Phantom Pain and Limbs

The loss of an arm or leg through amputation is not an easy experience to endure, and is even more difficult when the patient begins to feel uncomfortable sensations in their now missing limb. This feeling, referred to as “phantom pain” or “stump hallucination”, is a frustrating sensation to an amputee.

For some amputees, these phantom sensations may be no more than painless distractions of pressure, warmth, and cold that do not interfere with their everyday lives. Some patients have even reported having phantom pleasures; an “orgasmic” feeling in a missing limb. For the majority of amputees, about 50% to 80% (Sherman), they experience phantom pains that vary in classification from cramping, burning, tingling, shocking, shooting and stabbing pains. These episodes are severe enough to interfere with work, sleep and normal function, and do require some kind of treatment. Phantom pain can occur anytime, from immediately after an amputation to several years later.

The powerful impression of a stable, intact self is taken for granted. But, it's a perception that's possible only because of the body image created by the brain. A significant part of that image is a mental map of the body surface generated by the cerebral cortex using the sensory signals it receives from the skin. Other regions of the cortex control other components, such as the position of muscles and joints, the intention to move, and also the visual viewing of the body's movements (New Scientist). Unfortunately, the brain's idea of its body can be distorted by the amputation of a limb. Since there is no visual feedback, initiating motor intention does not activate proprioreceptors (Harris). Over time, phantom limbs can be felt by the amputee to be overflexed, which causes a cramping pain. Based on this information, one of the most common questions is “if the inconsistency between the intention of the brain and the perception of the body's actions was to be resolved, could the phantom pain also be eliminated”? Several theories have been developed over the years that have attempted to answer this question, most notably by Ronald Melzack and Vilayanur Ramachandran.

The earliest hypothesis regarding the cause of phantom limbs and pain was based on the blame of neuromas. These are nodules comprised of remaining nerves located at the end of the stump. According to the theory, neuromas seemingly continued to generate impulses that traveled up the spinal cord to portions of the thalamus and somatosensory domains of the cortex. As a result, treatment involved cutting the nerves just above the neuroma in an attempt to interrupt signaling at each somatosensory level (Journal of Neurology). This and other related theories were not accepted with complete satisfaction because of the fact that the phantom pain always returned, indicating that there was a more complex reason.

Psychologist Ronald Melzack developed the concept of the neuromatrix and the neurosignature. This idea claimed that the brain contained a neuromatrix or a network of neurons that analyzed the sensory information and allowed the perception of feeling (Macalester). Then the neurosignature, which consisted of the three primary neural pathways (from the thalamus to the somatosensory cortex, from the reticular formation of brain stem to limbic system, and the parietal lobes) was activated and informed the brain that the detection of sensation was from itself. He also stated that the neuromatrix, which was essentially a brain map of the body, was pre-wired by genetics. Melzack pointed to his research that showed that people born without a limb could also experience phantom pain (Phantom limbs). He proposed that the brain was predisposed to believe that all of its limbs existed, so it sent out an output signal to the body through the neural pathways in the neuromatrix. Because there was no limb, the brain acquired no sensory feedback. When failed attempts increased the intensity of its signals, the phantom pain was induced. These findings led Melzack to believe that "the body we perceive is in large part built into our brain-it's not entirely learned. In fact, you do not need the body to feel the body” (Phantom limbs).

Other researchers, such as Vilayanur Ramachandran had other answers to the question of phantom pain etiology. He was inspired by previous experiments by Michael Merzenich that had studied the homunculus (blueprint representation of the entire body surface, which identifies the locations of sensations felt on the skin) of monkeys. In these experiments, the sensory nerves in the arms of a group of monkeys were severed. It was found that despite the lack of sensory input from the arm, the arm region of the body map in the cortex hadn't gone silent. Instead, signals from the face (next door on the map) had taken over for the phantom arm (New Scientist). They concluded that there were