Scientists at the Swiss Federal Institute of Technology of Lausanne (EPFL) working with investigators in other institutions, managed to see, using functional magnetic resonance imaging (fMRI), how the brain reorganizes itself after a person is treated with targeted motor and sensory reinnervation (TMSR). TMSR is a method of redirecting existing nerves on or near the amputee’s stump to muscles and skin areas. Sensors can then detect that a nerve activates a muscle, for example, and use that to control a prosthetic device. The result is an easy and intuitive way for amputees to manipulate advanced prostheses that have multiple degrees of freedom of movement.

An amputee fitted with an advanced arm prosthetic following TMSR surgery (credit: Irit Hacmun, Tel Aviv)

The brain has to re-map the neural pathways in order to associate the generation of particular signals in the brain to the movement of a prosthesis. These pathways are different from the ones evolution established, but because of neuroplasticity, the brain is able to adapt and let other parts of itself control limbs that those brain regions were never designed to control. The same principle applies to sensory reinnervation that helps to relay a sense of touch from a prosthesis to the brain.

To image the brain with the necessary resolution, the EPFL scientists used a high-field 7 Tesla MRI machine to compare patients that have undergone TMSR versus those that use more traditional powered prostheses. The investigators discovered that in the TMSR patients, the brain remapped the region associated with movement of the affected limb to another part of the brain, and that the remapping retained a similar size and shape as in healthy subjects. But, the people that used traditional prostheses did not exhibit a similar remapping, demonstrating the fundamental benefit of TMSR.

The new knowledge should help in improving TMSR and getting the brain acquainted faster at using new prostheses.