Biology 202
2003 Second Web Paper
On Serendip

Do amputee patients actually feel pain in missing limbs? If so how and why? These are some of the questions that have been asked for many years. One particular case study example displays this phenomenon. In 1983 a man named Aryee lost his right arm in an accident during a storm at sea. An experiment was done on him with the following results related in this dialogue between patient and observer:
'-"See if you can reach out and grab this cup in your right hand. What are you feeling now?
-I feel my fingers clasping the cup.
-Okay try it again." (As the patient tries to reach for the cup, the doctor pulls it farther away)
-Ouch! Why did you do that?
-Do what?
-It felt like you ripped the cup right out of my fingers"' (2) .
This dialogue that occurred between Aryee and the experimenter is a description of a common sensation felt by many amputee patients. Although they are missing an arm, finger, or leg, they have sensations similar to Aryee that include tingles, itching, and even pain where the limb used to be. Thus these patients feel sensations "which seem to emanate from the amputated part of the limb" (4). Phantom limb is the name for this type of phenomenon.

Phantom limb is not a newly discovered occurrence among amputee victims; however it has persisted as a medical mystery for hundreds of years. Even the words associated with the sensation phantom and phenomena suggest that it is somehow out of the ordinary and without a rational explanation. Nonetheless, there is a long documented history of phantom limbs. During the Civil War, in 1872, Silas Weir Mitchell who worked at a hospital in Philadelphia wrote the first clinical documents on patients that experienced feeling where their missing limb used to be located (2) , (5). Today amputees are still experiencing this phenomenon. The sensation of phantom limbs "occurs in 95-100 percent of amputees who lose an arm or leg" (6). At first people merely feel sensations coming from their amputated limb, however in time it develops into pains of stabbing, burning, or cramping (4). In addition, temperature and texture can be felt, such as warmth, cold, and rough surfaces (6). While the phantom limb now a day is no longer considered a myth, rather a legitimatized medically proved sensation the source of these sensations is still a topic of much debate. There are many theories neurobiologists argue are the cause of phantom limb. Two of these theories are based on two differing concepts of the brain: one that the brain is hardwired, the other that the brain, particularly, the cortex can be reorganized.

There was a time when the belief was held in the scientific community that adult brains lost their plasticity after adolescence (3). The idea was that there was no ability for change in the cortex but that the brain is considered to be hardwired with particularly functions that continue despite the fact that a limb might be missing. Michael Merzenich supported this theory with research on monkeys. He amputated the index finger of an adult monkey and recorded the signals that reached the cortical map (2). In the somatosensory cortex there is the representation of the human body called the homunculus, which is like a map of the body (2). The experiment resulted in the discovery that neurons in the index finger region of the homunculus were fired whenever fingers next to the amputated one were touched (2). In this experiment there was no evidence for neuronal growth, rather "unmasking [which] sends new impulses to the previously empty region" (2). Existing axon branches uncover at some point after the amputation and continue to operate. This concept is linked to the fact that body image or perception of the body is genetically hardwired in the brain (1), thus the cause of phantom limbs.

The other theory about the causation of phantom limbs is based on a discovery by T.P. Pons. In his experiment on Silver Spring Monkeys, he discovered that the face region of the cortex replaced the amputated arm's cortex. Thus there is a reorganization of the brain, in which axonal branches sprouted up from facial cortex across amputated limbs area (2). Sensations in the phantom limb can simultaneously be felt in the face. This may mean that the actual physical sensations the patients are experiencing are being processed by the face, but associated with the missing limb. "The brain has reorganized itself after the brain the injury [amputation] such that neurons that were responsive to the missing inputs become responsive to remaining inputs" (3). For Pons and then other neurobiologists that followed this line of thought, the brain could not be hardwired. Instead this experiment suggests that if the cortex can change and alter in such a way it can't possible be as set in stone as once thought.

Phantom limbs are an intriguing concept. The thought that our body can feel what is not there has been a much debated and analyzed part of the human nervous system. Although many theories have been experimented and debated, the idea that seems most probable is that the brain reorganizes itself to deal with the change of the body. In all that the brain can do and does do it seems impossible for something like phantom limbs to happen in a brain that is hardwired, rather the possibility that with the change in the body the brain changes as well seems highly likely. The only question that remains, which may require further research, is why the face region of the cortex takes over the amputated limb region as opposed to other regions?

References

2)Biology Homepage for Macalester, discussion of phantom limbs.

3)College Biology Page, information on reorganization of cortex.

4)Harvard Biology page, article on phantom limbs.

5) Ramachandran, Vilayanur. "Phantom Limbs and Neural Plasticity." Neurological Review March 2000: 317-320

6)MIT Phantom Limb Page.


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