Surprisingly, the study showed that motor cortex maps of the amputated limb were similar in terms of extent, strength, and topography to individuals without limb amputation, but they were different from patients with amputations that did not receive TMSR, but were using standard prostheses. This shows the unique impact of the surgical TMSR procedure on the brain's motor map.

The approach was even able to identify maps of missing (phantom) fingers in the somatosensory cortex of the TMSR patients that were activated through the reinnervated skin regions from the chest or residual limb.


The somatosensory maps showed that the brain had preserved its original topographical organization, although to a lesser degree than in healthy subjects. Moreover, when investigating the connections between upper-limb maps in both cortices, the researchers found normal connections in the TMSR patients, which were comparable with healthy controls. However, preservation of original mapping was again reduced in non-TMSR patients, showing that the TMSR procedure preserves strong functional connections between primary sensory and motor cortex.

The study also showed that TMSR is still in need of improvement: the connections between the primary sensory and motor cortex with the higher-level embodiment regions in fronto-parietal cortex were as weak in the TMSR patients as in the non-TMSR patients, and differed with respect to healthy subjects.

This suggests 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 scientists 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 findings provide the first detailed neuroimaging investigation in patients with bionic limbs based on the TMSR prosthesis, and show that ultra-high field 7 Tesla fMRI is an exceptional tool for studying the upper-limb maps of the motor and somatosensory cortex following amputation.

In addition, the findings suggest that TMSR may counteract poorly adapted plasticity in the cortex after losing a limb. According to the authors, this may provide new insights into the nature and the reversibility of cortical plasticity in patients with amputations and its link to phantom limb syndrome and pain.

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