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First off, I don't know if this is a normal healthy thing to occur. There have been many times where I have an itch on say my arm and I scratch it, only to feel the scratching elsewhere on my body. I assume somewhere along the transit of the touch signals to my brain the signal gets mixed up and is processed incorrectly.

So my questions are:

  • Why does this mixup happen? (chemical imbalance, damaged nerves, etc..)
  • How does my brain correspond the touch to somewhere else? (what is the process behind it)
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You might be interested in this. And this. –  terdon Apr 1 '13 at 17:28
    
@terdon: Thanks for the links, but interesting as they are they don't answer why the touch signals get crossed =o(. Irregardless if it is an itch or another form of touch, the brain should not be interpreting a touch on one part of the body as coming from another part. My question is why this mixup occurs and how the brain is incorrectly processing it. –  cryptic ツ Apr 2 '13 at 11:20
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I know, that's why I posted a comment and not an answer. Just thought you might be interested. –  terdon Apr 2 '13 at 11:48
    
Could you clarify exactly how the sensation is wrong for you? You are supposed to have an itch for whatever reason, and when you scratch it it's supposed to go away and you get the touch sensation of your fingers instead. All in the same place of course. Are you saying that the actual touch sensation of your fingers on your skin is mislocated? If so, is there a regularity to where it is mislocated (e.g. symmetrical to body axis)? And does this only occur on skin that was itching before, or any part at any time? –  Armatus Apr 3 '13 at 17:58
    
@Armatus well the last time it happened I got an itch on the back of my arm and scratched it only to feel the scratching on my lower back. I don't recall which body axis they were at, I'll have to note that next time it happens, but it's rare. No, it does not occur on skin that was itching before. –  cryptic ツ Apr 3 '13 at 18:06

1 Answer 1

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Well nerve crossing or misinterpretation of nerve signal by the brain does not happen all the time. In case it happens frequently then I guess it would be Multiple Sclerosis or might be Fibromyalgia syndrome. In multiple sclerosis, the Myelin sheath surrounding neuron when gets damaged causes certain problem with nerve signal transmission to the brain. But that is not the main cause. The main cause can be found in Neuropathy:

When nerve cells are damaged, perhaps by a temporary restriction in their access to oxygen, they too atrophy or shrink a little, thus the synaptic junctions widens. Just like with a spark plug in your car or lawn mower, if this gap gets too wide, the spark cannot make the jump. A normal sized nerve signal cannot jump this enlarged gap either, so the signal either does not get through or it gets misdirected to another part of the body and is misinterpreted as pain.

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So I can say that the nerve cells in the place where you feel real pain fails to transmit the signal to brain via its neighboring nerve cell instead that signal passes through some other node randomly (or it might take the same path every time you touch the pain area) and signal the brain which gets misinterpreted and make you feel that you have pain in the misinterpreted region.

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