Pain 'memories' in phantom limbs: review and clinical observations

This paper reviews reports of phantom limb sensations which resemble somatosensory events experienced in the limb before amputation. It also presents descriptions of this phenomenon in 68 amputees who took part in a series of clinical studies. These somatosensory memories are predominantly replicas of distressing pre-amputation lesions and pains which were experienced at or near the time of amputation, and are described as having the same qualities of sensation as the pre-amputation pain. The patients who experience these pains emphasize that they are suffering real pain which they can describe in vivid detail, and insist that the experience is not merely a cognitive recollection of an earlier pain. Reports of somatosensory memories are less common when there has been a discontinuity, or a pain-free interval, between the experience of pain and amputation. Among the somatosensory memories reported are cutaneous lesions, deep tissue injuries, bone and joint pain and painful pre-amputation postures. The experience of somatosensory memories does not appear to be related to the duration of pre-amputation pain, time since amputation, age, gender, prosthetic use, level of amputation, number of limbs amputated, or whether the amputation followed an accident or illness. The results suggest that somatosensory inputs of sufficient intensity and duration can produce lasting changes in central neural structures which combine with cognitive-evaluative memories of the pre-amputation pain to give rise to the unified experience of a past pain referred to the phantom limb. Implications for pre- and post-operative pain control are discussed.