Reorganizational and perceptional changes after amputation

The demonstration of cortical representational shifts in adult animals subsequent to deafferentation from amputation or dorsal rhizotomy has spurred attempts to elucidate the perceptual correlates of reorganization. Because the hand is flanked by the face and the trunk on the cortical homunculus it has been suggested that cortical remapping in arm amputees leads to a mislocalization of sensations from these sites to the phantom arm in a systematic manner with modality specific one-to-one topographical correspondence. Therefore, we assessed shifts of representational zones by magnetic source imaging in eight arm-amputees and examined them for referred sensation by somaesthetic stimuli of different modalities at standardized sites. It was found that referred phantom sensations can be evoked from sites on the face and the trunk ipsilateral but also contralateral to the amputation and that the extent of physiological reorganization as revealed by magnetic source imaging strongly correlates with the number of sites, be it ipsi- or contralateral, from where painful stimuli evoke referred sensation. Thus, it seems that the extent of reorganization after amputation is closely related to nociceptive inputs. The mislocalization evoked from both sides of the body, suggesting involvement of bilateral pathways, demonstrates that the perceptual changes go beyond what can be explained by shifts in neighbouring cortical representational zones.