Researchers at the University of Chicago are working on new technology for touch-sensitive prosthetic limbs that one day could 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 the study’s senior author, Sliman Bensmaia, PhD, assistant professor in the department of organismal biology and anatomy at the University of Chicago. “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.”
Bensmaia’s research is part of Revolutionizing Prosthetics, a multi-year Defense Advanced Research Projects Agency (DARPA) project that seeks to create a modular, prosthetic arm that will restore natural motor control and sensation in amputees.
In a series of experiments with monkeys, the researchers identified patterns of neural activity that occur during natural object manipulation and then successfully induced these patterns through artificial means.
The first set of experiments focused on contact location. The animals were trained to identify several patterns of physical contact with their fingers. Researchers then connected electrodes to areas of the brain corresponding to each finger and replaced physical touches with electrical stimuli delivered to the appropriate areas of the brain. The animals responded the same way to artificial stimulation as they did to physical contact.
Another experiment focused on pressure sensation. Researchers developed an algorithm to generate the appropriate amount of electrical current to elicit a sensation of pressure. The animals’ response was the same whether the stimuli were felt through their fingers or through artificial means.
Bensmaia and his colleagues also studied sensation of contact events. Researchers used electrical stimulation to replicate brain activity that occurs when the hand touches and releases an object.
The result of the research is a set of instructions that can be incorporated into a robotic prosthetic arm to provide sensory feedback to the brain through a neural interface. Bensmaia believes such feedback will bring these devices closer to being tested in human clinical trials.
“The algorithms to decipher motor signals have come quite a long way, where you can now control arms with seven degrees of freedom. But I think there’s a strong argument to be made that they will not be clinically viable until the sensory feedback is incorporated,” Bensmaia said in a press release. “When it is, the functionality of these limbs will increase substantially.”
For more information:
Tabot G. PNAS. doi: 10.1073/pnas.1221113110.