Despite the development of cutting-edge technologies in the field of prosthetics, artificial limbs don’t yet offer the full functionality of biological ones. To address this challenge, scientists and engineers have been focusing on improving wearable technology with the help of robotics and artificial intelligence. Enter the notion of embodiment, where an external object is controlled by the brain as one’s real body part. This is crucial for better integrating artificial parts into the human body.
Researchers partially supported by the EU-funded EmbodiedTech project have revealed how prosthetic limbs are represented like real hands in the brain. Their study could guide rehabilitation strategies for amputees and help the implementation of future augmentation technologies.
The findings were recently published in the journal ‘Brain’
. The study included 32 people with a missing hand – half of whom were born with one hand and half who had lost a hand due to amputation – alongside 24 people with two hands used as a control group. The participants were shown images of prosthetic hands, including photos of their own prostheses, as well as real limbs. Their neural responses were assessed by functional magnetic resonance imaging which involves the measurement of brain activity by detecting changes associated with blood flow.
Explaining the study in a news release
by University College London (UCL), Dr Tamar Makin said: “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.” Dr Makin, who is an associate professor at the UCL Institute of Cognitive Neuroscience, added: “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.”
The researchers observed that among participants with prostheses, the neural responses in the brain’s visual cortex area that enables people to recognise hands were stronger than those of the control group. This was particularly the case for one-handed participants who used their prostheses frequently in their daily lives. As the researchers explained in the journal article: “We show that the more one-handers use an artificial limb (prosthesis) in their everyday life, the stronger visual hand-selective areas in the lateral occipitotemporal cortex respond to prosthesis images.” This part of the brain also responded to images of prostheses that are functional but do not look like a hand, such as a hook prosthesis.
The researchers also analysed the neural connections between the separate brain areas that enable people to recognise hands and control them. They found that there was better connectivity between these two brain areas in people who used their prostheses regularly. This indicates that the brain had reprogrammed itself.
Quoted in the UCL news release, journal article co-author Fiona M.Z. van den Heiligenberg, said: “Our findings suggest that the key determinant of whether the brain responds similarly to a prosthetic hand as it does to a real hand is prosthetic use. As many of our study participants lost their hand in adulthood, we find that our brains can adapt at any age, which goes against common theories that brain plasticity depends on development early in life.”
The ongoing EmbodiedTech (Can humans embody augmentative robotics technology?) project examines the conditions necessary for technological embodiment using prosthetic limbs as a model.
For more information, please see:EmbodiedTech project