PHANTOM SENSATIONS GENERATED BY THALAMIC MICROSTIMULATION

Many amputees have a sense of their missing 'phantom' limb(1-3) Amputa tion can alter the representation of the body's surface in the cerebra l cortex(4-14) and thalamus(15,16), but it is unclear how these change s relate to such phantom sensations, One possibility is that, in amput ees who experience phantom sensations, the region of the thalamus that originally represented the missing limb remains functional and can gi ve rise to phantom sensations even when some thalamic 'limb' neurons b egin to respond to stimulation of other body regions, Here we use micr oelectrode recording and microstimulation during functional stereotact ic mapping of the ventrocaudal thalamus in amputees to determine both the responses of the neurons to stimulation of the skin and the percep tual effects of electrical activation of these neurons. Thalamic mappi ng revealed an unusually large thalamic stump representation, consiste nt with the findings from animal experiments. We also found that thala mic stimulation in amputees with a phantom limb could evoke phantom se nsations, including pain, even in regions containing neurons responsiv e to tactile stimulation of the stump, These findings support the hypo thesis that the thalamic representation of the amputated limb remains functional. in amputees with phantoms.