Meanwhile, researchers at the University of Utah and elsewhere are working on a $55 million Pentagon project to develop a lifelike bionic arm that war veterans and other amputees would control with their thoughts, just like a real arm. Scientists are debating whether the prosthetic devices should be controlled from nerve signals collected by electrodes in or on the brain, or by electrodes planted in the residual limb.

Microelectrodes May Last Longer


Not only are the existing, penetrating electrode arrays undesirable for use over critical brain areas that control speech and memory, but the electrodes likely wear out faster if they are penetrating brain tissue rather than sitting atop it, Greger and House say. Nonpenetrating electrodes may allow a longer life for devices that will help disabled people use their own thoughts to control computers, robotic limbs or other machines.

"If you're going to have your skull opened up, would you like something put in that is going to last three years or 10 years?" Greger asks.

"No one has proven that this technology will last longer," House says. "But we are very optimistic that by being less invasive, it certainly should last longer and provide a more durable interface with the brain."

The new kind of array is called a microECoG - because it involves tiny or "micro" versions of the much larger electrodes used for electrocorticography, or ECoG, developed a half century ago.

For patients with severe epileptic seizures that are not controlled by medication, surgeons remove part of the skull or cranium and place a silicone mat containing ECoG electrodes over the brain for days to weeks while the cranium is held in place but not reattached. The large electrodes -- each several millimeters in diameter -- do not penetrate the brain but detect abnormal electrical activity and allow surgeons to locate and remove a small portion of the brain causing the seizures.

ECoG and microECoG represent an intermediate step between electrodes that poke into the brain and EEG electroencephalography, in which electrodes are placed on the scalp. Because of distortion as brain signals pass through the skull and as patients move, EEG isn't considered adequate for helping disabled people control devices.

The regular-size ECoG electrodes are too large to detect many of the discrete nerve impulses controlling the arms or other body movements. So the researchers designed and tested microECoGs in two severe epilepsy patients who already were undergoing craniotomies.

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