Is pain where you feel it in the body, or in the brain? Neurophenomenology and the spatial aspect of nociception

Pain is interesting, salient, mysterious. It may feel like it is in one specific place in or on the body. It may feel diffuse, with gradations, or it may seem referred from one area to another. What is happening in the brain and in the body as these spatial aspects of pain are experienced? How much of the causation of pain occurs where we feel it, and how much occurs in the brain? Below is a series of probes and thinking aloud about where pain is, with speculations to stimulate my thinking and yours.  I’m not a “pain expert”, nor a bodyworker that heals clients, nor a physiologist with a specialization in nociception, but a cognitive scientist, with clinical psychology training, interested in body phenomenology and the brain.  Please do post this essay to Facebook, share it, critique, respond, and comment (and it would be helpful to know if your background is in philosophy, neuroscience, bodywork, psychology, medicine, a student wanting to enter one of these or another field, etc). Pain should be looked at from multiple angles, with theoretical problems emphasized alongside clinical praxis, and with reductionistic accounts from neurophysiology juxtaposed against descriptions of the embodied phenomenology and existential structures.  As I have mentioned elsewhere, it is still early in the history of neurophenomenology…let a thousand flowers bloom when looking at pain. We need data, observations, insights and theories from both the experience side as well as the brain side. Francisco Varela aptly described how phenomenology and cognitive neuroscience should relate:

“The key point here is that by emphasizing a codetermination of both accounts one can explore the bridges, challenges, insights, and contradications between them. Both domains of phenomena have equal status in demanding full attention and respect for their specificity.”

We all know what pain is phenomenologically, what it feels like, but how to define it? The International Association for the Study of Pain offers this definition: “an unpleasant sensory and emotional experience associated with actual or potential tissue damage, or described in terms of such damage.” Of particular interest to neurophenomenology and embodied cognitive science is their claim that “activity induced in the nociceptors and nociceptive pathways by a noxious stimulus is not pain, which is always a psychological state.” Good that they do not try to reduce the experience of pain to the strictly physiological dimension, but I wonder how Merleau-Ponty, with his non-dualistic ontology of the flesh would have responded. Pain seems to transgress the border of mind and body categories, does it not? I am slowly biting off chucks of the work on pain at the Stanford Encyclopedia of Philosophy. Lots of provocative angles, including this one:

“there appear to be reasons both for thinking that pains (along with other similar bodily sensations) are physical objects or conditions that we perceive in body parts, and for thinking that they are not. This paradox is one of the main reasons why philosophers are especially interested in pain.”

Right now I am particularly interested in the spatial aspect of where pain seems to be, what I might label the spatial phenomenology of nociception. When I introspect on aching parts of my feet, it seems as if the pain occupies a volume of space. Using manual pressure I can find places on my feel that are not sore, right next to areas that are slightly sore, which are in turn near focal areas of highest pain. It seems as if the pain is locatable “down there” in my body, and yet what we know about the nociceptive neural networks suggests the phenomenology is produced by complex interactions between flesh, nearby peripheral nerves, the central nervous system, and neurodynamics in the latter especially. A way of probing this this would be to examine the idea that the pain experience is the experiential correlate of bodily harm, a sort of map relating sensations to a corresponding nerve activated by damage to tissue. So, is the place in my body where I feel pain just the same as where the damage or strain is? Or, Is pain caused by pain-receptive nerves registering what is happening around them, via hormonal and electrical signals? Or is pain actually the nerve itself being “trapped” or damaged, yet in a volume of undamaged tissue one can feel hurts? Could the seeming volume of experienced pain-space be a partial illusion, produced by cognizing the tissue damage as some place near or overlapping with yet not spatially identical to where the “actual” damage is, in other words a case of existential-physiological discrepancy? One scenario could be, roughly, that pain “is” or “is made of” nerves getting signals about damage to tissue; another would be that pain “is” the nerves themselves being damaged or sustaining stress or injury. Maybe pain involves both? Maybe some pain is one, or the other? In terms of remembering how my heel pain started, it’s not so easy, but I love to walk an hour or two a day, and have done so for many years. I recall more than ten years ago playing football in the park, wearing what must have been the wrong sort of shoes, and upon waking the next day, having pretty serious pain in my heel. Here are some graphics that, intuitively, seem to map on to the areas where I perceive the pain to be most focal:

from bestfootdoc.com

from setup.tristatehand.com

from plantar-fasciitis-elrofeet.com

If I palpate my heel, I become aware of a phenomenologically complex, rich blend of pleasure and pain. I crave the sensation of pressure there, but it can be an endurance test when it happens. Does the sensation of pressure that I want reflect some body knowledge, some intuitive sense of what intervention will help my body heal? How could this be verified or falsified? It is not easy to describe the raw qualia of pain, actually. I can describe it as achey and moderately distressing when I walk around, and sharp upon palpating. Direct and forceful pressure on the heel area will make me wince, catch my breath, want to gasp or make sounds of pain/pleasure, and in general puts me in a state of heightened activation. But I love it when I can get a therapist to squeeze on it, producing what I call “pain-pleasure”:

from indyheelpaincenter.com

This diagram below helps me map the sensations to the neuroanatomy. We need to do more of this sort of thing. This kind of representation seems to me a new area for clinical neurophenomenological research (indeed, clinical neurophenomenology in general needs much more work, searching for those terms just leads back to my site, but see the Case History section in Sean Gallagher’s How the Body Shapes the Mind).

from reconstructivefootcaredoc.com

What is producing the pain-qualia, the particular feeling? Without going too far into varying differential diagnosis, it is commonly attributed to plantar fasciitis.  There the pain would be due to nociceptive nerve fibers activated by damage to the tough, fibrous fascia that attach to the calcaneus (heel bone) being strained, or sustaining small ripped areas, and/or local nerves being compressed or trapped. A 2012 article in Lower Extremity Review states that “evidence suggests plantar fasciitis is a noninflammatory degenerative condition in the plantar fascia caused by repetitive microtears at the medial tubercle of the calcaneus.” There are quite a few opinions out there about the role of bony calcium buildups, strain from leg muscles, specific trapped nerves and so forth, and it would be interesting to find out how different aspects of reported pain qualia map on to these. Below you can see the sheetlike fascia fiber, the posterior tibial nerve, and it’s branches that enable local sensations:

from aafp.org

Next: fascia and the innervation of the heel, from below:

from mollyjudge.com

Another view of the heel and innervation:

from mollyjudge.com

Below is a representation of the fascia under the skin:

from drwolgin.com

There is a very graphic,under the skin, maybe not SFW surgeon’s-eye perspective on these structures available here. Heel pain turns out to be very common, and is evidently one of the most frequently reported medical issues. Searching online for heel pain mapping brings up a representation purportedly of 2666 patients describing where they feel heel pain: I can’t find where this comes from originally and can’t speak to the methodology, rigor, or quality of the study, but the supposed data are interesting, as is the implicit idea of spatial qualia mapping:  the correspondence of experienced pain to a volume of space in the body. It also quite well represents where the pain is that I feel. The focal area seems to be where the fascia fibers attach to the calcaneus, an area that bears alot of weight, does alot of work, and is prone to overuse. So, where is the pain? Is it in the heel or the brain? Is it in the tissue, the nerve, or both? Is there a volume of flesh that contains the pain? I am going to have to think about these more, and welcome your input. What about the central nervous system that processes nociceptive afferents coming from the body? A good model of pain neurophenomenology should involve a number of cortical and subcortical areas that comprise the nociceptive neural network: -primary somatosensory cortex (S1) and secondary somatosensory cortex (S2): -insula -anterior cingulate cortex (ACC) -prefrontal cortex (PFC) -thalamus Here are some representations of the pain pathways, or the nociceptive neural network:

from Moisset and Bouhassira (2007)

Moisett el (2009)

 

from Tracey and Mantyh (2012)

Broadly speaking, pain seems to be generated by tissue damage, inflammation, compromising the integrity of tissue, stress on localized regions, and so forth being processed by peripheral afferent pain pathways in the body, then phylogenetically ancient subcortical structures, and then the aforementioned cortical regions or nociceptive neural network.  As I have mentioned many times, making a robust account of how various regions of the brain communicate such that a person experiences qualia or sensory phenomenology will need to reference neurodynamics, which integrates ideas from the physics of self-organization, complexity, chaos and non-linear dynamics into biology.  It is gradually becoming apparent to many if not most workers in the cognitive neurosciences that there are a host of mechanisms regions of the brain use to send signals, and many of these are as time dependent as space dependent. Michael Cohen puts it thusly: “The way we as cognitive neuroscientists typically link dynamics of the brain to dynamics of behavior is by correlating increases or decreases of some measure of brain activity with the cognitive or emotional state we hope the subject is experiencing at the time. The primary dependent measure in the majority of these studies is whether the average amount of activity – measured through spiking, event-related-potential or -field component amplitude, blood flow response, light scatter, etc. – in a region of the brain goes up or down. In this approach, the aim is to reduce this complex and enigmatic neural information processing system to two dimensions: Space and activation (up/down). The implicit assumption is that cognitive processes can be localized to specific regions of the brain, can be measured by an increase in average activity levels, and in different experimental conditions, either operate or do not. It is naïve to think that these two dimensions are sufficient for characterizing neurocognitive function. The range and flexibility of cognitive, emotional, perceptual, and other mental processes is huge, and the scale of typical functional localization claims – on the order of several cubic centimeters – is large compared to the number of cells with unique physiological, neurochemical, morphological, and connectional properties contained in each MRI voxel. Further, there are no one-to-one mappings between cognitive processes and brain regions: Different cognitive processes can activate the same brain region, and activation of several brain regions can be associated with single cognitive processes. In the analogy of Plato’s cave, our current approach to understanding the biological foundations of cognition is like looking at shadows cast on a region of the wall of the cave without observing how they change dynamically over time.” But what of the original question? Is pain where you feel it in the body, or in the brain? It seems to me the answer must be both.  The experience of pain being localized there or a little on the left is a product of local tissue signals and receptor activation, which produces peripheral afferent nerve firing, which gets processed by spinal afferent neurodynamics, brainstem activation, thalamic gating, and then somatosensory, insular, anterior cingulated, and prefrontal cortical regions. Yet the real model of pain, one that invokes mechanisms and causes, remains elusive. And a good model of pain must account for the possibility of pain without suffering as well! For now, what I can offer are probes to get us speculating, thinking critically, and eventually building a clinical neurophenomenology of pain. If that interests you, by all means get involved.

A complex mapping of the interior sense: why Damasio’s theory of embodied cognition focuses on the brainstem and viscera

If, like me,  you are interested in the biological dimensions of cognition, consciousness, and phenomenology, you tend to study the cortex.  Attention, decision-making, having a sense of self, perception, visual awareness, and many other key higher mental processes are modeled with data from cortical measurements, and especially with recent neurodynamics and computational neuroscience, there are increasingly sophisticated theories about the underlying mechanisms. But the cortex possibly gets too much attention compared to the rest of the brain and body.  This is partially because it indeed makes us human, but also for practical reasons, much of what we know about the brain comes from EEG research that with people is usually limited to scalp-based cortical signal acquisition. Dig a little deeper, say, when learning about emotions, and the student or scholar gets at least cursory introduction into the sub-cortical, emotion-regulating structures of the limbic system such as the hippocampus, thalamus, and hypothalamus. Our sense of salience, that things matter, our bodily sensations, our emotions and drives are associated especially with these sub-cortical structures. The study of how the brain processes emotions and bodily sensations has pointed some psychologists, neuroscientists, physicians, and philosophers in recent decades towards the idea of the experienced, phenomenologically lived body as the basis of consciousness and the self (or “self”). The growing sense for some of us about the limitations of traditional computationalist/cognitive theories has led to to the idea that mind and brain must be understood as “enactive“: via  evolutionarily and environmentally situated, physiological, embodied processes that “bring forth an experienced world”. Whatever cognition is, more than a few of us cognitive scientists nowadays think of it as somehow based in temporally ongoing, fleshy, existentially meaningful conscious life, or phenomenology. The mechanics of embodied mind, and the embodied basis of phenomenology, are very poorly understood by cognitive neuroscience, psychology, and medicine. Only very recently has there been a revival of interest especially in how visceral body states get processed by the peripheral nervous system and subsequently transformed by the central nervous system. One could understand this as a subfield of neurophenomenology:  how the brain and body enable “the bodily feelings I have now”, the experiential phenomenology of the internal body (if you have poked around this site you may have seen my own 2011 dissertation work was on this very subject). The rise of interest in embodied cognition has been hugely advanced through the work of the neurologist Antonio Damasio. This pioneer of embodied cognitive neuroscience has been focusing the attention of the psychology and cognitive neuroscience communities on the brainstem as the basis of consciousness.  The brainstem is not the usual topic when scientists bravely try to model conscious aspects of cognition, and my sense is that in the public mind it tends to register mostly when someone famous has medical problems as a result of brainstem damage causing loss of core visceral regulatory processes, such as with the death of Michael Jackson. In Damasios’ account, it is not merely a bit player in the grand drama of how body produces consciousness, but plays a starring role. Damasio (2010) states in Self Comes to Mind:Constructing the Conscious Brain , “I believe that the mind is not made by the cerebral cortex alone. Its first manifestations arise in the brain stem . ” (p. 75).

Courtesy Wikimedia Commons

Above is the brainstem, in red.  It receives inputs from the spinal cord, called “afferents”, that deliver signals from sensory nerves distributed throughout the body. These sensory nerves are affected by the homeostatic and visceral states of organs, such as our heart beating, the fullness of our bladder, blood sugar levels, the gas exchange in our lungs, and so forth. How much of the time these nerve signals resulting from visceral processes enter into conscious is a murky business. Cognitive scientists and others researching consciousness have not particularly referenced interior body psychophysiology and internal body-sensation in most theories about consciousness, but the work of Damasio is changing that. In general, research on the perception of visceral states or “inner psychophysics” goes in and out of scientific fashion, according to Gyorgy Adam’s wonderful overview of many decades of research, Visceral Perception: Understanding Internal Cognition.

Courtesy Wikimedia Commons

Below is an MRI of a beating heart and other visceral organs, with the spine visible. Afferent nerves “encode” information (or “information”) about the homeostatic and other dynamics of these systems, and send signals to the spinal cord and brain.

Courtesy Wikimedia Commons

While the idea that the brainstem produces the first manifestations of consciousness may seem radical, Damasio cites experimental evidence that perception of visceral states is mediated by the brainstem’s nucleus of the solitary tract and the pons. This gives us a window into understanding interoception:  the awareness of our visceral organs and internal body (though I think interoception also refers to unconscious signals from bodily organs affecting the brain and possibly influencing unconscious cognition). Building on generations of basic research on the neurophysiology of visceral perception, Damasio (2010) defines interoception as a “complex mapping of the interior sense” (p. 97). He emphasizes this occurs through an interoceptive network involving significant processing by the brainstem, which, unlike a mere relay, receives, processes and integrates afferents from the state of the visceral organs, and in turn projects to the thalamus. Through the work of Damasio, Bud Craig and others, we can model cognition as based in a central nervous system which filters and transforms signals from the lifegiving organs of the body. Building on their contributions, here is how I understand the neurophenomenology of visceral perception to work: our body organs are responding to existential life needs, our brainstem gets signals from the body organs and actively filters and transforms the signals, and in turn projects to the thalamus. Thalamo-cortical fibers then make synapses with neurons in the insula, cingulum, and somatosensory and orbitofrontal cortices, regions implicated in interoceptive activity and cognitive processes handling internal body information.  These areas all contribute to both consciousness in the foundational sense Damasio is investigating, and also produces specific awareness of our emotions and of our interior bodily sensations, such as feeling hungry. What goes on at the final stage, when cortical regions take the transformed bodily signal from the brainstem and thalamo-cortical processing, and somehow produce changes in consciousness? That gets into very complicated territory, and nowadays some of our most progressive thinkers use ideas and mechanisms from physics, such as Walter Freeman’s work on cortical neurodynamics, or that of Varela and colleagues. As of 2013 the dynamical aspects of interoception do not seem to be on many people’s radar besides mine and maybe a few others. What does it all mean for theories about the mind? If we accept that thalamic relay nuclei, activated by processed bodily interoceptive inputs in the brainstem, engage in further processing, and subsequently synapse on to (probably) dynamically interactive interoceptive centers in the insula and orbitofrontal, sensory, and cingulated cortical regions, what do we then understand about consciousness and cognition? As far as I can tell, the heart of Damasio’s theory is that visceral and homeostatic body states are “mapped” on to the brain via the brainstem,  and this mapping is what consciousness and the sense of self is “made of”. As we are organisms needing to engage in the right sort of behavior to survive, we depend on our sensory and visceral organs functioning appropriately. Our minds are thus built out of an evolutionarily developed machinery of life preservation. Put another way: the interior chemical milieu in our viscera affects nerve signals into the brainstem, and brainstem-mediated afferent signals tell our brain and mind about the state of our organs by projecting to the “gateway of the cortex”: the thalamus. A series of cortical regions process the thalamus gated body-signals, some of which are  cognitively and phenomenologically processed by a person as more emotionally and behaviorally salient, such as signals associated with food and thirst, pain and sex, and fighting or fleeing. Damasio, never one to shy away from big ideas and bold claims, sums up the state of his thinking in a 2010 interview:

Feelings, especially the kind that I call primordial feelings, portray the state of the body in our own brain. They serve notice that there is life inside the organism and they inform the brain (and its mind, of course), of whether such life is in balance or not. That feeling is the foundation of the edifice we call conscious mind. When the machinery that builds that foundation is disrupted by disease, the whole edifice collapses. Imagine pulling out the ground floor of a high-rise building and you get the picture. That is, by the way, precisely what happens in certain cases of coma or vegetative state. Now, where in the brain is that “feel-making” machinery? It is located in the brain stem and it enjoys a privileged situation. It is part of the brain, of course, but it is so closely interconnected with the body that it is best seen as fused with the body. I suspect that one reason why our thoughts are felt comes from that obligatory fusion of body and brain at brain stem level.

Can we not agree, that this is a profound way of thinking about the human condition?   Buy me a beer!

experimental physiology, interoception, and body knowledge

The work of experimental physiology researchers, such as Gyorgy Adam (1998) and Oliver Cameron (2002), as well as the psychologist James Pennebaker (1982) have opened up our understanding of how our cognition, brain, and peripheral nervous system allow us to know about our internal states. Such research probes the ability of people to sense and perceive processes and events interoceptively or visceroceptively-sensation via the visceral organs, typically the gastrointestinal tract or cardiovascular system. In a series of experiments lasting decades, described in Visceral Perception: Understanding Internal Cognition, Adam and colleagues (1998) painstakingly measured the ability of human subjects to perceive visceral changes. While much of their work is of primary interest to physiologists, for the present purposes it suffices to emphasize these claims and implications:

• The classical conception of the viscera, emphasizing their autonomic (maintaining homeostasis) activity, has not generally taken into account that sensory nerves innervate these organs.

• There are “dim and murky” but experimentally verifiable unconscious and conscious perceptions of these organs’ states.

• Conscious perception of visceral or interoceptive changes will tend to be “contaminated” with skin/surface based “somatic” perception, making “pure” visceral perception very difficult to verify.

• While cognitive neuroscience has fixated on the central nervous system, humans unconsciously and experientially are affected by various peripheral nervous system activities in the insides of their bodies, appropriately titled internal cognition (Adam, 1998).

Adam stresses the provisional, rather than the definitive, state of scientific knowledge of such concepts. Cameron (2002), in Visceral Sensory Neuroscience: Interoception, builds on Adam’s and other research, and attempts to contextualize what is known about internal body perceptions, skin and touch sensations, muscular control of movement, and other sensations. He addresses fundamental questions about how to taxonomize body knowledge, and writes that (pp. 274-275):
Rather than considering interoceptive processes, perhaps defining an overall bodily sense (or more than one-bodily senses) might be more appropriate…Would it not be more appropriate to define (as has been done by others) a bodily sense, including interoception, proprioception, labyrinthine function (i.e., the experience of the body in space), and other afferent information from the body?

The tentative appraisal of Adam and Cameron can only convey a sense of the complex nature of the phenomena at hand. Body knowledge, symptom perception, interoception, visceroception, and internal cognition are overlapping terms which need to be disambiguated. Yet this task is made all the more difficult because of the complexity of the problem of assessing how accurate people are at knowing their internal states.

Models of body knowledge are informed by practical medical and clinical needs. Physicians and clinicians routinely ask patients to report on their bodily sensations, while cognitive scientists, neuroscientists, and experimental psychologists often request subjects to verbally report on their perceptions. How true or “veridical” verbal reports are about objectively-measurable phenomena such as heart rate or blood pressure is a subject of debate. An extensive review by Pennebaker (1982) in The Psychology of Physical Symptoms of numerous results of studies measuring the abilities of normal humans to accurately report on physiological state found some limited evidence for accurate monitoring and reporting, but the bulk of data suggested people are poor at such tasks.

While this view may indeed represent something of a consensus, other authors (Fisher, 1966); (Adam, 1998) emphasize instances of relatively accurate capacity for interoception or perception of internal organ state, accuracy of perception of changes in external stimuli such as light or sound intensity (Stevens, 1975), practical necessity in clinical and medical contexts of asking patients to introspect and report on body state (Heilman and Valenstein, 2006) or numerous other perspectives that variously substantiate the accuracy and/or utility of verbal reports of sensation and perception. New data should be generated to shed light on two important (and overlapping) issues:
-the relative accuracy of verbal reports, which can be provisionally understood as representative fidelity to access to physiological state information.

-the neurobiological mechanism(s) by which people monitor and “get information” about their internal states.

The first issue above typically requires comparison of subject evaluations compared to objective measurements, while the latter usually involves imaging technology, such as EEG, fMRI, and other technologies. A model adequate to explain the results of both data sets will require bridging concepts that serve to link cognitive and biological levels of description. It should not be assumed at the outset whether or not information-processing models are up to that task. It may be that concepts from outside information-processing theory will be required to explain the data.

How accurate are people at knowing what is happening inside their bodies?

Were people utterly inaccurate at judging their body state and reporting on it, clinical medicine would be deprived of a critical tool.  Evidence has accumulated that in certain circumstances, some people are evidently able to access information about the physiological processes inside of their bodies, and to report on it.  Experiments seem to demonstrate that some people are relatively accurate perceivers of symptoms or physiological state (Jones and Hollandsworth, 1981), (Adam, 1998), and that subjects can be ranked into good or poor estimators of internal state; for instance, with perceivers of heart rate (Schandry, 1981).

When we are actually aware of specific processes inside our bodies and can state this verbally, it would seem that in some fashion unconscious information (or unconscious “information”) has generated or has been transformed into knowledge. However, there is contradictory evidence about accuracy of symptom perception: how good people really are at perceiving various physiological states, and how accurate symptom-reports or other verbal-reports actually are. Many studies have yielded data consistent with the idea that people are not particularly good at accurately reporting on their symptoms or physiological states (Pennebaker, 1982). It is worth pointing out the assertion that people are generally inaccurate about knowing about physiological processes in their bodies reformulates the principle that humans lack epistemological privilege concerning introspective or verbally reported data. In considering the question: are we are likely to be in error when we report on the contents of what is in our minds, or not, it is critical to appreciate the persuasive interpretation of experiments written up in papers such as “Telling More than We Can Know” by the psychologists Robert Nisbett and Timothy Wilson (1977), which seems to show how introspection-based retroactive judgments can are in error.  This category of research typically features subjects placed in circumstances where their choices are influenced by variables controlled by experimenters, and who give explanations for their choosing that display incorrect “folk psychological” constructions. Nisbett and Wilson’s analysis can properly interpreted as to cast doubt on the ability of people to know the causes of our behavior and “higher order” information-processing, and can be summed up with their statement that people may possess “little ability to report accurately on their cognitive processes” (p. 246).

However, I assert that this valuable critique of retrospective judgments has been improperly extrapolated to support a broad skepticism about introspection, what I shall call the “received view” or the “overly skeptical view”, which I might sum-up as the belief that introspective data should generally be regarded with skepticism. As has been noted by careful researchers on introspection, (Schwitzgebel, 2006), this more general rejection of introspection certainly goes beyond what Nisbett and Wilson argued: while they do indeed assert that the evidence of numerous studies shows people are poor at using verbal report-based introspection to the cognitive process behind our judging and deciding, they do not support a general disdain for introspective data. Rather, they state that instead of arguing that introspective reports should simply be discredited, while people do not have introspective access to the cognitive processes, they do have such access to the contents of their cognitions. For instance, Nisbett and Wilson (pg. 255) state that introspection can yield forms of knowledge: knowledge about cognitive content, as an everyday person:

“…knows what his current sensations are and what almost all psychologists and philosophers would assert to be “knowledge” at least quantitatively superior to that of observers concerning his emotions, evaluations, and plans”

Furthermore, the “received view” that introspective reports are to be generally regarded with suspicion is in tension with the clinical use of patient introspection, as well as the high accuracy ratings sometimes displayed in experiments where subjects are asked to evaluate their own physiology. Therefore, while showing appropriate regard for data suggesting limits on introspective access to cognitive information (indeed I will suggest that models of body-knowledge should account for this data), I will nonetheless highlight certain clinical and experimental data that support the following assertion, which  contradicts the view that introspective data should be generally regarded with skepticism:

There exist cognitive processes that allow people to access internal body-state or physiological information in a way that enables fairly, or even highly, accurate verbal reports.  Insofar as this is true, people evidently have some degree of epistemologically privileged access to internal body state or interoceptive information. This relative privilege allows for knowledge of the body, as distinct from mere beliefs.

However, if this is true, some accounting of to what degree or how true it is, with which mitigating conditions, and with what reference to underlying cognitive and neurophysiological mechanisms would be necessary.  For that matter, even if true, demarcating the explanatory power of this principle relative to data adequately explained by the “received view” or “overly skeptical view” is of critical importance. It may be that only special or rare abilities are at issue here, and that the people who have privileged access to their internal physiological information are outliers.

Body-knowledge: what is it?

I use the term“body-knowledge”  in my dissertation research primarily to refer to the experience of knowing about one’s own body, and especially embracing perception and assessments of the body through the body.  It is meant to straddle the classic cognitive psychology distinction between explicit knowledge that is verbalizable, and implicit knowledge that may only be revealed through experiments. Trying to define the term brings up a number of questions:

-How is “neurophysiological information-processing” related to “body- knowledge”?

-To what extent does the distinction between conscious and unconscious knowledge need to be invoked to explain that relationship?

-Should beliefs about the body be understood as part of body knowledge? What about attitudes, expectations, and desires concerning one’s body?

-Do the properties of the body vis-à-vis external objects and the external environment factor in, such as my knowledge of my ability to lift x kilograms of weights, or to effect changes in the world with my body?

-How is body-knowledge related to body-state information access?

This latter phrase can be thought of as “internal perception of information about the body”. For present purposes a heuristic understanding probably should suffice: body-state information access refers to what content an individual can perceive, sense, or detect about their body, but also to putative notions of information-processing in the afferent or other nerves that produce the content. As the term “cognition” signifies both mind as a collection of unconscious systems and (however problematically) mind as consciously experienced, body-state information access, as I use the phrase, straddles the divide between subjective and objective aspects of the body (compare to Merleau-Ponty’s (1968) notion of the “corporeal” or “the flesh”). One might extend the concept to mean that body-state information access also refers to a sort of “information gain” in bodily perception: for instance, being aware of digestive processes where one was not previously.

Interoception is another term needing examination: while classically interoception refers to perception of the visceral organs in the inside of the body, consider Bud Craig’s (2002) proposed redefinition (pg.655):

“Interoception should be redefined as the sense of the physiological condition of the whole body (including pain and temperature), and not just of the viscera”

Even if this broader sense becomes accepted, interoception will still include the sense of “interior perception”.  The more expansive signification should then overlap with somatic cognition, a term deployed by neuroscientists (Tanosaki, Suzuki, and Kimura, 2002) who use it to signify perception using body parts such as fingers, and also internal cognition, or even visceral cognition, labels used by researchers who model the relationship of the internal organs to the nervous system and perception (Adam, 1998, pg 156-159).

Compare these to body cognition, which might not only embrace the idea of knowledge of one’s lived, experienced body, “thinking with the body,” but also the somatic, visceral,  neurophysiological, and cognitive systems making the perception and knowledge possible. “Body cognition” would seem to have experiential or phenomenological (that is, felt) dimensions, but should also refer to what are commonly understood to be unconscious mental, neural, and other physiological processes enabling this knowing. The profusion of terms may reflect the inherent complexity of the systems involved, our partial and provisional understanding, or both. Analyzing how the notion of information relates to models that explain how unconscious neurophysiological processes give rise to conscious ones is a particular focus of my project.

As I will be use the term, body-knowledge embraces the notion of using the body as the means to perceive or assess itself, such as with symptom perception. The study of body cognition involves perspectives from many fields, but could be understood as a subset of embodied cognitive science, which differs from standard approaches to the extent that it emphasizes overcoming the Cartesian split between subject and object implicit in cognitive science, and the coupling of human mental activity to a meaningful world. One of the goals of a cognitive science of embodiment would be to construct a model of body knowledge good enough to explain how the embodied brain and mind make knowledge of the body, sensing or perceiving using the body, and the ability of people to use directed attention and introspection to gain “true information” or validated knowledge (compare to beliefs) about the body.

As I use the terms, body-knowledge and body-state information access refer to both experiential-phenomenological knowledge (“I feel hungry” or “I have an itch on my scalp, but not as bad as earlier”) that may form the basis of verbal reports as well as the unconscious, and presumably not explicitly stateable, underlying information processes comprising cognition. This distinction between stable and explicit and non-stateable or implicit knowledge is not a trivial one. Cognitive science, neuroscience, and psychophysiology propose that our conscious awareness and experience of information about the body to be to be somehow made of or caused by unconscious information, because cognitive processes are understood to be mostly unconscious.  Varela, Thompson, and Rosch (1991, pg. 49) point out that cognitive science:

“…postulates processes that are mental but that cannot be brought into consciousness at all. Thus we are not simply unaware of the rules that govern the generation of mental images or of the rules that govern visual processing; we could not be aware of these rules. Indeed, it is typically noted that if such cognitive processes could be made conscious, then they could not be fast and automatic and so could not function properly”

The brain and the internal state of the body

Hugo Critchley et al. (2004) state that (pg.189) “the internal state of the body is conveyed through a dedicated lamina-1 spinothalamocortical pathway that converges with vagal afferents”. These afferent nerves are noteworthy for the smallness of their diameter in comparison with the larger afferents that apparently deal with proprioception, the perception of the body in space. Physiologist Bud Craig has written that the difference in size of these nerves signify “a simple physiological distinction between the inside and the outside of the body.’’ (Craig, 2002, p. 657)

The heart connects to the brain through the autonomic or visceral nervous system, traditionally thought to operate mostly without conscious control (breathing being a notable exception).  The sympathetic projections of the autonomic system can increase heart rate in stressful situations, while the parasympathetic fibers slow the heart down when appropriate. There are also two sets of nerves connecting heart and brain:  spinal nerves,with the dorsal root containing afferent sensory projections, and the ventral root for efferent motor fibers. In addition to spinal nerves, the vagus nerve supplies parasympathetic fibers including mostly (85%) afferent fibers, while the rest are brain-to-viscera efferent (brain to motor) fibers that project from the medulla oblongata in the brainstem, and which, if working properly, can rapidly increase or decrease heart rate as needed via innervation of the cardiac muscle. The afferent fibers projecting from viscera to brainstem do so viscerotopically, preserving information about spatial extension or location of the viscera in the body that is subsequently processed (many researchers would say “represented”) in the brain.

Evolutionarily/phylogenetically ancient structures such as the nucleus of the solitary tract and the pons transform the incoming afferent “signal” from viscera such as the heart, and eventually pass it along to the “gateway to the cortex” or thalamus. From there thalamo-cortical fibers project to regions such as insula, cingulate gyrus, and somatosensory and orbitofrontal cortices, regions implicated in interoceptive activity and cognitive processes handling internal body information.   These regions have been investigated for processes corresponding to cardiac activity:

Insula, or the Island of Reil

somatosensory cortex with S1 and S2 colored

fMRI of orbitofrontal cortex

Some researchers (notably (Olga Pollatos and Rainer Schandry, 2004), (Gray et al., 2007) have identified a heartbeat evoked potential that can be detected with EEG measurements: an increase in amplitude of neuroactivity or neuronal firing, detectable after averaging many instances together and subtracting “background” activity as noise,  that seems to occur after a heartbeat. It is intriguing, and possibly of great significance for models of body-knowledge and interoceptive information access, that higher amplitude in the heartbeat evoked potential correlates well with better heartbeat perception in the Pollatos and Schandry research.

Data coming from fMRI and other imaging studies (magnetic electroencephalography, or MEG, and cerebral blood flow, or CBF) should shed additional light on the relative activity levels of cortical and subcortical structures that enable conscious perception of heartbeats, as well as unconscious central nervous system response to cardiac processes.

symptom verbal reports and existential-physiological discrepancy

While the anatomical basis of how nerve projections enable perception of the body is rather well known, physicians confront situations where patient verbal reporting about symptoms does not match models based on neurophysiological mechanisms. For instance, the Merck Manual Medical Library (2009) states:

“Painful stimuli from thoracic organs can produce discomfort      described as pressure, gas, burning, aching, and sometimes sharp pain. Because the sensation is visceral in origin, many patients deny they are having pain and insist it is merely discomfort”

The Mayo Clinic Heart Book (Gersh, 2000) describes the concept of uncomfortable feeling of thumping inside the chest known as palpitations, but does so from the point of view of patients (pg. 38):

“Although the apparent cause of the thumping in the chest would seem to be the heartbeat, this is not always the case. Some people have a normal heart rate during their palpitations. Presumably, they are either anxious or experiencing chest wall twitching that is mistaken for heartbeats”

Situations where the “folk physiological” (see Churchland, 1989, for a description of expert knowledge vs. folk beliefs) understanding of the body is apparently falsified by science can be labeled examples of existential-physiological discrepancy (Laughlin, McManus, D’Aquili, 1990). Mismatches between body-as-experienced compared to the “objective body” of scientific medicine and physiology (including the feeling of “phantom limbs” by amputees) are based on the idea that people may often have very limited “true” access to physiological processes. A more commonly presented variant or subset of this principle is the idea of “referred pain”, where the region causing understood to be causing the pain is spatially removed from the area where the patient senses it.

The Merck Manual (2009) gives an example: sometimes pain felt in one area of the body does not accurately represent where the problem is, because the pain is referred there from another area. Pain can be referred because signals from several areas of the body often travel through the same nerve pathways in the spinal cord and brain. For example, pain from a heart attack may be felt in the neck, jaws, arms, or abdomen. Pain from a gallbladder attack may be felt in the back of the shoulder.