Researchers at the University of Texas are developing electrodes for brain implants that are more efficient at both sending and receiving electrical stimuli. These carbon-nanotube-coated electrodes could lead to neural implants that conserve battery life, reduce side effects of standard electrodes, and monitor how they affect the neurons they stimulate.

Metal electrodes are used with prosthetic devices, in brain implants to treat depression, and to quell the tremors of Parkinson's disease. Despite successes, conventional metal electrodes have significant limitations: their performance deteriorates over time and it's difficult to design electrodes that are good at sending and receiving electrical signals. The nanotube coating might allow smaller electrodes that stimulate areas of interest yet cause fewer side effects, such as stimulating other regions that lead to speech dysfunction.

Researchers led by Edward Keefer at the University of Texas' Southwestern Medical Center developed a simple method for coating electrodes with carbon nanotubes. These performed better at recording neural activity in mice and monkeys than did bare electrodes or those with other coatings. The nanotube coated electrodes also required less power to operate and provided less-noisy recordings than bare ones.

“Neural devices are good at sending electrical signals but not at receiving them,” says Ravi Bellamkonda, director of the Neurological Biomaterials and Therapeutics group at Georgia Tech. “Thus, batteries in deep-brain stimulators, implanted devices used to treat Parkinson's, last only about three years because they are constantly ‘on’.” It is useful at times to check whether or not a neuron is quiet. Hence, a feedback device that powers off when not needed could stretch battery use a few years more.

To modify the electrodes, U. of Texas' researchers placed them in a water-based solution of carbon nanotubes. Applying a small voltage to sites on the electrodes lets carbon nanotubes fix there. Other methods have required special substrates and high temperatures.

Keefer began working on the electrode coatings to advance his work on prosthetic devices that give sensory feedback. When the room lights are out, says Keefer, a person wearing a prosthetic has no way of knowing where his hand is. Prosthetics capable of providing this kind of feedback will require electrodes with electrical properties that don't decay rapidly like those of conventional electrodes.