A pain called a phantom – basic science

By Renata Fontanetto

Why do some people feel members who no longer exist?

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“Feet, what do I want them for when I have wings to fly.” The sentence follows a drawing by Frida Kahlo made days before the amputation of her right leg. During the Paralympic Games, the impressive achievements of athletes who have lost a limb draw more attention to this type of disability. For many people, the amputation experience can unfold in situations that science is still trying to understand.

About 80% of the times when a limb or organ is removed, scheduled or in emergency surgery, the person continues to feel like it is there. This is known as the phantom sensation of the limb: the presence of the part of the body that has disappeared. Today we know that this happens through physiological changes as a result of the amputation.

This feeling is more common when the experience is traumatic, explains Bárbara Pires, physical education teacher and doctor of medical sciences at Instituto D’Or de Pesquisa e Ensino, Idor. In addition, the literature is richer in accounts of limbs such as arms and legs that patients mention itching, tingling, pressure, and even movement – voluntarily or involuntarily. Another manifestation is pain, which is mostly chronic and can last for years.

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

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

If the answer is in the brain, then analgesics at the stump site or otherwise won’t work well. The pain usually returns and the patient continues to receive medication in increasing doses. There is no right treatment, but some therapies relieve symptoms, such as the famous mirror therapy developed by Indian neuroscientist Vilayanur Ramachandran. The patient positions the mirror in the middle of the body so that the mirrored part faces the healthy extremity. In performing the movement, the person fools the brain as if the leg or reflected arm were the amputated limb.

In his doctoral thesis, completed in 2020, Pires wondered if he could modulate brain activity in regions associated with phantom sensation and pain. In collaboration with the group of specialists from Idor, she carried out a test with upper arm amputees using a neuroimaging technique: functional magnetic resonance neurofeedback. Second, it was analyzed whether the modulation of brain activity affects pain.

If it is possible that the sensation occurs because the brain representations of the distant extremity are altered, it is worth observing the brain live. One of the demands the researchers made on the study participants was precisely that they move the phantom limb in the resonance device. Meanwhile, a team checked the brain activity. The work was led by scientists Fernanda Tovar-Moll and Erika Rodrigues and was carried out with the National Institute of Traumatology and Orthopedics Into, a reference in the Unified Health System.

“By better understanding the physiological mechanisms behind these phenomena, we can validate or reinforce hypotheses and perhaps develop more effective treatments in the future,” says Pires. The dissertation article will be submitted, evaluated and soon new perspectives will contribute to building up scientific knowledge about these spirits.

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Renata Fontanetto is a journalist and Masters in Science Communication from Fiocruz.

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