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Reading the Brain without Poking it
Arrays of tiny electrodes placed
between the skull and the brain;
© University of Utah
Experimental devices that read brain signals have helped paralyzed people use computers and may let amputees control bionic limbs. But existing devices use tiny electrodes that poke into the brain.
"The unique thing about the new technology is that it provides lots of information out of the brain without having to put the electrodes into the brain," says Bradley Greger, an assistant professor of bioengineering. "That lets neurosurgeons put this device under the skull but over brain areas where it would be risky to place penetrating electrodes: areas that control speech, memory and other cognitive functions."
Not only are the existing, penetrating electrode arrays undesirable for use over critical brain areas, but the electrodes likely wear out faster if they are penetrating brain tissue rather than sitting atop it, Greger and University of Utah neurosurgeon Paul A. House say.
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.
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.
The study showed that the microECoG electrodes could be used to distinguish brain signals ordering the arm to reach to the right or left, based on differences such as the power or amplitude of the brain waves.
The microelectrodes were formed in grid-like arrays embedded in rubbery clear silicone. The arrays were over parts of the brain controlling one arm and hand.
"We were trying to understand how to get the most information out of the brain," says Greger. The study indicates optimal spacing is 2 to 3 millimeters between electrodes, he adds.
MEDICA.de; Source: University of Utah