Novel Phenomenal Experience
August 1, 2000 3 minutes read
Novel Phenomenal Experience
Abstract & Commentary
Source: Brugger P, et al. Beyond re-membering: Phantom sensations of congenitally absent limbs. Proc Natl Acad Sci USA 2000;97:6167-6172.
Every now and then your alert editor feels compelled to comment on a remarkable, novel neurological experience that brings new understanding about how the brain works, but for which no therapy is possible. Such follows.
Most neurologists have encountered the phenomenon of a phantom limb, an inner memory that remains in an amputee’s mind following removal of an arm or leg due to trauma or medical disease. Only a few patients, however, have been recorded in whom severe prenatal losses of limbs have been associated with cerebral conceptualization that normal members remain. Thus this anecdote.
An intelligent, well-educated woman, age 44, was born with symmetrical near-absence of all four limbs. As an adult, her upper limbs measured about 25 cm long and consisted of bilateral conically shaped humeri inserted into normal shoulder sockets. The latter arrangement permitted full proximal arm movements. Rudimentary thighs measuring 10 cm extended from dysplastic hip articulations. Despite these limitations, she correctly uses many common, day-to-day objects, typewrites with her arm stumps, and writes with her mouth. For her entire life she has mentally perceived the presence of complete forearms and lower limbs. Only a direct gaze or a mirror provides her with awareness of her normally felt members. She vividly conceived positions of her absent hands or lower extremities when presented with appropriate tasks that would normally require specific, relatively fine manipulations or lower leg-foot activities. Physiological testing indicated normal distal reaction times in the limb stumps and explicitly copied the action times that would be present with normal manipulations. Functional magnetic resonance imaging (fMRI) identified manual task-engendered bilateral activation of dorsal and mesial premotor regions (supplementary motor cortex) as well as superior posterior parietal cortical areas. Hand and finger representation areas in the primary motor cortex were silent. Self-perceived, conceptual activation of phantom flexion-extension foot movement activated normally placed, appropriate regions in contralateral premotor and parietal areas. Motor area 4 expressed only minimal activity on either side. Transcranial magnetic stimulation (TMS) evoked large areas of detectable deltoid muscle activity and also induced phantom movement sensations in the contralateral member after latencies of more than one second.
Commentary
This is the first detailed scientific report to confirm in the brain the origins of phantom limb perception of abnormal cerebral physiological patterns associated with congenitally absent limbs. 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. A third is that only a few cases of congenital aplasia appear to exist, none with satisfactory explanation. (A mini-epidemic of such developmental defects was associated with the drug thalidomide, an agent that appeared during the early 1960s. It seems possible that the drug might relate to this woman’s tragedy.) 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. —fred plum
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