Body Part Phantoms

The occurrence of body part phantoms was among the first and continues to be among the most impressive arguments for the contention that a predetermined body image underlies and modifies the way we experience our own bodies.

The basic experience of body part phantoms is somatosensory: A body part is felt to exist, although it is either absent or cut off from the cerebral cortex by peripheral, spinal, or subcortical interruption of somatosensory afferences. Phantoms have been reported for nearly every part of the body but are most frequent and best explored for limbs and female breasts.

1. Somatosensory Influences on Phantom Sensation

It has long been established that touch of the stump can evoke referred sensations in phantoms of amputated limbs, but only recently it has been shown that referred sensations can originate in body parts that have no anatomical proximity to the amputated body part. In patients with upper limb amputations referred sensations have been evoked from both sides of the chest, both sides of the face, and the contralateral arm. Sensations in phantoms of amputated breasts have been evoked by touch of both sides of the back and the ipsilateral pinna. The presence, extent, and localization of referred sensations vary greatly between patients. In some of them, an exact and reproducible topographical remapping from stimulated to referred locations has been demonstrated that remained stable for up to several weeks. Reexaminations after longer delays, however, have documented radical changes or even complete breakdown of topographical referral without accompanying changes of the phantom's size and shape.

2. Visual Influences on Phantom Experience

Phantoms of amputated body parts clearly contradict the visual perception of their absence and thus challenge the dominance of vision for awareness of one's body, but evidence for an influence of vision on phantom experience derives from patients with spinal cord transsection. Their limbs are anesthetic and plegic but visibly present. Virtually all these patients have phantom experience of the disconnected limbs. During the first days many patients feel the phantom limbs to be flexed although their plegic real limbs are extended, but within a few weeks the phantom position joins the real position. Because the patients' brains have no somatosensory information about the real limb position, they must use vision of the real limbs for adapting the phantoms.

Further evidence for a visual influence on phantom experience may be deduced from adaptation to prostheses. In patients fitted with prostheses, phantoms frequently adapt to their shape. Similar to normal persons who were induced to feel a distant shoe as being part of their bodies, some amputated patients integrate the prosthesis into their bodies and identify it with the phantom. They feel touch directly at the surface of the prosthesis rather than deducing it from the prosthesis' pressure on the stump. Apparently, vision ofthe prosthesis entertains and shapes the phantom experience and makes possible a meaningful and functionally advantageous stabilization and refinement of sensory remapping from stump to phantom.

Upper limb prostheses seem to have less influence on shape and size of phantoms than do lower limb prostheses, but visual capture of upper limb phantoms has been convincingly demonstrated in a series of elegant experiments by Ramachandran and

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