I guess seeing the movie Farenheit 9/11 brought this question to mind. There was a man who lost both his arms below his elbows and he was explaining that he still felt the pain from them being crushed. Is it the memory of the pain that they are feeling?
Altho a person may lose a limb or two, his neural connections remain unaffected. That portion of his brain that “feels” sensations in the right leg, for example, is not receiving any signals from that leg, so neighboring areas of that brain’s section transmits signals to that section which are translated as pain in the missing limb.
How long does the pain usually last?
I have a friend who lost a leg in ‘Nam, and wears a prosthetic limb. He says that for a few years after it was fitted, he would get an itch that, realistically, he couldn’t scratch. When doctors explained the ‘neural connection’ mentioned above, he would convince himself that the itch wasn’t physical, and it would stop. Perhaps mind over mind?
Studies in primates [see V.S. Ramachandran–but be wary, his results are yet to be reproduced] prove the hypothesis that phantom limb feeling comes from neural connections in the somatosensory cortex. Evidence shows that these neighboring regions actually rewire themselves to take over the area representing the deafferented limb.
A good example was shown by Ramachandran. After deafferentation of the arm of an adult macaque, pressure on the ‘stump’ caused sensation in the region of the stump, as well as an area of the face, on a regular basis.
This is called phantom pain and is fairly common. Don’t have time to do it myself right now, but I bet google would produce some good hits.