Advanced bionic limbs mapped in the brain for the first time.

Neuroprosthesis research in amputee patients aims to develop new prostheses which move and feel like real limbs. Targeted muscle and sensory reinnervation (TMSR) enables amputees to control robotic prosthetic devices using their brain and to regain sensory feedback.  TMSR changes the way the brain processes motor control and somatosensory input; however these detailed brain mechanisms have never been mapped before.  Now, a study from researchers led by EPFL identifies 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 team state that the success of TMSR prostheses will depend on the ability to understand the ways the brain re-maps these pathways. The opensource study is published in the journal Brain.

Previous studies show that a patient fitted with a TMSR prosthetic sends motor commands to re-innervated muscles, where movement intentions are decoded and sent to the prosthetic limb. Direct stimulation of the skin over the re-innervated muscles is then sent back to the brain, inducing touch perception on the missing limb.  However, it is not clearly demonstrated to what extent TMSR-based prostheses recruit and reinstate cortical representations of the missing limb.  The current study maps changes in the cortices of three patients with upper-limb amputations who have undergone TMSR.

The current study utilises fMRI to show how a bionic prosthesis for upper limb amputees based on TMSR impacts the functional organization of the missing limb in the cortices.  Results show that motor cortex maps of the amputated limb were similar in terms of extent, strength, and topography to individuals without limb amputation.  Data findings show that motor cortex maps were different from patients with amputations who were using standard prostheses which shows the unique impact of the surgical TMSR procedure on the brain’s motor map.

Result show the connections between upper-limb maps in both cortices are normal in the TMSR patients, which were comparable with healthy controls.  Data findings show that preservation of original mapping was reduced in non-TMSR patients, showing that the TMSR procedure preserves strong functional connections between primary sensory and motor cortex.  The lab explains that despite enabling good motor performance, TMSR-empowered artificial limbs still do not move and feel like a real limb and are still not encoded by the patient’s brain as a real limb. The group conclude that future TMSR prosthetics should implement systematic somatosensory feedback linked to the robotic hand movements, enabling patients to feel the sensory consequences of the movements of their artificial limb.

The team surmise their findings provide the first detailed neuroimaging investigation in patients with bionic limbs based on the TMSR prosthesis, and show that fMRI is an exceptional tool for studying the upper-limb maps of the motor and somatosensory cortex following amputation.  For the future, the researchers state that there is a need for further engineering advances such as the integration of somatosensory feedback into current prosthetics which can enable them to move and feel like real limbs.

Source: EPFL Biomedical Imaging Research Center


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