Interesting article that relates to a paper that was published online in Pain.
“In a way, the debate about the origin of phantom limb syndrome is a version of the ancient mind-body problem,” said professor Marshall Devor of the Hebrew University of Jerusalem’s Department of Cell and Developmental Biology and Center for Research on Pain, who led the study. “Our research resolves the problem, at least in this case. It’s the body.”
The ghost in the machine
Skeptical of conventional brain-centric explanations of phantom limb syndrome, Devor and his colleagues set out to test another neurobiological theory: that phantom limb syndrome comes from the nerve fibers that used to run to the amputated limb. Guided by medical imaging, the researchers injected 31 leg amputees who suffered from phantom limb syndrome – 16 in Albania and 15 in Israel – with local anesthetic near where the nerves from their amputated legs enter the spinal cord in the lower back.
Within minutes, phantom limb sensation and pain was temporarily reduced or eliminated in all the amputees. Control injections had no effect; nor did numbing nerves in the stump in the few cases tested.
Body over mind
“The dismantling of phantoms via the silencing of these ‘terror cells’ is in my mind a death blow to the brain theory of phantom pain and a call to industry to join forces with scientists to find new treatments for neuropathic pain,” said Dr. Haim-Moshe Adahan, who ran the Israeli trial at Chaim Sheba Medical Center at Tel Hashomer’s Pain Rehabilitation Unit and is working on a follow-up study to extend symptom relief using steroids.”
These are bold claims indeed. The final quote above from one of the researchers is certainly very strong with it’s reference to the “death blow to the brain theory of phantom pain”. But the ‘terror cells’ (what a terrible phrase to use) can’t produce pain – they can only send erroneous nociceptive signals to the brain, but what about the idea that “nociception is neither sufficient nor necessary for pain”? Do these results suggest sufficiency of nociception for pain?
The actual paper published in Pain was not quite so strident in its discussion of the findings.
“Our data are inconsistent with maladaptive cortical plasticity being the primary driver of PLP and npPLS. However, some of the secondary peculiarities of phantom limb sensation (eg, telescoping and reference) may well reflect plasticity of cortical processing. Had the impulses interpreted by a conscious brain as PLP originated in the cortex, spinal and intraforaminal blocks would have been ineffective and certainly not topographically appropriate. Beyond that, the very foundations upon which the cortical plasticity hypotheses rest are equivocal.
We propose that ectopic PNS discharge, primarily that originating in DRG serving the amputated limb, drives CNS somatic representations to generate a conscious percept of the phantom limb. The quality of the sensation, PLP or npPLS, presumably depends largely on the types of primary afferent neurons that contribute to the ectopic barrage”
There are a number of very strong dualisms at play here – mind/body, brain/body, peripheral nervous system/central nervous system, top down/bottom up. The whole dualistic argument just evaporates though if you consider one continuous nervous system without arbitrary slash marks separating peripheral from central and one whole human being with an embodied mind embedded in an environment and culture. Then we can say with certainty that bodies don’t have phantom limb pain, brains don’t have phantom limb pain and minds don’t have phantom limb pain – only people experience phantom limb pain.