Phantom limbs: the body in the brain

Aiha Zemp has served as a subject in an extraordinary series of experiments:

In a neuropsychological study, she was shown pictures of hands and feet. With her right stump, she had to press the space bar of a keyboard whenever a right limb was displayed, or with her left stump when a left limb was displayed. The computer measured her reaction times with millisecond precision. Aiha's correct decisions were significantly faster when fingers or toes pointed up in the picture than when the limbs were portrayed under 180° rotation. This pattern is exactly the same as the one shown by control persons, for whom it is well established that they perform a mental rotation of their hand to correctly decide the laterality of a hand pictured fingers down. This mental rotation is a time-consuming process and gives testimony to the existence of an internal represenation of hands including associated functional properties. Quite obviously, in Aiha Zemp's brain there is also such an internal hand representation - despite the fact that hands and feet had never been physically developed. As a next step, functional magnetic resonance imaging (fMRI) was performed while Aiha Zemp was moving her phantom fingers in a scanner. The figure below shows significant activation of cortical areas activated by movements of the fingers of the right hand; remember: these are nonexistent fingers of a nonexistent hand, but nevertheless, the brain does appear to be involved in the programming and "phantom execution" of these virtual movements. The "virtual reality" of phantom limbs seems therefore compelling, even in the case of phantoms of body parts that have never been experienced in any physical sense.
A third method, transcranial magnetic stimulation (TMS) of Aiha Zemp's brain (specifically of those regions known to be responsible for hand motor control) elicited movement sensations in her phantom hand. Together, these neuroscience methods lend support to the assumption that we may well be born with a complete body as long as we are born with a functional brain. The implications of these findings are fundamental: They not only refine neuropsychological accounts of the interconnections between body and mind, but also shed some light on folk-parapsychological conceptualizations of an "astral body" as a duplicate of our physical body. As such they are important for a scientifically founded theory of a large number of phenomena previously enshrouded in occult ideologies (e.g., doppelgänger and out-of-body experiences).

This research was awarded the Pfizer prize for clinical neurosciences in the year of 2001, and the detailed results have been published in the "Proceedings of the National Academy of Sciences of the United States" (P.Brugger, S.S.Kollias, R.M.Müri, G.Crelier, M.-C.Hepp-Reymond & M. Regard: "Beyond re-membering: phantom sensations of congenitally absent limbs." PNAS, Vol. 97, pages 6167-6172). This research report has received considerable attention from a broad variety of scientific disciplines. Writes distinguished neurologist Fred Plum in "Neurology Alert" (August 2000; p. 92): "This is the first detailed scientific report to confirm in the brain the origins of phantom limb perception (…). Several points are brought forth in the discussion. One is that persons experiencing phantoms following traumatic amputations and studied by fMRI retained physiological activity in the primary sensorimotor cortex. A second is that 19th-century studies reported atrophic cerebral gyruses associated with congenitally absent limbs, but fMRI failed to identify such an abnormality in this woman's fMRI (…) Brugger and colleagues made the final, obvious point that phantom perception is not exclusively expressed by older children or adults suddenly deprived of one or more limbs."

Figure Legend: (Bild vom Gehirn) Cortical activation areas during self-paced movements of right phantom fingers in Aiha Zemp while undergoing fMRI. Arrows indicate the anatomical region corresponding to the hand representation in normal subjects. As in normal controls, premotor (above arrows) and parietal (below arrows) areas are involved in movement planning and monitoring, respectively.

Bibliography:

Brugger P, Kollias SS, Müri R, Crelier G, Hepp-Reymond M-C, Regard M (2000). Beyond re-membering: phantom sensations of congenitally absent limbs. Proceedings of the National Academy of Sciences of the United States of America, 97, 6167-6172.

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