Neuroplasticity, Sensory Remapping, and Phantom Limb Pain
In the 1950s, Canadian neurosurgeon Wilder Penfield demonstrated areas of the brain that map bodily sensation and perception in the parietal lobes. A schematic model of these sensory representations became known as the Penfield Homunculus.
In 1986, Wain tested the efficacy of hypnosis in treating phantom limb pain. One pertinent finding was that effective hypnosis can help patients regain a sense of control over their difficulties.
In 1990, researchers Arena, Sherman, Bruno, and Smith demonstrated a significant relationship between stress and limb pain, with each affecting the other in a recursive relationship. One recommendation was the use of psychophysiological interventions to interrupt this cycle.
In his groundbreaking book Phantoms in the Brain, V. S. Ramachandran describes how the brain can “remap” a missing limb onto sensory areas adjacent to the sensory cortex in the parietal lobe. For example, he reports cases in which a phantom hand is remapped onto the corresponding cheek – such that sensations felt on the cheek are also felt in the phantom hand.
These remapped sensations can be sensory-specific, meaning that a drop of water on the cheek is experienced like a drop of water on the hand. Hot and cold sensations may also be experienced in corresponding ways.
The remapping can be precise enough that the felt sensation of specific regions of the phantom hand can be mapped and drawn onto corresponding regions of the cheek.
Other forms of remapping are reported. For example, because the genitals and feet are adjacent in the sensory cortex, it is sometimes reported that lower-leg amputees experience orgasmic sensations in a phantom foot. In such cases, orgasm may be experienced as more intense, potentially because it is represented over a larger cortical area.
Virtually any amputated body part can be experienced as a phantom. Reports include phantom breasts, noses, and penises.
Other possible influences on phantom pain include inflamed neuromas in the stump region and/or scar tissue in the stump.
The term ‘neuroplasticity’ describes the brain’s capacity to reorganise and remap its functions. For example, in individuals who learn sign language following profound hearing loss, visual systems can assume functions typically associated with auditory language processing. Research into the speed with which phantom limb pain can emerge suggests neuroplasticity is more rapid and extensive than was previously believed.