Targeted motor and sensory reinnervation (TMSR) is a surgical procedure on patients with amputations that reroutes residual limb nerves towards intact muscles and skin in order to fit them with a limb prosthesis allowing unprecedented control. By its nature, TMSR changes the way the brain processes motor control and somatosensory input; however the detailed brain mechanisms have never been investigated before and the success of TMSR prostheses will depend on our ability to understand the ways the brain re-maps these pathways. Now, EPFL scientists have used ultra-high field 7 Tesla fMRI to show how TMSR affects upper-limb representations in the brains of patients with amputations, in particular in primary motor cortex and the somatosensory cortex and regions processing more complex brain functions. The findings are published in Brain.

Targeted muscle and sensory reinnervation (TMSR) is used to improve the control of upper limb prostheses. Residual nerves from the amputated limb are transferred to reinnervate and activate new muscle targets. This way, a patient fitted with a TMSR prosthetic "sends" motor commands to the re-innervated muscles, where his or her movement intentions are decoded and sent to the prosthetic limb. On the other hand, direct stimulation of the skin over the re-innervated muscles is sent back to the brain, inducing touch perception on the missing limb.

But how does the brain encode and integrate such artificial touch and movements of the prosthetic limb? How does this impact our ability to better integrate and control prosthetics? Achieving and fine-tuning such control depends on knowing how the patient's brain re-maps various motor and somatosensory pathways in the motor cortex and the somatosensory cortex.
The lab of Olaf Blanke at EPFL, in collaboration with Andrea Serino at the University Hospital of Lausanne and teams of clinicians and researchers in Switzerland and abroad have successfully mapped out these changes in the cortices of three patients with upper-limb amputations who had undergone TMSR and were proficient users of prosthetic limbs developed by Todd Kuiken and his group at the Rehabilitation Institute of Chicago.

The scientists used ultra-high field 7T functional magnetic resonance imaging (fMRI), a technique that measures brain activity by detecting changes in blood flow across it. This gave them an unprecedented insight at great spatial resolution into the cortical organization of primary motor and somatosensory cortex of each patient.

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