Referred Pain

[anoopbal]

From what I understand, reffered pain is due to the homunculus being confused. For example, low back nerves getting pinched but pain felt only running down in the legs and not in the area pinched. Since the nerve was suposed to be coming from the leg, the homunculus reffered the pain or reported the pain in the legs than that at the low back.Another example is bumping ypur elbow and feeling tingling in your fingers.

Is there any other explanation for reffered pain other than the homunculus?

Thanks
Anoop

[Bas]

My understandiong is a bit different, but maybe we have a bit of a language issue here as well.
I understand a signal to/in a cortical representation and its related pain experience can be generated anywhere in the related neurological pathways. I don't really think the homunculus is confused - it is working as accurately as ever with the imput it gets; the input is not always linear and can be from "anywhere" in the system.

My apologies to all for limiting mysefl to the simplest possible terminology - it is for my own benefit...I process info that way so when I learn, I can put it in patient-(and Bas-)friendly language...

[anoopbal]

I think I worded it wrong. Let me rephrase it. Why the nerve in the low back get pinched but th pain is felt in the legs and not at the area where it is pinched.

thanks
anoop

[Jon Newman]

Hi Anoop,

If we were wired like lights in a room, with a single pathway leading from the stimulus (flipping the switch) to a response (the light going on or off) then one should be shocked to see what you describe. The fact is that we are not wired that way.

The homunculus isn't like a little man in your head making decisions (hence cannot become confused) but is more like a map. Butler uses the term "smudging", something that can happen to a map (although refolding a map seems to be a much more common problem than smudging). I think what smudging is referring to is that more of the map is being stimuluted (for a given perihpheral input) or perhaps the map is fine but more of what it represents is making it to conscious perception.

To sum up; I don't really know.

[bernard]

Hi all,

A nerve is a communication vessel: a kind of very large pathway (in # of wired lines).

If you apply a damage on the foot "wires" anywhere on the "cable" then you feel a problem at the brain foot area.

It does not matter where the injury occurs, only the injured "wires" are important. BTW, the nerve itself is sensitive and adds a "personal" component that helps us to make a differential diagnosis.

[anoopbal]

It does not matter where the injury occurs, only the injured "wires" are important. BTW, the nerve itself is sensitive and adds a "personal" component that helps us to make a differential diagnosis.

So this sort of phenomenon occurs because thats how it is interpretted by the homunculus. So the organization of the humunculus ( and the nerves) leading to it) is main reason why this phenomenon occurs, right?

thanks
anoop

[emad]

Hello Anoop:

I think ,in case of complete nerve cut there will be no numbness or tingling referring distal (by the way the referring could proximal as well) .
As for partial inturrption /comperssion /load there will be refrred numbness ,may be referred pain ( i do nOT why referring coud be pain ,numbness ,tension ,,,,,,,,,,) because the Nervous System is one entity /circuit including both peripheral and central , i do not like any more classifying Nervous System asw peripheral and central . So in case of comperssion it referrs may be because of conductivity ...!!!!!

Cheers
Emad

[Diane]

From what I understand, reffered pain is due to the homunculus being confused. For example, low back nerves getting pinched but pain felt only running down in the legs and not in the area pinched. Since the nerve was suposed to be coming from the leg, the homunculus reffered the pain or reported the pain in the legs than that at the low back.Another example is bumping ypur elbow and feeling tingling in your fingers.

Is there any other explanation for reffered pain other than the homunculus?

Homuncular involvement in pain and referred pain are two quite different things which may overlap but don't always. You could use the metaphor of pain as a fire and various contributing factors as fuel load, as Barrett has done in many of his essays.
For instance, a "smudged" homunculus adds a load to the fire in the case of an amputee with phantom limb pain. The homunculus must be "treated" indirectly, through another sense like vision, because there is no periphery to treat kinesthetically. (See mirror boxes.)

Pain felt in the "body" can also be from a trapped "twig"on the neural tree somewhere out in the periphery. But there is absolutely no gauge by which one can measure size of twig or location of entrapment or its severity or even where along the nerve entrapment has occurred, against the size of the suffering of the pain. There's no way to gauge the brain's response to hypoxia in the periphery by outputting pain, in other words.

Also, in a given nerve anywhere, a situation wherein hypoxia is happening in one part of the nerve can be felt anywhere along that nerve, from proximal to distal, as Bernard mentioned.

[Jon Newman]

Hi Anoop,

I've already offered that I don't actually know the answer but I know a little and it seems to me that the answer to your question

So this sort of phenomenon occurs because thats how it is interpretted by the homunculus. So the organization of the humunculus ( and the nerves) leading to it) is main reason why this phenomenon occurs, right?

is "No".

The reason I suggest this is that I don't think the homunculus has an "interpretive" function. I do think that it has inputs and outputs which help shape what ends being experienced by a person.

[anoopbal]

Okay, this is my line of thinking.

The nerves goes up to the brain and signal the brain and leave it up to the brain to bring pain. But how does the brain knows which nerves is innervated to whicch body part to bring pain unless there is a virtual body map in the brain? And I assume homunculus is that map. ANd I am assuming thats how the homunculus is invoved (one role I guess) in pain.

Anoop

[Jason Silvernail]

Well, I think the homonculus is one part of the cortical map that smart people like Melzack, Moseley and Wall talk about when they speak of the Neuromatrix.

If we agree on the following points, I think the business of referred pain becomes easier to understand:
- mechanical or chemical events in the nervous tissue drive nociception from periphery
- tension or hypoxia in some part of the nervous tissue makes other connected parts more vulnerable to the same stimulus
- Nociception is modulated at several sites or "train stations" in the PNS and CNS
- Nociception can be down-regulated by descending efferents
-the pain output can vary depending on the size of the nociceptive signal and it's threat value, the modulation up/down of the signal at any of the PNS/CNS "stations", the personal experience of the patient, the plasticity of the cortical map (which includes, but probably isn't limited to the homunculus), the sympathetic/parasympathetic status of the patient's ANS, and the context of the nociceptive drive

If we agree on those, referred pain becomes a bit clearer, I think.
I can think of many, many patients who describe a pain that started one place, then began to spread after varying amounts of time - especially if they were concerned about it, it didn't resolve, or there were further pain "issues".

What do we think?
J

[Luke Rickards]

It is my understanding that while the processes of central sensitisation (homuncular smudging, neural plasticity, activation of silent nociceptors/ion channels etc) can cause pain to spread from the site of damage, they refer to a different process than the perception of referred pain. There is, of course, some crossover.

Somatic referred pain is caused by the convergence of somatic and visceral afferents through the DRG onto the same segmental level in the cord (Diane, perhaps you can expand a little on the relevence of somites in embryological development here). In the spinal cord there are multiple peripheral inputs converging on a single neuron at a somatic level. Keep in mind that there may also have been cross-talk in the DRG. The brain receives the pool of information from the cord neurons at this level and paints the most logical picture. Sometimes it gets this wrong. Referred pain may not always follow a segmental distribution because the are also extrasegmental inputs from the sympathetic afferents, as well as the odd intradural connection between dorsal nerve roots, particularly in the cervical spine.

The pain and tingling exprerienced when you bang your elbow - the ulnar nerve, actually - has a different mechanism again. Here the sensation is due to direct axonal stimulation and resulting firing of the nerve, rather than somatic tissue referral.

[anoopbal]

Hi Jason

How you been? Are you coming back to US again? Really gald to see you posting.

The brain receives the pool of information from the cord neurons at this level and paints the most logical picture. Sometimes it gets this wrong

My thinking is the brain already has a preexisting body map. So if the neurons stimulate the "leg" on the map, the brain knows, ahh the pain is in the leg. Sometimes as you said there is a convergence of visceral and somatic neurons, and the neurons end up stimulating the "shoulder" on the map instead of the heart. But all this happens bcos of EXISTENCE a body map ( and this map can change in certain cases). I agree there are things happeneing in the peripheral NS.

Ok, If I am wrong, what is the function of Humunculus (or main function) in pain?

Thanks
Anoop

[bernard]

Ok, If I am wrong, what is the function of Humunculus (or main function) in pain?

You're wrong. ;)
Maps are intended to speed up the brain processes and there is at least more than 20 homunculi known in the brain. A map stores events coming from periphery. It helps to create a quicker response than waiting events that come from body => It uses the stored "values".

[Luke Rickards]

The brain has a highly specific representation of sensory information coming from the skin. With 3.52 metres of nerve in every square cm, and probably more in the face, hands and feet (also why the homuncular areas for these are so huge), this is not surprising. Get underneath the skin though, and it's a different story.

Of course the homunculi are important, but keep in mind that they don't receive information directly from the tissue - they receive info from third order neurons in the thalamus, which receives info from second order neurons in the cord, which receives info from first order neurons in the PNS. Somatic referred pain occurs when the homunculii can't work out exactly what happened between the first order neuron and the second order neuron.

[AndrewGovernment]

Anoop,

My understanding was that referred pain has to do with the original embryological source, i.e. the sclerotome.

[Diane]

My understanding was that referred pain has to do with the original embryological source, i.e. the sclerotome.
Not so much, probably, as it turns out..

[AndrewGovernment]

Diane,

Interesting... what is the literature suggesting now, in terms of referred pain origins?

[Diane]

I think your best source at the moment would be Topical Issues in Pain, Volume 5, available from www.achesandpainsonline.com
Louis Gifford, the editor, is a zoologist and by the sound of it, layer to rest of false spinal treatment constructs.

[bernard]

And Louis is member of the site :thumbs_up
lsgifford (http://www.somasimple.com/forums/member.php?u=108)

[AndrewGovernment]

Diane,

I can't open the link... is there a mirror site? Do you have available the article re: spinal treatment constructs?

[Diane]

The link works fine. It's not an article, it's a book.

[JaneS]

Just returning briefly to the phantom pain points;

Phantom pain may be generated from unexpected connections within the homunculus. As I understand it, and supported by visual and auditory perceptions, the lack of expected input plays a very significant role in phantom pain. For example, we are used to receiving input from upper limbs, tactile, thermal, proprioceptive. In the case of amputation or total severing of a nerve supplying the upper limb, the neuromatrix still awaits input to interpret and respond.
As a result of lack of neural input, 2 possible consequences are ectopic impulses generated from the periphery in the region of the amputation. The other is the cortical expectation of such impulses. Lacking usual stimulus from one area, the brain may anticipate input and interpret the absence of 'normal' input as a sensation for which there is no external origin. If this internal perception is strong enough, it is reported as pain. Pins and needles, sensation of being covered by a glove and others may be reported by the patient.

Another possibility (not to say that both can't occur simultaneously) is crossmodal interactions. Input from nerves relaying one sense may be carried by adjacent nerves. En route to the cortex, ascending sensory pathways travel closely together in places. There is also a 'polysensory' pathway, which can receive input from other senses. In this area, there is also the possibility that the afferent pathway for an amputated or denervated area may take on and transmit other tactile/nociceptive impulses originating from other external origins.
Therefore, sensation interpreted as coming from the denervated area/stump may have no known external cause or seem to come from other inputs, even from other senses.

Just a comment on references. The information above is drawn from 8-9 references used in my review on neuropathic pain and tinnitus - includes Melzack, Moseley and others. I won't list them all here unless requested.

Jane

[anoopbal]

You're wrong.

Maps are intended to speed up the brain processes and there is at least more than 20 homunculi known in the brain. A map stores events coming from periphery. It helps to create a quicker response than waiting events that come from body => It uses the stored "values".


Thanks Bernard. I am getting used to being wrong in here :)

I am getting cofused here. My info comes from this aticle. Let me know what you think of it. And I am not saying the article is right. I think the article can better convey what I am trying to say.

http://www.behavmedfoundation.org/pdf/paincauses.pdf.

Anoop

[Diane]

Another thing about homunculi that I forgot to mention earlier, and I see Jane didn't mention either.. there's a movement component lacking with phantom pain. Wall said that resolution of pain requires a "consummatory" movement. (He likened pain to a need state, like thirst. When thirsty the consummatory action is to consume fluids... when in pain the consummatory action is to consume movement.)

However, when there is nothing to move, what can the patient do? I imagine a struggle goes on between the motor homunculi and the sensory homunculi.

The mirror box treatment provides the visual cortex with the illusion of movement, which is enough to get the brain off the square it is on. At least a little, for a little while.