For people missing an arm or a leg, a sophisticated artificial limb can do more than simply restore some of their capabilities. A report in the June issue of Nature Neuroscience suggests that a so-called "myoelectric prosthesis" - which captures the electrical signals of the muscles in the stump to drive an artificial hand - can prevent phantom pain, feeling that a member hurts, even if it has disappeared.
Almost all patients who undergo amputation can still feel their missing limb during the first weeks after the amputation, and often . missing arm or leg hurts in two of the patients, the pain persists for years or decades the source of phantom pain is enigmatic, but appears to involve rewiring of the cortex, the superior control center of the brain. neurons of the neighboring regions in the cortex seem to establish links with the area which formerly controlled the cut branch, but is now fallow. sensory stimulation of a body part on the other hand, is known to extend the zone the cortex involved in its control.
In a myoelectric prosthesis, electrodes sense, muscle contractions and send electrical signals to a motor driving the movements of the hand. Neurologist Martin Lotze and his colleagues at the University of Tübingen, Germany, wondered whether tactile stimulation as a prosthesis provides or requires muscle activity could prevent expansion in the cortical center used by a neighboring region, control the movement of the lips, and reduce phantom pain.
team interviewed 14 patients on the severity of their pain and their use of the prosthesis. To assess cortical rewiring, they asked the patients to purse your lips, while brain activity in their lip-control region was measured using imaging functional magnetic resonance. Although almost all patients recalled having phantom pain immediately after the amputation, the team found that five patients who wore their functional prosthesis for longer periods and used the most were more or less painless, and showed almost no expansion of the area control lip into the cortex.
Psychologist Ronald Melzack of McGill University in Montreal, Canada, welcomes the work. "These are good things," he said. "There is no doubt that the use of prostheses should be initiated as soon as possible," he said, because it could spare patients from having to take strong painkillers with potentially serious adverse effects. Melzack adds, however, that the myoelectric devices are very sophisticated yet "a very expensive luxury treatment" for amputees.
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