Introduced by American physician Silas Weir Mitchell in 1872, the term “phantom limb” is used to describe the sensation that an amputated limb is still attached to the body. Nearly all amputees report having a phantom limb experience, and for the majority, it is excruciatingly painful. In fact, according to neurologist Vilayanur S. Ramachandran at the Center for the Brain and Cognition at the University of California, San Diego, nearly 70 percent of amputees continue to suffer from intermittent pain in a limb decades after it has been removed. Phantom limb pain can have a debilitating and devastating effect on a patient’s life. Unfortunately, most current treatments are ineffective because the biological basis for the pain is not completely understood.
Exploring the Biological Cause of Phantom Limb Pain
In the Scientific American article “Living with Ghostly Limbs,” Miguel Nicolelis, M.D., Ph.D., a Brazilian professor of neurology and biology at Duke University Medical Center explores the biological cause of and innovative treatments for phantom limb pain. According to Nicolelis, most scientists believe that phantom limb perceptions stem from residual activity in the regions of the neuromatrix formerly assigned to the missing limb. In addition, he suggests that future phantom limb treatments may include brain remapping techniques.
Nicolelis cites the results of several experiments performed on the peripheral nervous system to support the theory that a complex neuromatrix develops and controls our body image, including:
- Amputees with a severed peripheral nervous system continued to suffer from phantom limb pain, which suggests the source is more likely the brain;
- When different, but specific, areas of the brain are damaged, a drastic change in body image and perception occurs, which indicates that they are result of a complex, interactive network in the brain, rather than just the function of one localized region;
- When a person experiences a drastic change in body structure, corresponding changes can be observed in the brain, which supports the theories of neural plasticity and brain remapping.
Understanding the Body Image Neuromatrix
According to Ronald Melzack, Ph.D., of McGill University the body image neuromatrix is composed of four major parts: the somatosensory cortex, regions of the parietal lobe and two neural pathways. Additional research by Ramachandran indicates the likelihood of phantom limb pain is significantly reduced in young children, suggesting that the body image neuromatrix is formed during the first our first eight years of development.
In the past, scientists believed that once the neuromatrix was fully developed, it could not be reconfigured. As a result, treatments ranging from prescription drugs and acupuncture to electric spinal cord stimulation (SCS) were used to treat phantom limb pain – all with marginal success. Based upon experiments that show sensory input activates nearby areas of the Penfield map of the motor cortex after a limb is amputated, scientists now believe that the brain is more flexible, and therefore, the neuromatrix can be reorganized.
Treatment for Phantom Limb Pain
This research and insight into the organizational structure of the brain creates a huge opportunity for a new and exciting treatment for phantom limb pain – illusions. For example, Ramachandran and his colleagues are using mirrors to create the illusion that the phantom limb is real. Their belief is that altering the body image perception triggers remapping in the brain, which dissolved the “pain memories.” Taking this concept one step further, other researchers are beginning to use virtual reality tools to simulate phantom limbs, with the hope of improving the results experienced by Ramachandran.
Because severity of pain before amputation is a major risk factor, the best treatment for phantom limb pain begins before the phenomenon starts. Before surgery, patients should be as pain-free as possible. In addition, special care should be taken to ensure the patient heals quickly and without complications. Finally, if phantom limb pain develops, it may be most effectively treated by reorganizing the brain. While this may currently require the use of rudimentary illusion methods like the mirror box, there is no doubt that a better understanding of the neuromatrix and advancements in technology may enable future treatments like stimulation of specified brain regions and enhanced methods of creating illusions, perhaps by integrating the use of holograms, lasers and things perhaps we can only dream of at this point in time.
Implications for Future Treatment of Phantom Limb Pain
These advancements in treatment of phantom limb pain also have larger implications for science and medicine. The more we understand about the organizational function of the brain, the more effective we will be at treating any disorder, including pain. Eventually, we may also be able to recreate the “system” leading to advancements in limb replacement, robotics and artificial intelligence.