Simply put, movement begins in the brain. A command is sent through the nervous system to the muscles telling them to move in a certain way.
In physical therapy, one is told to move the legs or hands. The patient then mentally sends a command to the legs or the hands to tell them to move. However, since the nerves have been damaged, the message does not go completely through because of the physical damage and the muscles do not respond because the message does not reach the muscles because of the nerve damage.
In normal people, the movement of the fingers and legs sends a “feedback” to the brain informing the brain: “Command executed, I am moving”. When the brain sends another command to the moving hands and legs to tell them to stop, the hands and the legs stop their movement, as in walking and stopping, and the arms and legs send a “feedback” to the brain telling the brain: “Yes, I stopped.”
The brain is aware of hand and leg movements as one is aware of walking. The brain is also aware of hand and leg movements that have stopped as one is aware of stopping and standing still like walking up to a pedestrian crossing and stopping to wait for the “walk” sign to turn green.
The movement generates this feedback and sends it back to the brain via the nervous system. This feedback initiated by the movement stimulates regeneration of the damaged nerves.
Phantom limb pain is a neuropathic pain, and according to The Merck Manual of Medical Information (Page 316), the pain is “caused by the nerves above the site where the limb was amputated. The brain misinterprets the nerve signals as coming from the amputated limb.”
In a sense, the brain “remembers the pain at the time of trauma” when the trauma severed the limb and the nerves in it.
A doctor was able to “fix” the phantom limb pain by tricking the brain into thinking that the severed limb is “still there”. In the demonstrated case, a man had a severed right hand. So he was told to sit down in a booth which had a mirror on the right side. The patient was told to place his left hand on the desk top so that it is reflected in the mirror. When he moved his fingers of his good left hand, the reflection also moved as if he had a good right hand and fingers that moved.
This physical therapy calmed the neuropathic pain.