qualitative descriptions (facts) about fire are then matched with qualitative descriptions (facts) about the operation of rapid oxidation, which is the sequence of chemical reactions between a fuel and an oxidant, such as oxygen or fluorine gas. These facts are harder to describe but essential. When sufficient information is at hand concerning the parts and operations of fire and the parts and operations of specific chemical reactions (rapid oxidation), we can describe how the structure of fire delineates its qualitative chemical properties. The multilevel mechanistic description of fire type identifies it with a specific mechanism type, rapid oxidation, and describes its behavior in terms of the behavior and composition of this mechanical operation. Fire is rapid oxidation.

The type identification of fire and rapid oxidation is only enabled if other substances are also type identified with other molecules, and if elements are type identified with chemical types, and so on. That is, the type identity of fire and rapid oxidation works because it is framed in the broader descriptive context of chemistry and physics. Those general framework theories imply the type identifications. Of course, the type identification of fire and rapid oxidation might be faulted as an incorrect description, perhaps because the physical operations involve activity in a broader range of physical processes. But that criticism merely asserts a different type identity description, and does not challenge type identity claims per se. It is conceivable to ponder whether fire is correctly type identified with rapid oxidation rather than with some other operation; but within the framework of chemistry and physics as they are understood, it is not reasonable to ponder whether fire might fail to be any type of mechanical operation at all.

In the same way, mind-brain identity theory is part of a rich theory that aims to explain conscious and unconscious mental phenomena such as perception, memory, reasoning, addiction, and disease. The personal experience of pain is multidimensional and involves specific sensory, emotional and cognitive features. I think there is a well established multilevel view of the physiological mechanisms that best describes pain qualities. This mechanistic description is framed within the context of advancing theories of the nervous, endocrine and immune systems and their complex functional interdependencies. There are also complex adaptive system-based descriptions of pain experience. Taken together, these descriptions reveal how pain is type identified with mechanism [10].

Although empirical progress in the understanding of pain is typically gradual and piecemeal, the type identification of pain with brain mechanism does not proceed in an additive manner. Pain scientists do not discover one pain type identity at a time and then add them together. Rather, what justifies claims to have type identified the mechanisms of pain is the way the entire multilevel mechanistic package coheres [10].

Endnotes

1. Briefly, the central argument for eliminativism is the idea that we use a theoretical framework to explain and predict human behavior [11], usually called the theory-theory (TT). TT views folk psychology (FP) as comprising specific theoretical claims and generalizations (and laws), described by our everyday common-sense psychological (i.e., mental) words such as ‘belief’, ‘desire’, ‘recognition’, ‘fear’, ‘anticipate’, ‘memory’ or ‘pain’. FP generalizations are thought to describe the diverse causal regularities and relations of FP claims.

TT claims that FP generalizations and claims operate in FP much like the generalizations and laws of scientific theories. However, the laws of FP are acquired more informally than scientific theories, as part of normal human development [e.g., 12,13,14,15]. For example, children who observe their parents showing fear and behavioral avoidance to back-stressing tasks, such as lifting heavy objects, may adjust their understanding of that situation (‘back-stressing tasks are dangerous and can cause pain’) and the behavioral effects (‘avoidance of back-stressing tasks generally reduces pain’) based on the generalization ‘Since back-stressing tasks can cause pain, and avoidance of these tasks generally reduces pain, it is best to avoid such tasks’ [16].

References

[1] Velmans, M. (2000). Understanding Consciousness. London: Routledge/Psychology Press.

[2] Velmans M. (2001a). A natural account of phenomenal consciousness. Consciousness and Communication, 34(1&2), 39-59.

[3] Velmans M. (2001b). Heterophenomenology versus critical phenomenology: A dialogue with Dan Dennett. http://cogprints.soton.ac.uk/documents/disk0/00/00/17/95/index.html.

[4] Velmans M. (2002). How Could Conscious Experiences Affect Brains? Journal of Consciousness Studies 9(11), 3-29.

[5] Churchland PM. (2007). Neurophilosophy at work. Cambridge, UK: Cambridge University Press.

[6] Churchland PS. (1989). Neurophilosophy: Toward a unified science of the mind-brain. Cambridge, Mass.: The MIT Press.

[7] Place UT. (1956). Is Consciousness a Brain Process? British Journal of Psychology, 47, 44-50.

[8] Polger TW. (2004). Natural minds. Cambridge, Mass.: The MIT Press.

[9] Smart JJC. (1959).  Sensations and Brain Processes. Philosophical Review, 68, 141-156.

[10] van Rysewyk S. (2013). Pain is Mechanism. PhD Dissertation, University of Tasmania.

[11] Sellars W. (1956). Empiricism and the Philosophy of Mind. Minnesota Studies in Philosophy of Science, 1, 253-329.

[12] Churchland PM. (1981). Eliminative Materialism and the Propositional Attitudes. Journal of Philosophy, 78, 67-90.

[13] Hardcastle VG. (1999). The Myth of Pain. Cambridge, Mass.: MIT Press.

[14] Roth M. (2012). Folk psychology as science. Synthese, 189(4), 1-12.

[15] Stich S. (1983). From Folk Psychology to Cognitive Science. Cambridge Mass.: MIT Press.

[16] Goubert L, Vlaeyen JW, Crombez G, & Craig KD. (2011). Learning about pain from others: an observational learning account. The Journal of Pain, 12(2), 167-174.

[17] Chalmers D. (1996). The Conscious Mind. Oxford: Oxford University Press.

[18] Searle JR. (1992). The Rediscovery of Mind. Cambridge, Mass.: MIT Press.

[19] Coghill RC, McHaffie JG, Yen YF. (2003). Neural correlates of interindividual differences in the subjective experience of pain. Proceedings of the National Academy of Science USA, 100, 8538-8542.