The reality of phantom limbs
This paper evaluates the joint influence of peripheral neurophysiological factors and higher-order cognitive and affective processes in triggering or modulating a variety of phantom limb experiences, including pain. Part 1 outlines one way in which the sympathetic nervous system may influence phantom limb pain. A model involving a sympathetic-efferent somatic-afferent cycle is presented to explain fluctuations in the intensity of sensations referred to the phantom limb. In part 2, the model is extended to explain the puzzling finding that onlyafter amputation are thoughts and feelings capable of evoking referred sensations to the (phantom) limb. While phantom pains and other sensations frequently are triggered by thoughts and feelings, there is no evidence that the painful or painless phantom limb is a symptom of a psychological disorder. In part 3, the concept of a pain memory is introduced and described with examples. The data show that pain experienced prior to amputation may persist in the form of a memory referred to the phantom limb causing continued suffering and distress. It is argued that two independent and potentially dissociable memory components underlie the unified experience of a pain memory. This conceptualization is evaluated in the context of the surgical arena, raising the possibility that under certain conditions postoperative pain may, in part, reflect the persistent central neural memory trace left by the surgical procedure. It is concluded that the experience of a phantom limb is determined by a complex interaction of inputs from the periphery and widespread regions of the brain subserving sensory, cognitive, and affective processes.