How many times have you said to yourself ‘if I only had an extra hand’? Well, it’s increasingly looking like that wish might come true. Scientists and engineers are exploring how extra fingers and arms might augment our biological design and abilities. Or how they might provide a way to recover partial motor function following an event like a stroke.

Over the last few years a handful of efforts have explored the integration of extra digits and even entire extra arms in a noninvasive way. This means that unlike (invasive) neural prosthesis intended to be surgically implanted in a patient to restore neurological or motor function, these technologies are controlled by the user via external body signals such as the movement of the feet, or electrical signals recorded from the surface of the head using electroencephalography.

In a recent paper published in Science Robotics, researchers from University College London and the University of Oxford — neuroscientist Professor Tamar Makin, research assistant Paulina Kieliba, and PhD student Roni Maimon-Mor — teamed up with designer and engineer Danielle Clode at Dani Clode Design in London who developed a functional robotic extra thumb, and explored how the brain of users adapted to it. This is one of the first papers that focused on how biological body representation adapts to using a new digit.

Twenty healthy study participants used the robotic thumb over a period of five days. During this time participants took part in structured tasks and training in the lab, but were also encouraged to take the thumb home and use it as much as they wanted in unstructured daily tasks. The researchers tested the participants throughout the use period in a variety of ways to see how they were able to functionally use the robotic thumb, and how the usage of their biological fingers and hand was modified as a result. They also did functional magnetic resonance image (fMRI) scans of the participants’ brains to asses how the brain itself adapted and changed.

The robotic thumb is a 3D-printed supernumerary (i.e. extra digit) robotic finger that extends the natural capabilities of the biological hand. Ms. Clode explored a range of materials and fabrication methods as she iterated from one version to another. “3D-printing the design means we are able to iterate quickly, which also allows us to change the sizes of the robotic thumb when we work with clinical populations.” The thumb has two degrees of freedom — extending and flexing in one direction, and moving towards and away from the body in the other — controlled wirelessly by pressure sensors attached to the big toes of the feet.

One limitation of the initial design that the team is addressing is that because of the way the thumb needs to be controlled by the toes, usage is restricted to being in a static standing or sitting position. Users can’t be walking at the same time.

During training sessions in the lab, users were challenged with a variety of single-handed tasks that required the users to integrate the robotic thumb. This forced the biological fingers and extra robotic thumb to necessarily work together. And forced the brain to adapt so it could coordinate the necessary motor commands. The users were able to quickly learn basic tasks and then carry out increasingly difficult ones that put further cognitive demands on the brain.

The researchers also tested the subjective sense of embodiment that the extra thumb created. Participants who were actively using the robotic thumb reported increased levels of embodiment — that is, feeling that the thumb had become a part of them. In addition, they also demonstrated increased proprioception — the sense of position — over the thumb. Interestingly, this did not extend to a control group who had a non-functioning robotic thumb.

Usage of the extra thumb also changed how the fingers of the biological hand were used relative to each other. In other words, the coordination patterns between the biological fingers when the robotic thumb was being used was different than how the fingers cooperated when the robotic thumb wasn’t present. They weren’t just using their hand as they normally would but with an extra thumb.

Yet, additional implicit cognitive testing showed that despite these effects, the robotic thumb did not change or alter the individual’s implicit perception of their own body image when the thumb wasn’t present. The internal cognitive model and perception of their bodies remained the same as before any exposure to the extra thumb.

The researchers were also interested in understanding how an abrupt change in how people use their hands in daily life impacts the brain’s representation of the hands. This links to their ongoing interest in studying brain plasticity following amputation.

Contrary to popular accounts, according to Prof. Makin, the paper’s senior author, the brain retains its internal representation of lost limbs. It does not fade away and other body parts do not take over those parts of the brain. Even decades later. As Prof. Makin put it: “Nothing much changes in the brain if you take out the hand. The representation of the hand and each and everyone of the fingers is persistent in the brain”.

However, while taking a hand or fingers away doesn’t change the brain, adding a finger does. It’s a reflection of brain plasticity.

Similar to the users reporting an increased sense of embodiment when the robotic thumb was present, there was a measurable effect on the brain and how it internally represented, or mapped, the biological fingers of the augmented hand with the robotic thumb. The researchers focused on studying parts of the motor cortex, which controls hand movements, among other functions. The parts of the brain that encoded the augmented hand changed the representation of individual fingers and the relationships between them when compared to the non-augmented hand as a control. The brain’s representation of the fingers on the augmented hand shrunk when compared to the non-augmented hand.

There are many important questions scientists still need to answer. The overarching question of interest to Prof. Makin is “given a fully occupied motor system (in the brain), how do you make room for an extra hand”? And “how do you send motor commands to control an extra body part, without impairing your own body and without taking up too much cognitive load?”

These questions are important, because as the authors pointed out in their paper: “Successful adoption of augmentative technologies relies not only on the user’s proficiency in operating the robotic device. A further challenge for augmentation is to ensure that the device usage will not influence the users’ ability to control their biological body, especially when the augmentative device is not being used or even worn. Therefore, a critical question for safe motor augmentation is whether it would incur any changes to the user’s biological body representation.” Addressing these considerations are important not just for the design of such technologies but for their safe and effective adoption.

Beyond studying and understanding brain plasticity, there are practical and immediate needs temporary and reversible augmentation technologies can support. For example, allowing people to continue working and being productive if they break an arm, which is extremely costly economically. The advantage, as Ms. Clode pointed out, is that “this kind of temporary augmentation is very robust given how quickly people can learn to control it; not a lot of training is needed to gain basic function.”

Prof. Makin also commented that in addition, another important demographic is “the aging population, which given fragility fractures, the impact of temporary disability gets much worse.” Other populations this technology will be able to help that the researchers are exploring include amputees, stroke patients, and even individuals who were born with a hand difference.

This technology can also be used in work forces — from surgeons who need to hold and manipulate multiple tools, to other manual jobs where an additional finger, or even arm, can allow individuals to complete their work more efficiently.

Looking even further, there could be potential applications beyond the augmentation of healthy individuals or clinical populations, aimed at extending the reach of humans in more inhospitable environments such as space. Ms. Clode’s perspective is that “it’s a way to engage with technology to extend our physical bodies to do the touching and grabbing for you. We won’t be doing it with our biological hands. So it’s important to understand the impact something like this will have if you use it everyday, then take it off. How will it impact your brain? How will you form a relationship with the technology?”

In Prof. Makin’s words: “I take augmentation very seriously. If it’s done correctly at this stage it will revolutionize humanity. It has the potential to completely change and transform the way we interact with our environment. And it’s as true in your kitchen as it would be taking a space walk”.

This article was originally published on Forbes.com. You can check out this and other pieces written by the author on Forbes here.

An Extra Robotic Thumb Quickly Changes How The Brain Represents And Uses Its Biological Hand was originally published in AR/VR Journey: Augmented & Virtual Reality Magazine on Medium, where people are continuing the conversation by highlighting and responding to this story.