Ten amputees and phantom pain patients saw their suffering subside thanks to innovative training using a robotic arm.
The sensation is comparable to that of a burning or hypersensitivity. But no limb is attached to this discomfort. This is called phantom pain. Among amputees, 50 to 80% suffer from it. The brain mechanism at work was uncovered by two teams, from the universities of Osaka (Japan) and Cambridge (United Kingdom). They publish their findings in Nature Communications and outline a treatment path for this pain.
Act on the opposite arm
The study relies on a brain-machine interface, which decodes neuronal activity to move a prosthetic hand. For this the user must remember to move his missing hand. But the researchers found that this approach was counterproductive in the 10 patients included in the protocol. “The more their amputated arm responded well to the use of the robotic arm, the more they suffered,” explains Takufumi Yanagisawa, first author of the study. The motor area of the brain is functioning properly, but it is not getting sensory feedback, there is a lag. “
The technique was therefore modified according to these parameters. Volunteers were asked to replicate the experiment. But this time, they had to associate the movement with the hand still in place. For example, if the left arm is missing, the participant should practice moving the prosthetic arm by imagining moving the right arm. A counter-intuitive but effective approach: the patients suffered less.
Plasticity of the brain
This phenomenon is explained by the impact of amputation on the brain. The mechanisms associated with sensation and movement are disrupted. By rearranging this, the pain recedes. The technique also has the advantage of taking advantage of the plasticity of the brain. Until now, specialists believed that phantom pain was related to a poor connection in the sensorimotor cortex, the area responsible for sensory input and the execution of movement.
The scope of this work is potentially very broad. Researchers are considering an application in other pathologies that induce chronic pain, such as arthritis. However, it will be necessary to be patient: the team does not envisage generalized use for 5 or 10 years.
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