Figure 1 Samples of anatomically impossible or abnormal phantoms after upper elbow amputation. (A and B) The hand is disconnected from the stump. (C) The hand is located within the stump. (D) The extreme shortening of the arm is anatomically possible but corresponds to a deformation that had not been present before amputation (redrawn with permission from sketches made by the affected patients, published in W. E. Haber, Observations on phantom limb phenomena. Arch. Neurol. Psychiatr. 75, 624-636, © 1956, American Medical Asociation).

coworkers. They "resurrected" vision of the amputated arm by means of a mirror reflecting the patient's opposite arm or the gloved arm of another person. Movement of the mirror image induced a feeling of phantom movement regardless of whether the patient's or the experimenter's arm had induced the illusion. When the patient's intact arm was touched, patients felt touch at the mirror location on the phantom. This illusion was contingent on the actual application of touch to the intact arm. Seeing touch of the experimenter's hand reflected to the resurrected phantom did not induce a feeling of touch on the phantom. A synchrony between any feeling of touch and vision of phantom touch was necessary for inducing a feeling of touch on the phantom.

3. Phantoms in Congenital Absence of Limbs

The possibility of phantom limbs in persons with congenital absence or very early amputation of limbs has been reliably established, but their frequency is substantially lower than that after later amputation. Permanent phantoms are reported by approximately 10% of persons with congenital absence or very early amputation of limbs compared to approximately 90% of persons amputated after the age of 10 years. The incidence increases to approximately 20% when temporary phantom sensations are considered. Some persons report having had phantoms as long as they can remember, but in the majority phantoms occur only after a delay. The mean time to phantom onset has been calculated to be 9 years in congenital absence and 2.3 years in early amputation. The emergence of the phantom may be triggered by minor trauma to the stump.

Because the affected children had no or only rudimentary opportunity to experience the presence of the now missing limb, the phantom has been said to represent a genetical prefiguration of the mental representation of body shape. However, there is evidence that pre- and postamputation experience can shape phantoms in children. In children with early amputation of congenitally deformed limbs the phantom may replicate the initial deformation rather than restituting a normal limb. This shaping by early experience may contrast with an inability to consciously remember the deformation. Like phantoms of adult patients, those of children can be triggered and shaped by prostheses: Phantoms of congenitally absent or early lost limbs are more frequent in children who have been fitted with prostheses than in those without, and they usually adapt their size and shape to the prosthesis.

4. Anatomically Impossible Phantoms

Over time, the proximal portion of limb phantoms tends to fade. This can lead to the strange sensation of the distal limb being disconnected from but still belonging to the body or to telescoping of the limb (Fig. 1). Telescoping causes a severe deformation of size and shape of phantoms and may result in the anatomically impossible location of fingers inside the stump. Full-sized phantoms may be in unnatural positions violating anatomical constraints. For example, the hand of a phantom arm may penetrate into the chest. There is a report of one girl who, after amputation of her congenitally deformed right leg, developed one phantom adapted to the prosthesis, one reproducing the original deformation, and one consisting of toes fixed to the stump, thus experiencing an anatomically impossible coexistence of three right legs.

5. The Body Representation Underlying Phantoms

The mental representation of one's body underlying the phantom experience seems to be a moldable and fleeting construction aimed at integrating pre- and postmorbid experience, functional affordances, and discrepant sensory afferences. It cannot be reduced to being a replication of a genetically prefigured body image or of the premorbidly intact body shape. It seems doubtful that a genetically predetermined mental representation of normal body shape plays a role in the genesis of phantoms at all. It is difficult to imagine how a predetermined mental representation can force completion of the body image by phantoms of missing parts but cannot prevent deformation of that image by anatomically impossible phantoms.

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