Phantom limb pain (PLP) is a common sequela to amputation. The majority of amputees report pain, often very severe, which seems to emanate from the missing limb. A growing body of evidence suggests that PLP is associated with maladaptive neuroplastic changes in the sensorimotor cortices. When cortical tissue that used to represent the missing limb ceases receiving input from that limb, the tissue from neighboring cortical areas, which represent other body regions, migrate into the area that previously represented the missing limb. Since the face is represented in cortical areas adjacent to the hands and arms, cortical representation of the face migrates into the area that previously represented the amputated limb.
But why should this cortical reorganization lead to pain? One leading hypothesis is that with deaffertation there is a mismatch between motor output and sensory input. The brain sends signals out to the muscles but does not receive the expected feedback. There is a mismatch between motor output and sensory feedback.
What would seem to be needed, then, is some way by which alternative feedback could be presented to convince the brain that he or she can control the limb and that it is responding normally. The problem, of course, is that the patient has no limb to move. That’s where the mirror box comes in.
The mirror box has two parallel compartments with a vertical barrier between the compartments. A mirror surface lines one side of the vertical barrier. The PLP patient places the intact hand on the reflective side of the mirror such that viewing the intact hand in the mirror lends the impression that the missing limb has been “resurrected”.
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