One-handed people who use a prosthesis regularly are more likely to be brain-wired ‘to visualize’ their artificial limb as a part of their body, a new study shows.
Co-authored by Western neuroscientist Jody Culham of the Brain and Mind Institute, the study suggests visual pathways in the brain can repurpose themselves and help coax motor pathways to use a prosthetic limb more often and more effectively.
“A lot of people resist (using) a prosthesis. Our research shows if they do adopt a prosthesis, their brain wires up differently,” said Culham, also professor in the Department of Psychology and Graduate Program in Neuroscience.
Recently published in the journal Brain, the paper – Artificial limb representation in amputees – shows that the more one-handed people use their limb, the more likely their brain is to recognize it as part of their body. That sensation is regardless of what the artificial limb actually looks like – just as it would recognize their other hand.
The study was unclear whether more frequent use prompts brain recognition, or whether brain recognition motivates people to use the limb more often and more functionally, Culham said.
The research could be helpful in shaping how rehabilitation takes place after amputation. It could also be used to help design better, more user-friendly artificial limbs.
Previous studies examining brain plasticity in amputees have focused on parts of the brain that control the functionality of an artificial limb.
This study is the first to go further – examining responses in the visual processing part of the brain, and specifically the brain areas that recognize body parts. Researchers also analyzed in the same people the connections between the visual area and the area of the brain that would be expected to control the missing hand.
They also asked people how often they used their prosthesis to do 27 routine daily activities such as zipping up a coat or taking money out of a wallet.
The study included 32 people with one hand – half of whom were born with one hand and half who had lost a hand due to amputation – and a control group of 24 people with two hands. Participants were shown images of prosthetic hands (including photos of their own prostheses) as well as real limbs while functional magnetic resonance imaging (fMRI) scan assessed participants’ neural responses.
For one-handed participants who used prostheses most often in their daily lives, this area of the brain clearly “recognized” the prostheses – including hook prostheses, which are functional but don’t look like hands, and high-tech myoelectric ones – as parts of a human body. The brain recognized them as hands.
For the control group and those who used prosthetic hands infrequently, the part of the brain that recognizes body parts showed a weak response to these photos.
Their conclusion: Brains of one-handed people can repurpose neural pathways, originally used for supporting hand function, to represent and control artificial limbs.
The study’s lead author, Tamar Makin of University College London, said this example of brain plasticity can be useful in encouraging and supporting more use of prostheses.
“If we can convince a person’s brain that the artificial limb is the person’s real limb, we could make prostheses more comfortable and easier to use. While the use of a prosthesis can be very beneficial to people with one hand, most people with one hand prefer not to use one regularly, so understanding how they can be more user-friendly could be very valuable,” he said.
Put another way, said Culham, “What can we do, not just to design prostheses but to understand what makes a prosthesis embedded in the brain and perhaps what makes them ‘embodiments’ rather than just tools or visual objects?”
One study participant who’d had one hand amputated told researchers during the study, “Logically I know my prosthesis is not my missing hand – it’s a tool, it’s a new sensation and I accepted that. The more I use my prosthesis, the more I feel like it becomes a part of me.”
The study was conducted by researchers at University College London and the University of Oxford, in collaboration with researchers from the Hebrew University of Jerusalem, Radboud University Nijmegen and Western. The study was funded by Wellcome, the European Research Council, the Royal Society, the Cogito Foundation, and the Natural Sciences and Engineering Research Council of Canada.