Supernumerary Phantom Limb Confirmed
Physicians at Geneva University Hospital have confirmed what may be the first instance of a supernumerary phantom limb that can be moved, felt and seen by the patient.
The patient had apparently suffered a stroke; the additional phantom limb appeared several days later. Dr. Asaid Khateb of the hospital's experimental neurophysiology laboratory used functional magnetic resonance imaging (fMRI) to check the woman's claims.
In this case, the investigations revealed that the woman actually experienced what she described.
Researchers instructed the woman to move her right hand. As expected, the motor cortex and visual processing areas in the left side of her brain became mobilised.
The same effects were observed to a lesser extent when the woman simply imagined moving her right hand. Imaginary movements of the woman's paralysed left hand prompted the same activity in the brain, but on the right side.
But when doctors asked her to move her phantom arm, her brain reacted as though the arm really existed and could be moved. In addition, the patient's visual cortex was also activated, indicating the she actually saw the imaginary limb.
And when she was instructed to scratch her cheek, regions of the brain relating to touch were activated.
"Existing evidence from stroke-elicited SPLs convincingly implicates the mismatch between the subject's well-established sensorimotor representations and a suddenly aberrant pattern of communication between the brain and the paralysed limb," the authors wrote.
Although the phenomenon of "phantom limbs" has been well-known throughout human history, the name was given in the 1870's by physicians attending the many amputees from the Civil War. Most amputees feel pain or other sensation in their 'missing limb.' In this case, however, the patient has created the idea of an additional, or supernumerary, phantom limb, which is very rare. Doctors have now used fMRI to confirm that the patient truly feels as if she has an additional limb that can interact with the rest of her body image.
The finding has been published in the Annals of Neurology.
Interesting work is being done using MRI technology to actually visualize the brain's contents; take a look at Spatial Memories Seen In Hippocampus fMRI.
Although this is not a predictive sf idea, fans recall the psychic arm of Gil Hamilton from the Known Space universe stories created by Larry Niven (I think that Death by Ecstasy  was the first). Gil Hamilton loses his right arm in an asteroid mining explosion; he eventually develops a spectral "arm" able to manipulate the external environment.
From Doctors confirm woman's imaginary third arm; thanks to Chris Johnston for sending in the tip and the reference.
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