18/05/2026
The participant was blindfolded. As the Experiment 2 started, he was sitting comfortably and recalled all instructions.
“An evaluation will be made with a cotton swab. I will touch some regions of your body and you must tell me what you are feeling”.
Soon enough he touched his chest with the left hand to indicate he felt something there.
He thought: “how does the sensation feels like?” Recalling the instructions, a few examples came to his mind.
“pressure, vibration, pricking, burning, squeezing, touch, itch, cold…”
- Yes. - he said according to the instructions, indicating he felt something.
- Where?
- Right here. Something pricking my chest.
- Ok! Let me mark it with the pencil…good, there you go. Now, let’s move on.
This was 833 days after surgery, the injured arm resting on a pillow, the other pointing whenever he felt something.
In total, 81 points where stimulated, of which 48 evoked correctly placed sensations and 27 evoked the so-called RS.
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Referred sensation (RS) is described as “the sensation evoked in the skin areas other than the stimulated region”. It is common in people after severe peripheral injury and there are a few possible explanations.
Some people with the Brachial Plexus Injury (BPI) have also reported experiences of RS. This set of nerves communicates with the brain information from our arms: sensations, movements, postures, etc. It helps us identify objects, perceive temperatures and pain, coordinate motor control and so on.
The mission of NeuroMat’s initiative ABRAÇO is to welcome and guide patients who have suffered BPI, so as families and health professionals. Thanks to ABRAÇO network, this cooperation also made viable studies to improve our comprehension of BPI-related issues such as this one.
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Schmaedeke and colleagues’ preprint (2024; see Ref. 1) report two experiments designed to mapping RS in Traumatic Brachial Plexus Injury patients. The fictional scene that introduced our post was inspired by real data and passages from the paper.
In the first experiment, 12 participants underwent a referred sensation screening. The procedure consists of skin stimulation in areas distributed across upper limbs, neck, and face. The second one was performed with the Semmes-Weinstein monofilament technique in 3 patients that have reported RS before (two of them during Experiment 1). “The protocol was adapted from that used in amputees to map the sensation of the amputated limb after surgical targeted sensory reinnervation”, the authors detail (p. 4).
Importantly, all subjects had a motorcycle accident that led to complete left BPI. Hence, part of the effort of ABRAÇO is to disseminate knowledge about this correlation, since more than 80% of the injuries are due to motorcycle accidents.
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This was the first study to map systematically the RS in patients with Traumatic Brachial Plexus Injury. A possible explanation for the phenomenon involves how cortical sensorimotor regions reorganize themselves after the surgery, where specific nerves are transferred to replace those damaged in the affected area, perhaps allowing patients to retrieve some of the functions in the area.
The large amount of sensory fibers present in the donor nerve my undergo reinnervation, resulting in a sort of cross-communication. Also, “after nerve repair, nerve fibers can also grow misdirected, achieving the wrong, non-intended skin regions”.
One of the patients was assessed three times over 6.3 years. Notably, “it is possible to see a scattering of RS over the course of time”. Although the study states its limitations regarding the small sample of patients, these insights collaborate to expanding our understanding on referred sensation and possible explanations to the phenomenon.
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Learn more about ABRAÇO in our website: https://abraco.numec.prp.usp.br .
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Blindfolded | The “Black Box of Science” series
References:
1. Schmaedeke, A. C.; Erthal, F. S.; Vargas, C. D.; Ramalho, B. L. Mapping Referred Sensation in Traumatic Brachial Plexus Injury Patients. meRxiv preprint. DOI: https://doi.org/10.1101/2024.02.19.23297564
Página inicial | ABRAÇO A missão da iniciativa ABRAÇO é acolher e orientar pacientes que sofreram uma lesão traumática do plexo braquial e seus familiares, oferecer treinamento e capacitação para profissionais interessados e divulgar pesquisa em desenvolvimento sobre a lesão e suas consequências funcionais.
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