Researchers from the Johns Hopkins University’s Applied Physics Laboratory (APL) and School of Medicine (SOM) have, for the first time, demonstrated simultaneous control of two of the world’s most advanced prosthetic limbs through a brain-machine interface. The team is also developing strategies for providing sensory feedback for both hands at the same time using neural stimulation.

“We are trying to enable a person with quadriplegia to use a direct neural interface to simultaneously control two assistive devices and, at the same time, feel touch sensation when the devices make contact with objects in the environment,” said Dr. Brock Wester, a biomedical engineer and APL’s principal investigator for the study.

“[This advance] has significant implications for restoring capabilities to patients with high spinal cord injuries and neuromuscular diseases” he said. “For everything we envision people needing or wanting to do to become independent — tie their shoes, catch and throw a ball, squeeze toothpaste onto a toothbrush — they really need two hands working together.”

These breakthroughs are the latest developments in Revolutionizing Prosthetics (RP), a program launched by the Defense Advanced Research Projects Agency in 2006 to rapidly improve upper-extremity prosthetic technologies and provide new means for users to operate them.

The original vision of the RP program was to create a neurally integrated prosthetic upper limb with human-like capabilities; this resulted in the Modular Prosthetic Limb (MPL). “As we integrated new capabilities into the MPL, such as fingertip sensors for force, acceleration, slip and pressure, we started to ask ourselves, ‘what is the best way to feed this information back to our study participants so that they would be able to interact with the environment just as able-bodied people do?’” said Dr. Francesco Tenore, APL project manager.

In addition to developing the MPL, program researchers have been exploring the use of neural signals to enable “real time” control of prosthetic and intelligent systems. The program’s initial neural control studies with participants at the University of Pittsburgh and the California Institute of Technology/Rancho Los Amigos focused on the control of a single limb, which three participants were able to do after months of training. This success highlighted the possibilities of neuroprosthetics and laid the groundwork for future studies.

APL is working with two research groups at The Johns Hopkins Hospital: Dr. Pablo Celnik’s team in Physical Medicine and Rehabilitation and Dr. Nathan Crone’s team in the Department of Neurology.