Researchers at the Ecole Polytechnique Fédérale de Lausanne in Switzerland have developed a new technique to help amputees use their prostheses. The method involves virtual reality and neural stimulation to help change an amputee’s “phantom limb” to more closely match their prosthetic limb, making it easier and more natural to use.

Amputees frequently experience sensations from their missing limbs. Typically, such “phantom limbs” are perceived as much smaller than the original limb. Commercially available prosthetic limbs do not typically offer experiences of sensation and touch, and they also match the size of the original limb, leading to a discrepancy between what an amputee experiences (i.e. their small phantom limb) and the reality of using a prosthetic limb. This might make someone feel clumsy or uncomfortable, and can limit how often amputees use their prostheses.

To address this issue, the Swiss researchers set out to change an amputee’s perception of their prosthetic, so that it feels more like their own limb. “The brain regularly uses its senses to evaluate what belongs to the body and what is external to the body. We showed exactly how vision and touch can be combined to trick the amputee’s brain into feeling what it sees, inducing embodiment of the prosthetic hand with an additional effect that the phantom limb grows into the prosthetic one,” said Giulio Rognini, a researcher involved in the study. “The setup is portable and could one day be turned into a therapy to help patients embody their prosthetic limb permanently.”

The technique involves amputees wearing a virtual reality headset through which they can view a virtual prosthetic limb. By applying a stimulus to a nerve in the amputee’s stump, the researchers could create the illusion that a digit in their phantom limb (in this case the index finger) was experiencing a sensation. Simultaneously, the index finger in the virtual prosthetic glowed, helping to create the illusion that the phantom limb and the prosthetic are one and the same.

The simulation resulted in users feeling that their phantom limb grew to become the larger prosthetic. As the effect lasted for about 10 minutes after completing the simulation, the researchers hope that it could provide a longer term or even permanent treatment in the future. They also wish to examine if the simulation can have therapeutic effects on the phantom pain experienced by amputees.