Brain-mapping study could help make bionic limbs feel more lifelike
The brains of people with bionic limbs have been mapped in never-seen-before detail in a move that could revolutionise the future of prosthetics.
Targeted motor and sensory reinnervation (TMSR) is used on amputation patients so that they can gain some control of a prosthetic limb, along with sensory feedback. This involves connecting residual nerves from the missing limb to intact muscle and skin.
TMSR completely changes the way the brain processes motor and touch input, remapping motor and sensory pathways to accommodate the new bionic limb. Until now, these brain mechanisms had not been fully investigated.
In the new study, an international team of researchers including the University Hospital of Lausanne, used ultra-high field 7 Tesla fMRI scanning to map out these changes in the brains of three patients with upper limb amputations, who had were prosthetic limb users and who had also undergone TMSR. The study concentrated on the primary motor and somatosensory cortex, the part of the brain that deals with movement and sensory inputs from the body, such as touch, pain and pressure. The scanning technique used measures brain activity by detecting changes in blood flow across it.
Surprisingly, the study showed that motor cortex maps of the amputated limb were similar to individuals without limb amputation. However, they were different from patients with amputations who had standard prostheses and had not received TMSR. This shows the huge impact that TMSR has on the brain’s motor mapping and its ability to help bionic limbs mimic the real thing.
The future of lifelike prosthetics relies on understanding on the brain re-maps inputs from the new bionic limb, which is why the study is so important. A better understanding of the brain’s ability to organise itself with new neural connections based on its environment and individual experiences could also give scientists a better understanding of phantom limb syndrome, where phantom sensations are experienced after a part of the body is removed.
However, the research also shows that TMSR is still in need of improvement as the connections between the primary sensory and motor cortex were just as weak in the TMSR patients as the in the non-TMSR patients, but differed compared to the non-amputees.
“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,” say the researchers.
The team concludes that future TMSR prosthetics should feature touch-based feedback linked to the robotic hand movements so that patients can feel the sensory consequences of the movements of their artificial limb.
The research is published in the journal Brain.
Image credit: Irit Hacmun, Tel Aviv