The Lost Manual: How to Point to Your Pain
The fact is that we all do rely, without hesitation, on "third-person" behavioral evidence to support or reject hypotheses about the consciousness of animals. What else, after all, could be the source of our "pretheoretical intuitions"? But these intuitions in themselves are an untrustworthy lot, much in need of reflective evaluation. For instance, do you see "sentience" or "mere discriminatory reactivity" in the Venus Fly Trap, or in the amoeba, or in the jellyfish? What more than mere discriminatory reactivity- the sort of competence many robots exhibit- are you seeing when you see sentience in a creature? It is, in fact, ridiculously easy to induce powerful intuitions of not just sentience but full-blown consciousness (ripe with malevolence or curiosity or friendship) by exposing people to quite simple robots made to move in familiar mammalian ways at mammalian speeds. Cog, a delightfully humanoid robot being built at MIT, has eyes, hands, and arms that move the way yours do- swiftly, re- laxedly, compliantly (Dennett, 1994). Even those of us working on the project, knowing full well that we have not even begun to program the high level processes that might arguably endow Cog with consciousness, get an almost overwhelming sense of being in the presence of another conscious observer when Cog's eyes still quite blindly and stupidly follow one's hand gestures. Once again, I plead for symmetry: when you acknowledge the power of such elegant, lifelike motions to charm you into an illusion, note that it ought to be an open question, still, whether you are also being charmed by your beloved dog or cat or the noble elephant. Feelings are too easy to provoke for them to count for much here. [BrainChildren, 339-340]
]In the last two decades, however, several experiments on the effects of deafferentation (or amputation) on somatosensory maps in adult primates and other mammals suggest that we may need to revise this conception of the nervous system (Wall, 1977; Kaas et al., 1983; Merzenich et al., 1984; Wall, 1984; Byrne and Calford, 1991; Calford and Tweedale, 1991a, b; Pons et al., 1991; Florence and Kaas, 1995; Florence et al., 1996; Kaas and Florence, 1997). These animal experiments have shown that sensory maps can indeed change in the adult brain, and they have been largely responsible for the current resurgence of interest in the clinical phenomenon of phantom limbs (Ramachandran, 1993b). Taken collectively, the work on animals and human patients provides a valuable experimental opportunity to investigate not only how new connections emerge in the adult human brain, but also how information from different sensory modules, e.g. touch, proprioception and vision, interact. The study of phantom limbs also provides an opportunity to understand exactly how the brain constructs a body image, and how this image is continuously updated in response to changing sensory inputs.The phrase ‘phantom limb’ was introduced by Silas Weir Mitchell (1871, 1872), who also provided their first clear clinical description. Patients with this syndrome experience an amputated extremity as still present, and in some cases also experience pain or cramping in the missing limb. The term is sometimes also used to designate a dissociationbetween the felt position of the limb and its actual position, e.g. as occurs during a spinal or brachial plexus block (Melzack and Bromage, 1973). It is important to note that in all these cases the patient recognizes that the sensations are not veridical, i.e. what he/she experiences is an illusion, not a delusion.Phantom limbs were probably known since antiquity and, not surprisingly, there is an elaborate folklore surrounding them. After Lord Nelson lost his right arm during an unsuccessful attack on Santa Cruz de Tenerife, he experienced compelling phantom limb pains, including the sensation of fingers digging into his phantom palm. The emergence of these ghostly sensations led the sea lord to proclaim that his phantom was a ‘direct proof of the existence of the soul’ (Riddoch, 1941). If an arm can survive physical annihilation, why not the entire person?Since the time of Mitchell’s (1872) original description, there have been literally hundreds of fascinating clinical case reports of phantom limbs. However, there has been a tendency to regard the syndrome as a clinical curiosity, and very little experimental work has been done on it. Contrary to this view, we will argue that a study of phantom limbs can provide fundamental insights into the functional organization of the normal human brain and that they can serve as perceptual markers for tracking neural plasticity in the adult brain. [Phantom Limb]