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The pain system is so complicated!

Posted Dec 12 2010 2:17pm

There are a couple of ways to approach the problem of pain – the one I grew up with is the medical one: diagnose the problem, fix the problem, life returns to normal.  The person’s role in this is to be open about what is wrong, let the treatment provider know the information (and only the information) relevant to the problem, follow the medical instructions, and all will be well.

Of course the majority of readers of this blog can see some short-comings in this model.  It forgets that people choose when to seek treatment and that they make decisions about this based on ‘common knowledge’ (or what the community around them says they should do), family history, current stressors and activities, degree of distress, and how much the symptoms get in the way of living life (or represent a potential something that might get in the way of life).

Not only this – people process what happens to them.  They relate what is happening now against what has happened in the past, and how much this experience has affected them.  They have thoughts, emotions, they take actions on the basis of these thoughts and emotions.  And some of these thoughts are not exactly accurate – but none-the-less they affect the person living his or her life.

For some people who use a medical model (and even some who say they use another model), the whole area of thoughts, emotions, attention, perception – it’s just so complicated.  And so their focus is entirely on the bits of the nervous system they can understand.  Bits below that amorphous ‘brain’.  So if we take a look at many diagrams and descriptions of the nervous system, we start at the outside, and work our way in towards the central nervous system, maybe show some connections at the spinal level, perhaps go even as far as the thalamus – but the rest is some sort of blank.  Take a look at this excerpt, written for postgraduate students, written by a medical practitioner lecturing on the neurobiology of pain:

As the second order neurons are activated, transmission continues from the dorsal horn to higher centres. The axons of second order neurons cross the midline in the anterior white commissure and ascend in the anterolateral funiculus (spinothalamic tracts) via the medulla and the midbrain to the thalamus. Transmission from the thalamus to the cerebral cortex occurs via third order neurons.
Perception is the final phase of nociception and it occurs in the cerebral cortex. It involves interpretation and evaluation of the transmitted neural signal to form the subjective experience of pain

Thus nociception pathways extend from the periphery, where transduction occurs, and transmit nociceptive stimuli through the peripheral nervous system and the central nervous system to the cerebral cortex, where perception occurs.

While this isn’t incorrect, it falls far short of our knowledge about how our brain detects and brings to consciousness threats to our body.

If you’re looking to do better than this. If you’re serious about learning about how our nervous system works to protect us – and learn about potential areas of the nervous system that could be dysfunctional and contribute to things like chronic pain – then three papers I’ve recently been reading are well worth a look.

They’re all from the journal Brain Research Reviews, and were published in 2009 – but don’t let that stop you from reading them!

The first is Descending control of nociception: Specificity, recruitment and plasticity by M.M. Heinricher, I. Tavares, J.L. Leith, B.M. Lumb, Brain Research Reviews, 60, 214-225. doi:10.1016/j.brainresrev.2008.12.009
The next, Forebrain pain mechanisms by Vasco Galhardo, Sabatino Maione, Sean C. Mackey. Brain Research Reviews, 60, 226-242.doi:10.1016/j.brainresrev.2008.12.014
And the final one, The cerebellum and pain: Passive integrator or active participator? by Volker Neugebauer, Eric A. Moulton, Jeremy D. Schmahmann, Lino Becerra, David Borsook. Brain Research Reviews, 60, 14-27. doi:10.1016/j.brainresrev.2010.05.005

Before readers start yelling things like ‘You geeky grrl, you she-nerd’ – I didn’t enjoy neuroanatomy all those years ago when I first started working in pain management.  Now, however, I watch the information unfolding about the role of these areas of the brain and nervous system, and I see how important they are in our understanding of our experience of pain.  It is not enough to look at the lower levels and the periphery to ‘know about’ pain.  While it’s true to a certain extent that (quoting from my learned medical friend again):

…the experience of pain is fundamentally related to tissue damage; it is the means by which an individual becomes aware that injury has occurred, is continuing to occur or is likely to occur. Thus the biological processes that enable perception of pain are vital to the body’s defence against tissue damage; they are normal, physiological processes essential for survival. They are the fundamental key to understanding pain for without them there would be no pain.

Where I disagree with him is that I assign a rather more significant role to the central processes that occur.

As I mentioned, most descriptions of pain systems begin at the periphery and work in – why not turn that upside down? Let’s start with the role that various parts of the brain play in first seeking information relevant to the primary goal of the person.  Is it to stay alive by swimming very fast to shore after being bitten by a shark? Is it to detect further harm after being sunburned? Is it to notice a discrepancy in inward-flowing information that doesn’t match what the brain’s neuromatrix expects?

For each of these situation, the brain is working hard to actively seek information from the tissues – so maybe we should start with the status of the brain and look at why it might selectively attend to and modulate ‘issues in the tissues’.  And maybe we might then start to consider that events occur to a person-in-context, not a tissue in isolation.

And yes, I know I haven’t even started to consider the family, community, social aspects of pain yet!

Neugebauer, V., Galhardo, V., Maione, S., & Mackey, S. (2009). Forebrain pain mechanisms Brain Research Reviews, 60 (1), 226-242 DOI: 10.1016/j.brainresrev.2008.12.014

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