Phantom sensations following acute pain.

In human amputees with painful phantom sensations, mislocalizations of tactile stimuli to the phantom increase with the amount of cortical representational reorganization and the extent of phantom pain. A similar phenomenon was incidentally encountered in healthy subjects. For reasons unrelated to the question of mislocalization, we performed a study involving the application of experimental acute pain to the hand followed by non-noxious tactile stimulation of the ipsilateral lip. During lip stimulation, two out of six subjects spontaneously reported perceiving an additional phantom-like sensation in the hand synchronously to the non-noxious lip stimulation. Similar, although more diffuse, phantom sensations were observed in two out of seven additional subjects who were then tested specifically for this effect. The observation is compatible with a pain-induced hyperresponsiveness of the cortical hand area to somatotopically adjacent inputs from the lip. This suggests that, even in the absence of deafferentation, pain can lead to a representational reorganization.