Sensation and Perception: Phantom Limb Pain - Essay Example

? Sensation and perception: What can phantom limb pain teach us about the human brain? due: Introduction A phantom limb is the impression that a surgically removed or missing limb is connected to the body and coordinates with the other body organs. This sensation is experienced by approximately 60-80% of all amputees with the majority experiencing phantom pain. Other than limbs, phantom pains and other sensations also occur for other amputated parts of the body. These may include the eyes, breasts, teeth etc. The amputees have reported the missing limbs to feel shorter than normal and out of place or distorted. Phantom limb pains can be intensified by anxiety, stress and weather changes. The pains are normally intermittent, and the intensity of their occurrence usually decreases with time (Mather, & Mather, 2009). While experiencing the phantom limb pains, patients also report sensations of gesturing, itching and twitching, plus they even try to pick objects up. The pain itself is described as a burning sensation, but its exact nature varies with individuals. Other common sensations include variations in temperature, tingling, shock, stabbing sensations and perceived motions of the missing limbs. The limb may also feel as if it is retracting into the stump, an occurrence known as telescoping. The phantom may also elicit some sensations when the retained stump if touched (Ward, 2008). What can phantom limb pain teach us about the human brain? It was previously thought that phantom limb pain was caused by irritation in the severed nerve endings on the amputated limbs. When a limb is amputated, the nerves terminate and inflame at the point of amputation. The nerve endings were thought relay analogous signals to the rain, which were then interpreted as pain. Surgeons then developed treatments based on this theory, but they all failed. In one, case, the surgeons would further shorten the amputated limb in an attempt to remove the inflamed nerve endings and bring temporary relief to the patients. This however, resulted in increased pain and the patients were left with the sensations of both the original limb and the amputated stump. In other extreme cases, surgeons cut the sensory nerves that leads to the spinal cord or completely removes the section of the thalamus which receives sensory information from the body (Ramachadran & Blackese, 1999). In the early 1980s, scientists concluded that the inflamed nerve endings theory was incorrect. Later on, Vilayanur S. Ramachandran came up with the theory that phantom limb pains, together with all other phantom limb sensations, resulted from the reorganization of the somatosensory cortex. The somatosensory cortex receives sensory information from the body and is located in the post central gyrus. This reorganization, he explains, occurs when the sensory input, in this case being the limb, is lost (amputated). He further went on to demonstrate this theory by stroking various parts of the face to show how this led perceptions being felt on different parts of the missing limb. The perceived sensing of being touched in the phantom limb as a result of being touched on the face was according to Ramachandran, the perceptual correlate of the cortical reorganization. Other scientists, however, disputed these findings claiming that the sensations in the phantom limbs are correlated with a wide network of neural activity outside the cortex (Ramachadran & Blackese, 1999). Later on, a scientist known as Tim Pons, who worked at the National Institutes of Health, illustrated the brain's ability to recognize that a sensory input has been cut off. Ramachandran added on Pons’ research with the theory that the phantom sensations could be due to cross wiring in the somatosensory cortex. The input from extreme occurrences comes into the somatosensory organ in an organized way, where input from the foot is located next to that from the hand while input from the hand is located next to that of the face. Ramachandran concluded that following a loss of the right hand in an accident, a person would have feelings of a phantom appendage because the input that normally goes from hand to the left somatosensory has been stopped and vice versa. In later research, scientists experimented on the subject, where they used visual imagery to contort the phantom limbs of seven arm amputees. Out of the seven, four succeeded in twisting their phantom arms into impossible positions. This result implied that the amputees had managed to modify the neural representation of their phantom arms. They were able to generate the motor commands needed to twist them into impossible positions; with the absence of feedback from the body. This finding illustrated the plasticity or flexibility of the brain because it showed that considerable changes in the body can be induced by brain mechanisms (Murray, 2009). Another recent experiment was performed by Ramachandran, where the subject was a woman who was born with a deformed right hand consisting of three fingers only and a rudimentary thumb. She had earlier gotten involved in a car crash, and her hand was amputated which resulted to sensations of a phantom hand. The phantom hand, however, felt to have all five fingers, although some were perceived to be shorter than normal. The woman also began to experience severe phantom limb pain and sought treatment. Ramachandran then experimented on the woman using visual imagery to contort the phantom hand. In the reflection, her healthy hand appeared where it was supposed to be, and in two, weeks the woman was able to move her now then fully formed phantom fingers plus she was also relieved of the pain. The scientist then stated this to be proof that the brain possesses an innate template of a hand that is fully formed. These and various other experiments carried out by scientists lead to the conclusions that; various patients experience varying degrees and types of pain. The phantom limbs are perceived as well as the ability to carry out various functions with them; touching the face can produce some projections of sensation into the phantom limb, severe pain in the phantom limb can extend to other body parts, and various distractions in the patient’s personal life can help to control the phantom limb pain (Ward, 2008). The phantom limb phenomenon has also been reported on some patients with spinal cord damage, but no amputation. This shows that the phantom limb phenomenon may also be as a result of damage to pathways involved in pain sensation (Nelson, 2013). Up to now, the exact mechanisms behind phantom limb pain are not clearly known. It is however, indisputable that the phenomenon, together with other sensations, is closely linked to brain plasticity and reorganization as seen in the above experiments. The human brain has an astounding capability to change its connections and functioning; in response to daily learning the changes in the environment, like the setting of an injury. Reorganization may occur in selected nerves in the amputated limbs, the cerebral cortex, the spinal cord or some sections of the brain like the cerebral cortex and the thalamus (Melzack, 1983). Conclusion Research on phantom limbs and their neural causes has highly advanced over the last decade. This phenomenon has provided an important opportunity for the understanding of the human brain and how it continually adjusts its perception of reality in response to the various sensory inputs. Phantom sensations provide proof of an ever changing cortical mapping of the human brain. Apart from their importance to neural plasticity and body image, the research on phantom limbs also enlightens us on the relationship between neuron activity and consciousness. In phantom limb patients, one can clearly track the progressive changes in neural mapping with time as seen with the experiment involving the woman with an amputated arm. In time, this experience may enable us to determine how the workings of these maps influence the development of phantom perceptions. Indeed, such experiments provide a bridge into the understanding of some of the theories in physiology, like the Muller’s law of nerve energies. For example, some upper limb amputees usually experience dual sensations. When the face is touched, for example, the subject feels the touch both on the face and the phantom hand. The most probable explanation to this is that the two points get simultaneously activated at the same sensory point in the brain. This observation explains that there occurs an initial overshoot during remapping such that the input from the hand skin to the cortical face sensory region is stronger than the input to the hand area; thus it dominates the perception and masks the sensation on the hand. References Mather, G., & Mather, G. (2009). Foundations of sensation and perception. Hove, East Sussex [England: Psychology Press. Melzack, R. (1983). Pain measurement and assessment. New York: Raven Press. Murray, C. D. (2009). Amputation, prosthesis use, and phantom limb pain: An interdisciplinary perspective. New York: Springer. Nelson, D. (2013). The mystery of pain. Ramachadran, V., and Blackese, S. (1999). Phantoms in the Brain: Human Nature and the Architecture of the Mind. London: Harper Collins Fourth Estate. Ward, J. (2008). The Frog who Croaked Blue: Synaesthesia and the Mixing of the Senses. Abingdon: Routledge. Read More