Tuesday, May 14, 2013

Melzack's and Katz' new paper; Pain. Part 1. (First two sentences of the abstract)

Yes, it's called, simply, Pain. By Ronald Melzack, (see biography) and Joel Katz.

Wiley Interdisciplinary Reviews: Cognitive Science Volume 4Issue 1pages 1–15January/February 2013

I love this paper. I'm planning to deliciously and slowly devour every morsel of it, maybe taking several blogposts to do so, and report every flavour I find. Because I want to sink myself deep into this recent writing, lose myself, wander around inside his mind.


Here is the abstract:

"Pain has many valuable functions. It often signals injury or disease, generates a wide range of adaptive behaviors, and promotes healing through rest. Despite these beneficial aspects of pain, there are negative features that challenge our understanding of the puzzle of pain, including persistent phantom limb pain after amputation or total spinal cord transection. Pain is a personal, subjective experience influenced by cultural learning, the meaning of the situation, attention, and other psychological variables. Pain processes do not begin with the stimulation of receptors. Rather, injury or disease produces neural signals that enter an active nervous system that (in the adult organism) is the substrate of past experience, culture, and a host of other environmental and personal factors. These brain processes actively participate in the selection, abstraction, and synthesis of information from the total sensory input. Pain is not simply the end product of a linear sensory transmission system; it is a dynamic process that involves continuous interactions among complex ascending and descending systems. The neuromatrix theory guides us away from the Cartesian concept of pain as a sensation produced by injury, inflammation, or other tissue pathology and toward the concept of pain as a multidimensional experience produced by multiple influences. These influences range from the existing synaptic architecture of the neuromatrix—which is determined by genetic and sensory factors—to influences from within the body and from other areas in the brain. Genetic influences on synaptic architecture may determine—or predispose toward—the development of chronic pain syndromes."

OK, so even this much, the abstract only, contains depths I have yet to plumb. 

"Pain has many valuable functions. It often signals injury or disease, generates a wide range of adaptive behaviors, and promotes healing through rest."
1. "Chest pain may be a symptom of heart disease."
 It might make us go to the doctor. I should hope so. Any unusual pain anywhere in the trunk, especially in the front of the trunk, anywhere from top to bottom, would certainly drive me to pick up the phone to the doctor's office, or call an ambulance. Absolutely. Pain compels. 

2. "Memories of past pain and suffering also serve as signals for us to avoid potentially dangerous situations." I should think so! If you remembered falling down the front steps carrying a bag of groceries 20 years ago, breaking your ankle, chances are pretty high your brain would remember "steps=danger" every time you went to tackle some, especially carrying groceries, or anything. You might not be the first to volunteer to help a friend move. 

3. Pain makes us rest. Yes. If you don't move around for awhile freely, because the spinal cord/brainstem/critter brain takes over and stops motor output from happening fluidly, makes us have to figure out ways of guarding our bodies by giving us pain, the tissues will heal better, or so we think, except for when the time frame stretches out way beyond the length of time it usually takes for tissue to glue itself back together. Three months, and that's being generous. Even bone can knit (not be strong, but at least knit) by about 6-8 weeks

"Despite these beneficial aspects of pain, there are negative features that challenge our understanding of the puzzle of pain, including persistent phantom limb pain after amputation or total spinal cord transection."
1. Phantom limb pain, not the physical impairment, stops people from leading a normal life.
"Likewise, most backaches, headaches, muscle pains, nerve pains, pelvic pains, and facial pains serve no discernible purpose, are resistant to treatment, and are a catastrophe for the people who are afflicted." (page1)  On some level, yes they are. Yes pain is.
2. "Pain might be a warning signal that saves the lives of some people, but it destroys the lives of countless others." I guess that's assuming we want to be here in the first place, we feel embedded, and that life isn't just a piece of corn

3. Chronic pains are not preventive warning - they are the result of neural mechanisms gone awry.
Here are the first three references to support this statement:
1. Niv D, Devor M. Chronic pain as a disease in its own right. Pain Pract 2004, 4:179–181. (no abstract available) 
2. Siddall PJ, Cousins MJ. Persistent pain as a disease entity: implications for clinical management. Anest Anal 2004, 99:510–520. (full text) 
3. Woolf CJ. Pain: moving from symptom control toward mechanism-specific pharmacologic management. Ann Intern Med 2004, 140:441–451. (abstract only)

Skip to page 3:
 "In 1978, Melzack and Loeser described severe pains in the phantom body of paraplegic patients with verified total sections of the spinal cord, and proposed a central ‘pattern generating mechanism’ above the level of the section. This concept represented a revolutionary advance: it did not merely extend the gate; it said that pain could be generated by brain mechanisms in paraplegic patients in the absence of a spinal gate because the brain is completely disconnected from the cord. Psychophysical specificity, in such a concept, makes no sense; instead we must explore how patterns of nerve impulses generated in the brain can give rise to somesthetic experience."
Here is the reference: 17. Melzack R, Loeser JD. Phantom body pain in paraplegics: evidence for a central ‘‘pattern generating mechanism’’ for pain. Pain 1978, 4:195 – 210. (abstract only)
"Examines the proposition that chronic pain may be caused by a loss of sensory input. Cases in the earlier literature are reviewed, and new cases are presented of chronic pain patients who sustained total spinal cord sections. The completeness of the lesion was verified visually during surgical removal of injured tissue or as a result of segmental cordectomy to prevent nerve impulses produced by injured tissues from reaching the brain. Nevertheless, pain returned immediately or as long as 11 yrs later. The pain was usually felt in definite parts of the phantom body and was often described as burning, crushing, or cramping. The sympathetic ganglia—the only other possible route for nerve impulses from the legs—were also blocked in several patients without effect on the pain. There is convincing physiological evidence to show that deafferentation produces abnormal physiological activity in spinal and brain cells deprived of input. The cells fire spontaneously in high frequency bursts and may be triggered by inputs from adjacent structures; the abnormal firing may persist for hours after a single, brief triggering stimulus, and abnormal activity has been observed to persist for months. A model is presented which proposes that synaptic areas along the transmission routes of the major sensory projection systems, from the dorsal horns to the somatosensory projection areas in the thalamus and cortex, may become pattern generating mechanisms. (45 ref) (PsycINFO Database Record (c) 2012 APA, all rights reserved)"
This is a delicious, although tiny, little crumb. Cited by 318 since 1978 -  I can't access the paper itself. Seems like few pain investigators are interested in delving into pain that doesn't have a spinal cord with intact pathways attached. Yet, here we are. Edge of a cliff. Dang. 

Melzack stands by this paper. 

A bit further on, page 4, this: 
"the data on painful phantoms below the level of total spinal cord section, indicate that we need to go above the spinal cord and into the brain."
18. Melzack R. Phantom limbs and the concept of neuromatrix. Trend Neurosci 1990, 13:88 – 92. (abstract only, 513 citations)"The phenomenon of a phantom limb is a common experience after a limb has been amputated or its sensory roots have been destroyed. A complete break of the spinal cord also often leads to a phantom body below the level of the break. Furthermore, a phantom of the breast, the penis, or of other innervated body parts is reported after surgical removal of the structure. A substantial number of children who are born without a limb feel a phantom of the missing part, suggesting that the neural network, or ‘neuromatrix’, that subserves body sensation has a genetically determined substrate that is modified by sensory experience." 
19. Melzack R. Phantom limbs, the self, and the brain (The D.O. Hebb memorial lecture). Canad Psychol 1989, 30:1 – 16. (abstract only, 182 citations)"An examination of phantom limb phenomena has led to 4 conclusions: The experience of a phantom limb has the quality of reality because it is produced by the same brain processes that underlie the experience of the body when it is intact; neural networks in the brain generate all the qualities of experience that are felt to originate in the body; the experience of the body has a unitary, integrated quality that includes the quality of the "self"; and the neural network that underlies the experience of the body-self is genetically determined but can be modified by sensory experience. A theory is developed to explain these conclusions. It is proposed that we are born with a widespread neural network (the "neuromatrix") for the body-self, which is subsequently modified by experience. The neuromatrix imparts a pattern on all inputs from the body, so that experiences of one's own body have a quality of self and are imbued with affective tone and cognitive meaning."


These are: (page 4)

1. Phantom limbs feel so... real!
"First, because the phantom limb feels so real, it is reasonable to conclude that the body we normally feel is subserved by the same neural processes in the brain as the phantom; these brain processes are normally activated and modulated by inputs from the body but they can act in the absence of any inputs."

Even people without amputations can feel phantom limbs. It's become a bit of a parlour trick, even. Rubber hand illusions, etc., are being thoroughly investigated.  Even illusions that simply distort the visual perception of an arthritic hand, moving, lengthening, can help reduce pain that feels as though it comes from the hand. Is the pain coming from the real hand? Or from the "virtual" hand stored in a person's sense of self, or neuromatrix? 

2. Sensations, including the sensation of "pain", all the "qualities of experience" we feel from being in a body, can all be "felt" without any inputs from the body. 
"Second, all the qualities of experience we normally feel from the body, including pain, are also felt in the absence of inputs from the body; from this we may conclude that the origins of the patterns of experience lie in neural networks in the brain; stimuli may trigger the patterns but do not produce them."

References for this derive from the phantom limb studies listed above, and this one: 
21. Melzack R. Pain and the neuromatrix in the brain. J Dental Ed 2001, 65:1378–1382. Full access. 
But, also see Slater et al,  Inducing Illusory Ownership of a Virtual Body, Front Neurosci. 2009 September; 3(2): 214–220. (full access.)  

3. Human "Self"'s feel isolated from the rest, from others. 
"Third, the body is perceived as a unity and is identified as the ‘self’, distinct from other people and the surrounding world." 
Each human feels him or her "self" to be a vulnerable target, sticking out into space, center of the universe or something. This isn't entirely narcissistic, it's likely neurological. It likely drives us to be more social. To compensate we try to "blend in", not be a purple cow, because there is a primate instinct in there, to be part of a troop and stay safe

4. The "Self" is still inside a physicality, however, one that emerged.
"Fourth, the brain processes that underlie the body-self are ‘built-in’ by genetic specification, although this built-in substrate must, of course, be modified by experience, including social learning and cultural influences." 
You can't really exist (continue to emerge) without a physical substrate. It just doesn't work. 


So, here we are - I've sat and worked on fathoming this for hours, deliciously, and I'm still only two sentences into the abstract. This is turning into a total fugue. And I enjoy fugue. 

I intend to digest every word of this paper, in this deliberately repetitive and building fashion. 


B said...

Fabulous review. Every bit helps.

Amee said...

This is cool!