Robotic Third Thumb changes how hand represented in brain – study

Participants trained to use the device increasingly felt like it was a part of their body, researchers found.

Using a robotic Third Thumb can impact how the hand is represented in the brain, a new study has found.

Researchers trained people to use a robotic extra thumb and found they could effectively carry out dexterous tasks, like building a tower of blocks using the one hand.

Researchers said participants trained to use the thumb also increasingly felt like it was a part of their body.

Designer Dani Clode started developing the device, called the Third Thumb, as part of an award-winning graduate project at the Royal College of Art, seeking to reframe the way we view prosthetics, from replacing a lost function, to an extension of the human body.

She was later invited to join Tamar Makin’s team of neuroscientists at UCL who were investigating how the brain could adapt to body augmentation.

Professor Makin, lead author of the study, said: “Body augmentation is a growing field aimed at extending our physical abilities, yet we lack a clear understanding of how our brains can adapt to it.

“By studying people using Dani’s cleverly designed Third Thumb, we sought to answer key questions around whether the human brain can support an extra body part, and how the technology might impact our brain.”

The device is 3D-printed, making it easy to customise, and is worn on the side of the hand opposite the user’s actual thumb, near the little finger.

It is controlled with pressure sensors attached to the wearer’s feet, on the underside of the big toes.

They are wirelessly connected to the Third Thumb, and both toe sensors control different movements by immediately responding to subtle changes of pressure from the wearer.

Twenty participants were trained to use the device over five days for the study.

During this time, they were also encouraged to take the thumb home each day after training to use it in daily life scenarios, totalling two to six hours of wear time each day.

These participants were compared to an additional group of 10 control participants who wore a static version of the thumb while completing the same training.

Participants were trained to use the device during daily laboratory sessions focusing on tasks that helped increase the co-operation between it and their hand.

This included picking up multiple balls or wine glasses with one hand.

They learned the basics of using the thumb very quickly, while the training enabled them to successfully improve their motor control, dexterity and hand/Third Thumb co-ordination, researchers said.

The study found that participants were also able to operate the device when distracted – building a wooden block tower while doing a maths problem – or while blindfolded.

Ms Clode said: “Our study shows that people can quickly learn to control an augmentation device and use it for their benefit, without overthinking.

“We saw that while using the Third Thumb, people changed their natural hand movements, and they also reported that the robotic thumb felt like part of their own body.”

First author of the study, Paulina Kieliba, UCL Institute of Cognitive Neuroscience, said: “Body augmentation could one day be valuable to society in numerous ways, such as enabling a surgeon to get by without an assistant, or a factory worker to work more efficiently.

“This line of work could revolutionise the concept of prosthetics, and it could help someone who permanently or temporarily can only use one hand, to do everything with that hand.

“But to get there, we need to continue researching the complicated, interdisciplinary questions of how these devices interact with our brains.”

Participants’ brains were scanned before and after the training while they were moving their fingers individually.

Researchers said they found subtle but significant changes to how the hand that had been augmented with the Third Thumb was represented in the brain’s sensorimotor cortex.

Each finger is represented distinctly from the others in human brains but among the study participants, the brain activity pattern corresponding to each individual finger became more similar, the study found.

One week later, some of the participants were scanned again, and the changes in their brain’s hand area had subsided, researchers said.

This suggested the changes might not be long-term, but more research was needed to confirm this, they added.

Prof Makin added: “Evolution hasn’t prepared us to use an extra body part, and we have found that to extend our abilities in new and unexpected ways, the brain will need to adapt the representation of the biological body.”

The findings are reported in the journal Science Robotics.

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