The investigators will use conventional brain fMRI imaging in servicemen and women who undergo mirror therapy to reduce phantom limb pain from their amputated leg, to determine how this therapy reduces the pain and remodels cortical organization in the brain.
Following limb amputation, most patients continue to experience the presence of the missing limb, a sense of being able to move it, and pain emanating from it (phantom limb pain). The investigators recently demonstrated that phantom limb pain can be reduced by having the patient look at a mirror that reflects back to them the image of their intact foot, while they try to move their amputated foot. This therapy was more effective than either using a covered mirror or asking the patient to mentally visualize moving their phantom foot.
A few studies have found a relationship between phantom limb pain severity and degree of reorganization within the motor and sensory cortex in people with arm and hand amputations. Do similar changes occur in people with severe phantom pain from an amputated leg or foot and, if so, where are the new brain cell connections formed in response? The investigators hypothesize that direct input form the visual cortex modulates phantom limb pain by reducing cortical reorganization.
The investigators will use fMRI imaging to study how visual input during the course of mirror therapy can modulate pain severity and how pain reduction relates to cortical reorganization. First, they will use fMRI in 42 patients to visualize brain activation while they perform simple visual and motor tasks in order to learn how body maps in the motor and sensory areas of the brain change following leg amputation and to determine the association, if any, between brain reorganization and phantom limb pain. Then, they will monitor changes in brain activation patterns in the sensory and motor areas while patients undergo four weeks of mirror therapy. They will assess how visual input modifies (reduces) phantom limb pain through reorganization of sensory and motor brain areas, and determine whether pain reduction is associated with reduced reorganization within these brain areas.
Significance: The studies are anticipated to produce better understanding of the physiological interactions between phantom limb pain, visual input, and cortical reorganization, and lead to objective measures of treatment effectiveness and potentially to development of new, more effective, therapies to reduce the pain.