Many amputees have a sense of their missing ‘phantom’ limb1,2,3. Amputation can alter the representation of the body's surface in the cerebral cortex4,5,6,7,8,9,10,11,12,13,14 and thalamus15,16, but it is unclear how these changes relate to such phantom sensations. One possibility is that, in amputees who experience phantom sensations, the region of the thalamus that originally represented the missing limb remains functional and can give rise to phantom sensations even when some thalamic ‘limb’ neurons begin to respond to stimulation of other body regions. Here we use microelectrode recording and microstimulation during functional stereotactic mapping of the ventrocaudal thalamus in amputees to determine both the responses of the neurons to stimulation of the skin and the perceptual effects of electrical activation of these neurons. Thalamic mapping revealed an unusually large thalamic stump representation, consistent with the findings from animal experiments. We also found that thalamic stimulation in amputees with a phantom limb could evoke phantom sensations, including pain, even in regions containing neurons responsive to tactile stimulation of the stump. These findings support the hypothesis that the thalamic representation of the amputated limb remains functional in amputees with phantoms.
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We thank F. Lenz for assistance with data collection from two of the patients; M.Teofilo for technical assistance with computer reconstructions of patient data; and A. D. Craig and J.Katz for comments on an earlier draft of this manuscript. This work was supported by the Medical Research Council of Canada and NIH.
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