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A Pain Called Phantom – Fundamental Science

By Renata Fontanetto

Why do some people feel members that no longer exist?

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“Feet, what do I want them for if I have wings to fly.” The phrase follows a drawing by Frida Kahlo made days before her right leg was amputated. In times of Paralympics, the impressive performance of athletes who lost a limb draws more attention to this type of disability. For many people, the amputation experience can unfold into situations that science is still trying to understand.

Around 80% of the cases in which a limb or organ is removed, either in a planned way or in emergency surgery, the person continues to feel as if it existed. This is called phantom limb sensation: the presence of that part of the body that is gone. Today, it is known that this happens due to physiological changes resulting from the amputation.

The incidence of this feeling is greater when the experience is traumatic, explains Bárbara Pires, a physical education professional and a doctor in medical sciences from the Instituto D’Or de Pesquisa e Ensino, Idor. In addition, the literature is richer in reports referring to limbs, such as arms and legs, about which patients mention itching, tingling, pressure and even movement – ​​voluntary or involuntary. Another manifestation is pain, which is usually chronic and can last for years.

Some scientific hypotheses seek to understand the mechanisms associated with it and why it occurs: the so-called peripheral, central and contextual hypotheses. The peripheral ones try to unravel the phenomenon from the point of view of the corporal periphery. In the amputation stump, some patients develop neuromas, small nodules in the nerve that can trigger pain.

However, according to Pires, today this sensation is better explained by changes that occur at the level of the central nervous system. “Even when the stump regenerates perfectly and there’s nothing in the periphery of the body to justify it, it’s still possible for the person to feel it,” she observes. Therefore, if peripheral hypotheses do not cover everything, the so-called central hypotheses are derived from the brain. After all, a part of the body has been removed, but the brain area that represents it is not. For the researcher, it is important not to discard the third group: contextual hypotheses. Psychological conditions come into play, such as anxiety and depression, which are not described as the cause of pain, but which can affect, for example, the intensity.

If the answer is in the brain, analgesics at the stump site or by other means do not work well. The pain usually returns, and the patient goes back to being medicated with increasingly larger doses. There is no right treatment, but some therapies alleviate symptoms, such as the famous mirror therapy, created by Indian neuroscientist Vilayanur Ramachandran. In it, the patient positions the mirror in such a way in the middle of the body that the mirrored part faces the healthy limb. When performing the movement, the person tricks the brain, as if the leg or the reflected arm were the amputated limb.

In his doctorate, completed in 2020, Pires wondered if he could modulate brain activity in regions related to phantom sensation and pain. In conjunction with the group of specialists at Idor, she conducted a test with upper-limb amputees using a neuroimaging technique: functional magnetic resonance neurofeedback. Secondarily, it analyzed whether modulation of brain activity affected pain.

If it is possible that the sensation occurs because there is some alteration in the brain representations of the removed limb, then it is worth observing the brain live. One of the researcher’s requests to the study participants was precisely that they move the phantom limb inside the resonance device. Meanwhile, a team was checking brain activity. The work had the guidance of scientists Fernanda Tovar-Moll and Erika Rodrigues, in addition to having been carried out with the National Institute of Traumatology and Orthopedics, Into, a reference in the Unified Health System.

“From a better understanding of the physiological mechanisms behind these phenomena, we can validate or reinforce hypotheses and perhaps develop more effective treatments in the future,” says Pires. The thesis article is in the submission phase, undergoing evaluation, and soon new perspectives will help to build scientific knowledge about these ghosts.

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Renata Fontanetto is a journalist and a master in science communication from Fiocruz.

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