Since the 1940s, amputees have managed to qualify as sprinters for the globally recognized Paralympic games. Phantom limb pain (PLP) is a condition approximately 80% of amputees experience (Chahine and Kanazi 2007, Knotkova et al. 2012). [1] Phantom limb pain differs to the term phantom sensation: the ‘pain’ is experienced by the amputee as either burning, crushing or constant stabs of shock, whereas the sensation, refers to itching or cramping at a region of where the limb was found, but this does not cause physical harm to the patient. The causes underlying phantom limb pain are still vague. Despite reports suggesting the neurological condition has a biological pathology, the question that is still proposed is: to what extent can phantom pain be explained by René Descartes’s ghost in a machine theory or is it certain the condition has a biological basis?
Biological explanations suggest there are around three major causes of phantom pain. There are peripheral issues that arise from supposed damaged nerve endings severed from amputation. These include cramping-muscle tension in the residual limb, burning sensation-that implies a vascular issue is present, and shooting-which is caused by ectopic discharge from the stump neuroma or is induced by triggers such as stress. Spinal cord implications are the second reason, where the phantom pain originates from the increased neuronal activity in the spine due to severed nerves.
Researchers believe the main cause of phantom pain is a cortical reorganization, which suggests that areas of the brain correspond to certain amputated areas after amputation link to other regions of the body that are still present. This was proposed by Ramachandran (1993) [2] after a magnetoencephalography scan of a patient revealed that the representation of their face was invaded by the hand region. [3] The sensory nervous system is known as the somatosensory system, where sensory neurons and pathways are connected to various receptor cells in primates, including humans. The mapping of the body surfaces in the brain is called somatotopy. [4] This mapping process means that sensory information from the hand, for example, projects to one cortical site in the brain, whereas from the foot another cortical map is targeted. Now, once a limb has been amputated, cortical remapping/redistribution occurs. Here the sensory input to the brain's primary sensorimotor cortex from that region is non-existent. As a result of this, the cortical site of the amputated limb is no longer relevant and thus a remapped area should be formed from dominating adjacent cortical sites. Studies such as Moseley and Flor (2012), [5] found that neuropathic and musculoskeletal pain is associated with this form of cortical reorganization, especially in the somatosensory cortices.
Plasticity was defined by Dr. Alvaro Pascual-Leone in 1961 as the process that leads to development and learning, the cause of the disease (through hyper plasticity) and a mechanism of functional recovery. Maladaptive plasticity, on the other hand, is the inability of the cortical sites to adapt to this stimulus in the CNS (Central Nervous System), which may cause phantom pain. The hypothesis of maladaptive plasticity predicts that the loss of sensory input from this deprived area of the primary sensorimotor cortex becomes responsive in relation to neighbouring cortical areas. The sensorimotor cortex processes touch and movement. This means that the representations of the amputated limb are reduced in this deprived area. The process triggers greater remapping and reorganization in the adult brain. It is thought to cause a mismatch between information from limbs and other signals which are related to the original affiliation of the area. This results in an error signal that is interpreted by the brain as pain, arising from the missing limb. This concept has been supported by multiple studies using converging techniques and reliable experimental support for the biological cause of this condition.
However, Makin et al. (2015) [6] found that greater pain in amputees correlated to greater preservation in the representation of the amputated limb’s cortical site, as seen in fMRI scans. Whereas the maladaptive plasticity hypothesis would have suggested that greater cortical reorganization would lead to phantom pain. Moreover, contradicting the theory of maladaptive plasticity, investigators found that "greater chronic phantom pain correlated with the degree of activation within the hand cortex, and maintenance of its structural integrity."[7] Amidst the praise for Makin’s paper from leading proponents and neuroscientists, some still suggest that the study does not answer the vital question: whether cortical representation of the amputated limb is maintained by pain signals or is it maladaptive plasticity?
"From the world of the primitive animist, in which we are, in Wendell Berry's words, 'holy beings living among other holy beings in a world that is itself holy', we have arrived at a world in which we are mechanical beings, living among other mechanical beings, in a world that is itself a gigantic machine.” [8]
Phantom pain is currently thought to be driven by brain changes in terms of body representation, triggered by the loss of sensory input from the missing limb. To this debate, however, there is a theological element involving the ancient mind-body problem of dualism. This concept was theorized by René Descartes, where he suggested that the brain and the nervous system acted as a pump with fluid movement that regulates motion, almost like the mechanics of machines. It was later adopted by the British philosopher, Gilbert Ryle. He explained that mental activity can carry on in parallel to physical action [9] through his "Official Doctrine of Cartesian Dualism" in his book the Concept of the Mind published in 1949. [10] For this debate, the theory is interpreted as being able to move away from a painful sensation in our nervous system (machine) where our conscious experience lives the pain outside of our nervous system (ghost). His famous quote, “I think, therefore I am,” [11] suggests that humans may be composed of consciousness, alongside the framework of our bodies of our intricate nervous system.
The key essence encapsulated in this theory is the idea of ‘conscious, subjective experience’, which is not functionally definable, especially since ‘consciousness’ is a unique nervous system process that isn’t supported by animal models. Supposedly, recent research in the year 2016 states that mystical states of unitive experience correspond to measurable activity in terms of electrical impulses in certain parts of our brain. This explanation of our consciousness and soul's ability to feel pain can be recognized through the attention schema theory. Here’s how a brain with an attention schema would function:
Initially, there would be a center of nuanced control attention -- our attention schema. If it had the ability to translate internal information originally stored into words, it would form "strange, physically incoherent claims based on that attention schema."[12] Instead of assuming that the cerebral cortex has formed an attentional enhancement of the visual signal in front of them, our brain would form a non-physical experience of that object using the incomplete information of the object within its attention schema. Hence, consciousness. [13]
It’s a theory that has been developed in order to explain why we convince ourselves with such certainty that we have subjective and in terms of PLP, painful experiences. Attention to objects, situations, memories are fundamental to most animals and to help control it, our brain has evolved an attention schema. Now, consciousness is established as phantom attention and explains why some argue that there may be a "ghost in our machine(s)”. Therefore, perhaps Lord Nelson was right when he suggested that a phantom arm is made up of the same stuff as the soul itself since it’s the information within our brain. Yet the principle is entirely false and based on very little detail. It also poses a categorical mistake where it represents the facts of mental life as if they belonged to one logical type or category when they actually belong to one another.
Various forms of therapy for phantom limb pain in patients have been developed. Mirror visual feedback is the leading form of therapy that was devised in 1994 by V.S. Ramachandran. It was created to help victims with paralysis alleviate pain in non-existent limbs. The patient places a mirror in between the affected and non-affected limb so that the one’s brain is tricked into believing that the affected limb can move. This form of therapy was directly focussed on the neuroplasticity of the brain. Treatments, both pharmacological and non-pharmacological have been developed using biological explanations for this condition. On the other hand, no therapies have been developed for PLP using the "ghost in a machine" theory. Yet, we cannot dismiss the thought that Homo sapiens have a soul since all theological principles are only dismissed once proven wrong by scientific theories and empirical evidence. And since Makin et al.’s research does not answer the essential question of whether PLP can be biologically explained in depth, there is still no accurate explanation. Ultimately, I believe that phantom pain has a biological cause purely based on the vast array of evidence that supports the condition of having a mechanical and chemical pathology.
Work Cited:
2. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC47787/
3. https://academic.oup.com/brain/article/137/3/757/394250
4. https://en.wikipedia.org/wiki/Somatosensory_system
5. https://www.bodyinmind.org/wp-content/uploads/Moseley-Flor-2012-Neurorehab-Neural-Rep-targeting-the-brain-in-rehab-review.pdf
6. https://www.painresearchforum.org/news/25670-new-challenge-maladaptive-plasticity-theory-phantom-limb-pain
7. Ibidem
8. https://charleseisenstein.net/books/the-ascent-of-humanity/the-ghost-in-the-machine/
9. Ryle, Gilbert, "Descartes' Myth," in The Concept of Mind, Hutchinson, London, 1949-wiki
10. https://prezi.com/m4dyc2uh2gzn/gilbert-ryle-ghost-in-the-machine/
11. Ibidem of footnote 4
12. https://www.theatlantic.com/science/archive/2016/02/phantom-limbs-explain-consciousness/459780/
13. Ibidem
About the Author:
Sanjay Babu ’19 is a Biomedical Sciences Student at Queen Mary University of London. He has a desire to pursue a graduate degree in Medicine. He has participated in numerous UKMT Olympiads & outside of his academics, he enjoys swimming, reading, playing the violin and rock climbing as his creative outlets.
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