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Each year prosthetic limbs become more incredible, whether they allow a wearer to run at Olympic speeds or are controlled by thought alone. But most still lack a sense of touch, which would give the wearer greater control and connection to their prosthetic limb.

University of Chicago researchers have published a paper detailing how stimulating a prosthetic limb wearer’s brain with electrical signals could replicate feelings of touch. They worked with monkeys, which they outfitted with electrodes connected to different areas of the brain associated with touch. The researchers studied their brain’s response to different types of touch to pinpoint the type and amount of electrical signal that would best replicate the sensation.

The monkeys went through several touch exercises with their normal hand and an unstimulated brain. The same exercises were conducted with a prosthetic hand, which was equipped with pressure sensors to register instances of touch. Pressure registered by the hand was converted into electrical signals, which the electrodes delivered to the monkeys’ brains.

The researchers found that the monkeys responded the same in both situations. This includes when the monkeys first touched or released an object, sensing pressure and identifying where on their finger they touched an object — all important facets of touch.

The researchers hold that touch is an essential addition to prosthetic limbs. While some limbs can take in signals from the brain to control movement, they aren’t really complete until they can also send signals back to the brain.

“The algorithms to decipher motor signals have come quite a long way, where you can now control arms with seven degrees of freedom. It’s very sophisticated. But I think there’s a strong argument to be made that they will not be clinically viable until the sensory feedback is incorporated,” assistant professor Sliman Bensmaia said in a release. “When it is, the functionality of these limbs will increase substantially.”

The researchers have yet to test the system in humans. The system would also need to become more sophisticated before a person could incorporate it into their daily life, when it would have to judge and replicate sensations of touch for a much wider range of activities.