phantom limb illusion

   Also referred to as phantom or phantom limb. The term phantom comes from the Greek noun phantasma, which means ghost or spectre. The terms phantom and phantom limb refer to an arm or a leg, the presence of which is perceived although the limb itself is absent. One of the earliest known descriptions of a phantom limb illusion stems from the French surgeon Ambroise Paré (1510-1590), who published a case study in his 1511 treatise on gunshot wounds. Clinically, a phantom limb illusion can occur in individuals missing one or more limbs, either congenitally, or following an amputation. Following an amputation, up to 95% of the affected individuals may experience a phantom limb manifesting itself as a pleasant, tingling sensation. In addition, clinical research indicates that 50-80% of all amputees experience transient or permanent * phantom sensations in their amputated limb, mostly in the form of * phantom pain. The group of phantom sensations includes feelings ofpain, pressure, warmth, cold, itching, burning, vibration, and hallucinated posture. Phantom sensations may also occur after the removal of body parts other than the limbs, i.e. after the amputation ofa testicle, extraction of a tooth (as in *phantom tooth pain), or enucleation (as in *phantom eye syndrome). Phantom limbs often feel incomplete, or shorter in length than the limbs actually were, prior to the amputation. It has been suggested that the sudden loss of a limb or other body part is more likely to entail a phantom limb illusion than does a gradual loss, as in leprosy. A variant of phantom limb in which more than one non-existing arm or leg is perceived is called * supernumerary phantom limb. Traditionally, the dominant theory for the neurophysiological correlate of phantom limbs has been based on the alleged involvement of neuromata at the ends of severed neurons within the remaining stumps. According to this peripheral hypothesis, the neuromata are responsible for generating random afferent signals that are subsequently interpreted by the CNS as pain. Since 1998 a competing hypothesis, put forward by the American neuro-scientist Vilayanur S. Ramachandran (b. 1951), has been gaining influence. This hypothesis, called the central deafferentiation hypothesis, involves the primary involvement of cerebral cortical reorganization. The validity of this hypothesis has been indicated by neuroimaging studies which suggest that cortical reorganization does indeed occur after amputation of a limb and that the degree of phantom limb pain would seem to correlate with the extent of cortical reorganization. In 1934 the term *algohallucinosis was introduced by the Belgian neuropathologist Ludo van Bogaert (1897-1989) as a generic term for the notions of phantom pain and phantom limb.

   References

   Fisher, S. (1962). Body image boundaries and hal-lucinations.In: Hallucinations. Edited by West, L.J. New York, NY: Grune & Stratton.

   Jones, L.A. (1988). Motor illusions: What do they reveal about proprioception? Psychological Bulletin, 103, 72-86.

   Paré, A. (1551). La méthode de curer les combus-tiones principalement faictes par la pouldre à canon.Paris:JeandeBrie.

   Ramachandran, V.S., Blakeslee, S. (1998). Phantoms in the brain: Probing the mysteries ofthe human mind. New York, NY: Quill.