Robotic ‘Third Thumb’ Changes How Hand is Represented in Brain

A team of researchers at the University College London (UCL) has demonstrated how a robotic ‘Third Thumb’ can change how the hand is represented in the brain. Individuals were trained to use a robotic extra thumb, and it enabled them to do dexterous tasks with one hand with two thumbs. 

According to the researchers’ report, the participants increasingly felt like the Thumb was part of their body. 

Changing the Way We View Prosthetics 

The device is called the Third Thumb, and it was developed as part of a postgraduate project at the Royal College of Art. The project is aimed at changing the way we view prosthetics, seeing these technologies as an extension of the human body rather than a replacement. 

Designer Dain Clode first began developing the device before joining Professor Tamar Makin’s team of neuroscientists at UCL. The team was investigating how the brain can adapt to body augmentation. 

Professor Makin was lead author of the study. 

“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,” Makin says. “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 Third Thumb is 3D-printed, which means it can be customized. It is worn on the side of the hand that is opposite of the user’s thumb, and it is controlled by the user through pressure sensors attached to the underside of their feet. The sensors are wireless connected to the Thumb, and both of them control different movements of the Thumb by responding to pressure changes from the user.

The Study 

The study involved 20 participants that were trained to use the device over a five-day period. They were encouraged to take it home and use it in day-to-day life, which resulted in two to six hours of wear time each day. Those 20 participants were compared to an additional group of 10 control participants who wear a static version of the device.

The training involved tasks that helped increase cooperation between the hand and the Thumb, including picking up multiple balls or wine glasses with one hand. The users demonstrated an ability to learn quickly, and the training helped them successfully improve their motor control, dexterity and hand-Thumb coordination. 

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

Body Augmentation

Paulina Kieliba is first author of the study. 

“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,” Kieliba says. “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.”

Through fMRI scans, the researchers found significant changes to how the augmented hand was represented in the brain’s sensorimotor cortex. The changes did not seem to be long-term, as scans one week later showed that the changes in their brain’s hand area had subsided. 

“Our study is the first one investigating the use of an augmentation device outside of a lab. It is the first augmentation study carried over multiple days of prolonged training, and the first to have an untrained comparison group,” Kieliba said. “The success of our study shows the value of neuroscientists working closely together with designers and engineers, to ensure that augmentation devices make the most of our brains' ability to learn and adapt, while also ensuring that augmentation devices can be used safely.”

“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,” Makin added.