The body in the brain

November 23, 2017

The body in the brain

The research outlined here considers identity as it relates to our health. In particular, the way our bodies feel to us—our bodily identity, as distinct from other expressions of our identity.

 

Personal identity – what it means for ‘me to be me’ – is a difficult concept. It is difficult to define. It is difficult to agree upon. In spite of such difficulty, identity is very much in vogue. Our present socio-political discourse is saturated with references to identity and its implications. Gender or political allegiance are key examples. Our concepts of identity are also importantly involved in our moral judgements, social relationships and our health. This paper considers identity as it relates to our health. In particular, the way our bodies feel to us – our bodily identity, as distinct from other expressions of our identity.

Where might we start looking?

This article presupposes that the mind is of the brain. The mind-to-brain thesis means that anything mental (psychological) has a biological basis within the brain. That is, mental (psychological) processes – thinking, feeling, seeing, smelling, hurting – are processes that occur within and through the biology of the brain. Bodily identity, the lived experience of one’s body, is a psychological experience that has, therefore, a biological basis within one’s brain.

Neuroscience is concerned with understanding the biology of the brain. In turn, neuroscience should help us to understand the biological basis for bodily identity. We have multiple options for studying the living human brain, of which two broad approaches are relevant here. Firstly, brain cell activity can be measured in various ways using scanning machines (broadly labelled: brain imaging, e.g. with MRI). Secondly, there are certain functional tasks that [probably] require distinct nervous system processes to accomplish. We can learn about the implicated nervous system processes on the basis of people’s performance of these functional tasks (broadly labelled: psychophysical testing e.g. mental imagining of a movement activates particular brain networks).

The nature of our identity is represented in our brain

The aspect of bodily identity that we are considering relates to the ‘body representation’. It is helpful to think of the body representation as a continuum 1,2, with several semi-distinct elements. At the conscious end, there is the body image – our conscious experience of our own body 2–4. This, specifically, is the perceptual body image, which is somewhat distinct from the conceptual body image (our representations of the names/purposes of body parts) and the cultural/emotional body image (what we/others think of ourselves). We will not consider these latter two aspects of bodily identity. Body image is frequently discussed in popular contexts and we would all have experienced positive or negative responses to our own body image.

Moving into the non-conscious spectrum, there are the body schema and the body model. The body model represents the size and shape of our bodies at a high level of detail 5. It is essentially a hard-wired map or blueprint of our body’s dimensions. The body schema is a more general representation that integrates sensory and movement-related information with the body model to guide posture, balance and our sense of touch; among other functions 6.

We use the word representation to denote the biological embodiment of things in the nervous system. A thought, a memory, an emotion, even pain, are all representations. At the basic level, underlying the representation, there are networks of communicating neurons and supporting cells (glia)[*]. These cells carry signals that when used within a system of rules and mechanisms (termed, the neural code), produce the function associated with the representation 7 – the thought, the memory, the pain. It is well acknowledged that we are still working to understand exactly how this occurs 8–11. At the least, many networks will contribute to a representation and thus, these representations are complex interactions of many brain cells. This is true of the representations that underlie bodily identity. What this means is that the lived experience of yourself, how your body feels to you, is the functional product of electrical activity in intricate networks of brain cells.

Study disease to understand health: study dysfunction to understand function

We have learnt a great deal about ‘normal’ nervous system function from studying nervous system dysfunction. A good example of this is the early development in understanding of the functional roles of different brain areas based on studying people who had injured isolated areas of the brain. Similarly, we can learn from a variety of conditions where the nervous system differs in people with the condition, compared to people without, even if there has not been any brain injury. We call these differences nervous system reorganisation.

Chronic pain is a condition that exhibits nervous system reorganisation. There are differences in the structure (‘materials’), functional organisation (‘wiring’) and biochemistry (‘environment’) of the brain in people with chronic pain. Chronic pain is pain that persists past the point that it should, which for most things, is 3 months from when they start hurting[†]. I study chronic low back pain (CLBP), the most common form of chronic pain. People with CLBP display marked nervous system reorganisation. Importantly for our consideration here, people with CLBP also report disruptions to their identity in various forms. By understanding the dysfunctional nervous system and disrupted identity of people with CLBP, we now have an opportunity by which we may understand more about the normal functions of the nervous system as it relates to identity.

The nature of identity for someone in pain

We know from interviews that people with back pain view their backs as vulnerable and easily damaged 12–15. They may feel separated or disconnected from their back and who they want to be 16–18, which reflects a negative body image and conflict between their ‘lived’ and idealised experience. Pictures that people draw of their backs are distorted and may be missing sections altogether – for example, the outline of the trunk may be absent 19,20. These observations match their answers to questionnaires about how their back feels to them – shrunk, swollen or lopsided and difficult to monitor or control when moving 21–24. These data tell us that the bodily identity – the lived experience of themselves – for people with CLBP is not as it once was.

The basis of the disrupted identity is a distorted body representation

If we draw on the knowledge from psychophysical testing, we may begin to understand why identity is disrupted. Recall that psychophysical tests are reflections of the performance of nervous system processes. Thus, performances on psychophysical tests [probably] reflect the functional integrity of representations. We know that people with back pain’s response to touch on their back is altered: their ability to distinguish two simultaneous touches from one is reduced 20,25 and they struggle to localise where they are being touched 26. They also struggle to recognise the movements of others 27,28 and are less proficient at mental (imagined) movements themselves 29,30. Together, these data tell us that the functions of the body representation are disrupted. This suggests that the reason for the disrupted bodily identity of people with CLBP is probably that there are disruptions in their body representation.

Exploring the basis for disrupted identity in chronic back pain

What we don’t yet conclusively know is why these representations are disrupted. This is where my work fits in. The relevance to our consideration of identity is that if we can identify the biological basis of the differences in these representations (between people with and without CLBP), then that may indicate why they are distorted and giving rise to a disrupted identity.

For disruptions to occur, there is probably some change in the brain cells that form these representations, there is probably nervous system reorganisation. This may be a change in structure (materials), functional organisation (wiring) or chemistry (environment). In my studies, I have looked at the structure and biochemistry. In particular, where in the brain the differences in structure are and which chemical levels are different. As mentioned, nervous system reorganisation is generally a feature of chronic pain. My research is a precursory step to understanding why there are differences – we must first understand if there are differences in people with CLBP.

My team and I combined all of the data from MRI studies of brain structure in people with CLBP. This gives us a much-improved ability to separate real differences from chance findings that may have occurred. We found that there were numerous reports across individual studies, yet when these were combined the results suggested there are no real brain differences at all (Bagg et al. unpublished data). We followed a similar process with all the studies of the brain’s biochemical environment. This was less informative because much less data could be combined. Nonetheless, the available data told a similar initial story – there are numerous, inconsistent, reports of differences in brain biochemistry in individual studies (Bagg et al. unpublished data). This means that we don’t currently know with certainty that there are differences in the brain that may underlie the representations for identity. We need to collect more, better quality data.

Implications for our understanding of bodily identity and concluding remarks

These findings do not present as a problem for our consideration of bodily identity. At this point it means that we can’t say if differences in brain structure or biochemistry underlie the distorted representations that subserve bodily identity in people with CLBP. Simply, we cannot make a conclusion on the nature of disruption to the biological basis for bodily identity, yet.

We have covered a considerable amount of ground in this article. We have considered that all psychological experiences, of which identity is one, have a biological basis in the brain. We call these representations and we know that they are the functional output of activity within networks of brain cells. We have considered that the body representation is one such representation that underlies our identity.  We have seen that the identity of people with chronic back pain is disrupted and that this is due to disruptions of the body representation. Finally, I have described my work where I have explored the reasons for this re-organisation.

            Studies are ongoing to refine our understanding of body representation and its constituents. At the least, it should be clear that the representation of your body in your brain is a key contributor to your bodily identity – your lived experience of your own body.

 

Matthew Bagg is currently undertaking doctoral research in chronic pain treatment at Neuroscience Research Australia and UNSW.

 

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[*] Together, neurons and the four types of glia constitute the cells of the brain. Glial cells are more numerous, less widely studied and less understood than neurons; though no less important, with important roles in immunity and communication between neurons, among others 31.

[†] Pain is a protective response. Usually, things start to hurt because of an injury – some sort of damage to the body. It is important to know that this is not always the case; there need not be any damage for you to start hurting. When there is injury, healing will be complete by 3 months. So there is no need for protection via pain any longer.

 



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