Monkey Feels Touch with New Prosthetic Limb: Breakthrough for Amputees

Prosthetic limbs are becoming more and more advanced over time. We're learning how to make individual fingers move through sheer brain power or flex artificial legs in the same way. Now, though, scientists have made a breakthrough when it comes to prosthetic limbs. They've laid the groundwork for touch-sensitive limbs that could one day convey real-time sensory information to amputees via a direct interface with the brain.

"To restore sensory motor function of an arm, you not only have to replace the motor signals that the brain sends to the arm to move it around, but you also have to replace the sensory signals that the arm sends back to the brain," said Sliman Bensmaia, one of the researchers, in a news release. "We think the key is to invoke what we know about how the brain of the intact organism processes sensory information, and then try to reproduce these patterns of neural activity through stimulation of the brain."

Currently, the scientists are working specifically on the sensory aspects of these limbs. So far, they've conducted a series of experiments with monkeys. Within these animals, they identified patterns of neural activity that occur during natural object manipulation and then successfully induced these patterns through artificial means.

The first of these experiments focused on contact location. Essentially, this is what you feel when something touches your skin; you know exactly where you've been touched. The monkeys were trained to identify several patterns of physical contact with their fingers. Then, the scientists connected electrodes to areas of the brain corresponding to each finger and replaced the physical touches with electrical stimuli. In the end, the monkeys responded the same way to the artificial stimulation as they did to real physical contact.

Next was to focus on the sensation of pressure and contact events. In the end, the scientists were able to use electrical signals to get the monkeys to respond the same way that they would if they experienced the real sensation.

"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," said Bensmaia in a news release. "When it is, the functionality of these limbs will increase substantially."

The findings could potentially help researchers develop prosthetic limbs that can not only move, but can actually feel. This could help greatly improve the quality of life for amputees.

The findings are published in the Proceedings of the National Academy of Sciences.