Brain-Computer Interface Industry Comes to Surface

by James Cavuoto, editor

The relatively young brain-computer interface industry, which in recent years gained notoriety using penetrating electrodes to interface with cortical neurons, is moving toward electrodes placed on the surface of the brain. Much of the impetus for this change has been the demise of Cyberkinetics, the Foxboro, MA manufacturer that closed its doors earlier this year. Blackrock Microsystems of Salt Lake City, UT acquired much of Cyberkinetics’ BCI product base, including the NeuroPort system.

The University of Utah, which developed the original penetrating electrode array marketed by Cyberkinetics, is now developing an array of miniature electrocorticographic electrodes for BCI applications. Bradley Greger, an assistant professor of bioengineering, and colleagues published a study in this month’s issue of Neurosurgical Focus. The findings represent “a modest step” toward use of the new microelectrodes in systems that convert the thoughts of amputees and paralyzed people into signals that control lifelike prosthetic limbs, computers, or other devices, says University of Utah neurosurgeon Paul House, the study’s lead author. The new study was funded partly by the DARPA’s bionic arm project, and by the National Science Foundation and Blackrock Microsystems, which provided the system to record brain waves.

Existing, penetrating electrode arrays are undesirable over critical brain areas that control speech and memory, and they 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.

Traditional ECoG electrodes used in epilepsy surgery are placed 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. 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 Utah researchers designed and tested microECoGs in two severe epilepsy patients who already were undergoing craniotomies.

The researchers tested how well the microelectrodes could detect nerve signals from the brain that control arm movements. The two epilepsy patients sat up in their hospital beds and used one arm to move a wireless computer “mouse” over an electronic draftsman’s tablet in front of them. The patients were told to reach their arm to one of two targets: one was forward to the left and the other was forward to the right. The patients’ arm movements were recorded on the tablet and fed into a computer, which also analyzed signals coming from the microelectrodes placed on the area of each patient’s brain controlling arm and hand movement.

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.

The first patient received two identical arrays, each with 16 microelectrodes arranged in a four-by-four square. Individual electrodes were spaced 1 millimeter apart. Patient 1 had the ECoG and microECoG implants for a few weeks. The findings indicated the electrodes were so close that neighboring microelectrodes picked up the same signals.

Months later, the second patient received one array containing about 30 electrodes, each 2 millimeters apart. This patient wore the electrode for several days. “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.

Earlier this year, Neurolutions Inc., a St. Louis, MO startup firm, announced they would pursue a BCI based on ECoG recording. Ascension Health Ventures of St. Louis participated in the Neurolutions financing along with BioGenerator, also a St. Louis-based venture fund. Neural Signals Inc., which developed the first commercial implanted BCI, now also markets an EMG sensor called Libertas Switch.