Researchers Turn to "Spare" High-Frequency Neural Capacity to Drive Additional Robotic Limbs
The discovery of low- and high-frequency motor neuron signals provides a path for easily controlling additional limbs.
Researchers at Imperial College London and the University of Freiburg, working alongside other members of the Non-invasive Interface for Movement Augmentation (NIMA) project, are looking to give you a leg up — by, potentially, giving you an addition leg, or arm, or thumb, or other limb, controlled using spare neural capacity.
"What could you do with an extra limb? Consider a surgeon performing a delicate operation, one that needs her expertise and steady hands — all three of them. As her two biological hands manipulate surgical instruments, a third robotic limb that's attached to her torso plays a supporting role," the research team, including senior author Dario Farina, write in a joint piece for IEEE Spectrum on their work.
"Or picture a construction worker who is thankful for his extra robotic hand as it braces the heavy beam he's fastening into place with his other two hands," the team continues. "Imagine wearing an exoskeleton that would let you handle multiple objects simultaneously, like Spider-Man's Dr. Octopus. Or contemplate the out-there music a composer could write for a pianist who has 12 fingers to spread across the keyboard."
While the proposed use-cases are, perhaps, currently more science-fiction than science-fact, it's a future the team is aiming to see created — working with the NIMA project to drive human augmentation to new levels. Simply strapping a robotic limb to a person, though, isn't enough — you need a way to control it that doesn't involve tying up your existing limbs, rendering the addition more of a hindrance than a help.
In the team's most recent work, it details a wearable system for monitoring the spiking activity of motor neurons across two frequencies. The low frequency band is responsible for actually making the muscle move, while the high frequency band is not — allowing subjects in the test to trigger the sensor and move external devices without causing their legs to do the same. "Results indicate that beta projections to the spinal motor neuron pool can be voluntarily controlled partially decoupled from natural muscle contractions," the researchers explain, "and, therefore, they could be valid control signals for implementing effective human motor augmentation platforms."
The team found that the test subjects were able to learn to control the seemingly-useless high-frequency signals independently of the muscle-moving low-frequency signals — but admits that "control was not accurate enough for practical use," with improving the accuracy a key part of future work ahead of using it to control an actual robotic supernumerary limb.
More information is available in the IEEE Spectrum article, while details of the dual-frequency motor neuron experiment have been published in the Journal of Neural Engineering under open-access terms.