An article published yesterday on Scientific American’s Web site deals with a phenomenon that underscores just how many ways an especially advanced mammalian forebrain can misfire, and and this case the consequences are far more dramatic, and overtly pathological, than the presentation.
In [body integrity and identity disorder] (BIID), or apotemnophilia, individuals say that a limb, or part of it, feels “intrusive” or “over-present.” They usually report that they have had the desire to remove the limb since early childhood, but do not understand why. This desire can be so strong that they sometimes resort to damaging the limb irreparably, thus forcing doctors to amputate it. Almost all BIID sufferers have no other psychological disturbances, and almost always say that they feel much happier when the limb is eventually amputated.
Insanely, this kind of behavior has hitherto been regarded as perhaps faddish or at least self-indulgent:
Voluntary amputation, for example, [has been] regarded as a fetish, perhaps arising because an amputee’s stump resembles a phallus, whereas imaginary extra limbs were likely to be dismissed as the products of delusions or hallucinations.
Things are changing in the neurological community.
Paul McGeoch of The Brain and Perceptual Process Laboratory at the University of California, San Diego, and his colleagues tested the hypothesis that BIID occurs as a result of abnormal activity in the right SPL. They recruited three male BIID sufferers (apotemnophiles) who expressed a desire to have their left leg amputated, and a fourth who wanted both legs removed. The researchers tapped the participants’ feet with a bundle of fiberoptic filaments, while recording the electrical activity of their brains using magnetoencephalography (MEG). Their responses were compared with those of four controls.
In the controls, tapping either foot caused activation of the right SPL. In the three apotemnophiles who wanted one leg amputated, tapping the unaffected foot evoked a response in the right SPL, but tapping the affected one did not. In the fourth apotemnophile, neither foot evoked a response. These findings, which are published in Nature Precedings, confirm the researchers’ hypothesis. They suggest that the brain does not register the limb as a part of the body, and contains no representation of it. As a result, the limb is not incorporated into the body image, so the apotemnophile has no sense of ownership over the limb–he feels that it does not “belong” to him, and so wishes to have it removed.
The Atlantic Monthly published an article about this over eight years ago. The medical findings and the response of scientific minds to them are fascinating in both the more recent piece and the one from a half-decade ago.