The Mind-Body Problem
What does it feel like to have too many arms?
By Moheb Costandi
Scientific American
If people told you that they wanted to have a perfectly good leg amputated, or that they have three arms, when they clearly do not, you would probably think that they are mentally disturbed. Psychiatrists, too, long considered such conditions to be psychological in origin. Voluntary amputation, for example, was 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.
These bizarre conditions—named body integrity and identity disorder (BIID) and supernumerary phantom limb, respectively—are now believed to have a neurological basis, and a growing body of literature suggests that such body awareness disorders occur as a result of abnormal activity in the right superior parietal lobule (SPL). This brain region integrates different types of sensory information and processes it further to generate an internal model of the body. Two forthcoming studies provide strong evidence that the gross distortions of body image experienced in both conditions do indeed occur as a result of SPL dysfunction.
A Useless Limb
In 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.
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.
(More here.)
By Moheb Costandi
Scientific American
If people told you that they wanted to have a perfectly good leg amputated, or that they have three arms, when they clearly do not, you would probably think that they are mentally disturbed. Psychiatrists, too, long considered such conditions to be psychological in origin. Voluntary amputation, for example, was 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.
These bizarre conditions—named body integrity and identity disorder (BIID) and supernumerary phantom limb, respectively—are now believed to have a neurological basis, and a growing body of literature suggests that such body awareness disorders occur as a result of abnormal activity in the right superior parietal lobule (SPL). This brain region integrates different types of sensory information and processes it further to generate an internal model of the body. Two forthcoming studies provide strong evidence that the gross distortions of body image experienced in both conditions do indeed occur as a result of SPL dysfunction.
A Useless Limb
In 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.
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.
(More here.)
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