People equipped with an additional, robotic thumb learned to control it with their toes – but prolonged used may come at a cost of their brains being less certain about how their hands work.
Danielle Clode at University College London and her colleagues gave 36 people a prosthetic thumb that wrapped around their wrist and sat underneath their little finger. All were right-handed, and wore the device on their dominant hand.
The third thumb’s movement was controlled by sensors attached to the user’s big toes, and communications were sent using wireless technology affixed at the wrist and ankle. By wiggling each toe, the augmented humans could move the thumb in different directions and clench its grip.
For five days, participants were encouraged to use the thumb both in laboratory settings and in the wider world. “One of the goals of the training was to push the participants about what was possible and train them in unique new ways of handling objects,” says Clode.
The additional thumb could cradle a cup of coffee while the same hand’s forefingers held a spoon to stir in milk, for instance, while some participants used the thumb to flick through pages of a book they were holding in the same hand. The average user wore the thumb for just under 3 hours a day.
To understand how the extra thumb affected people’s brains, the researchers gave them an MRI scan before and after the experiment.
“Technology is advancing, but no one is talking about whether our brain can deal with that,” says team member Paulina Kieliba, also at UCL.
“In our augmented population, on the right hand, the representation of individual fingers collapsed on each other,” says Kieliba – meaning the brain perceived each finger as more similar to each other than it did before the experiment. A week later, 12 of the participants returned for a third brain scan, where the effect of the brain changes had begun to wear off.
Jonathan Aitken at the University of Sheffield, UK, is surprised at how quickly participants adapted to the thumb. “The incorporation of such an unfamiliar tool – and one that requires operation by the toes to control action – and the rapid speed of learning is very interesting,” he says.
Journal reference: Science Robotics, DOI: 10.1126/scirobotics.abd7935
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