Three people who had planned arm amputations retained vivid sensations of a missing limb, often perceiving the arm's presence and attempting to use it. MRI comparisons before and after amputation revealed that phantom hand representations matched pre-amputation hand maps even up to five years after surgery. The preserved somatosensory cortical maps challenge prior views that loss of sensory input causes large-scale cortical reorganization. One amputee had to retrain her behavior to avoid reflexively using the absent limb because the phantom perception prompted instinctive protective actions. The persistence of limb-specific brain circuitry suggests long-term viability for brain-computer interfaces to decode intended movements for prosthetic control.
A rare circulatory problem required Emily Wheldon to have her left arm amputated three years ago. Her brain still thinks it's there. "Most days, it just feels like I've got my arm next to me," she says. The perception is so compelling that Wheldon had to train herself not to rely on the missing limb. "When I first had the amputation," she says, "I was trying to put my arm out to stop myself from falling."
Brain scans showed that in all three, "the phantom hand representation is exactly similar to the pre-amputated hand representation," even five years after surgery, says Hunter Schone, a postdoctoral associate at the University of Pittsburgh who started the project as a doctoral student at University College London. The finding, which appears in the journal Nature Neuroscience, challenges decades-old research in monkeys and people suggesting that after losing sensory input from a limb, the brain dramatically reorganizes the areas linked to that limb.
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