Today's neural implants shut down chronic pain, stave off epileptic seizures and aid thousands of people worldwide who have hearing problems. Tomorrow, they could help patients regain control of limbs or allow brains to connect with computers "Matrix"-style. But existing devices can also cause jangling pain in nearby nerves as they send out electrical signals in the moist human brain.
Now MIT researchers have figured out how to stimulate target nerves with less collateral pain for part-human, part-machine cyborgs. By tweaking the electrical balance of fluids surrounding a nerve, they could still trigger a nerve using much less electrical current. They also figured out how to use less current to stop electrical impulses traveling along nerves — a step that could help shut off the haywire electrical storm patterns of epilepsy or ease chronic pain.
"I'm sure that this technology will form the basis of many future neuroprosthetic devices," said Peter Kjall, project leader of the organic bioelectronics group at the Swedish Medical Nanoscience Center.
Kjall did not take part in the MIT research, but he praised the technology for its potential to make even current-generation neural implants more efficient. The MIT team slashed the amount of electrical current needed by about 70 percent.
Using less electrical current matters because the nerves that control facial movements end up bunched together with sensory nerves that transmit pain. Researchers came up with the solution of manipulating the fluid concentrations of charged atoms or molecules, called ions, so that less electrical current could still trigger certain target nerves without bothering the neighboring nerves.
"The problem is that the electricity can go everywhere, because our bodies are conductors," said Jongyoon Han, associate professor of electrical engineering and computer science and biological engineering at MIT.
To do that, Han and his colleagues coated neural implant electrodes with a membrane that filters out certain ions in the fluid surrounding target nerves. They now hope to apply their technique to neural implants that can manipulate muscles with damaged nerves.
"Functional electrical stimulation, as an idea, has been around for a long time, but its implementation in our body as a prosthetic is still in its infancy," Han said.