March 30, 2011

BCI System Reaches 1,000-Day Performance Milestone

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BrainGate uses a 4x4 mm silicon electrode array to read neural signals directly within brain tissue. Photographs courtesy of BrainGate Collaboration.

An investigational implanted system known as BrainGate*, being developed by researchers at Brown University (Brown), Providence, Rhode Island, to translate brain signals toward control of assistive devices has allowed a woman with tetraplegia to accurately control a computer cursor 2.7 years after implantation, according to a Brown press release. This demonstrates an important milestone for the longevity and utility of implanted brain-computer interfaces (BCIs), according to a team of physicians, scientists, and engineers developing and testing the technology at Brown; the Providence Veterans Affairs (VA) Medical Center, Rhode Island; and Massachusetts General Hospital (MGH), Boston.

Results from five consecutive days of device use surrounding her 1,000th day in the device trial appeared online March 24 in the Journal of Neural Engineering. Report findings have implications for better control of advanced prosthetic limbs.

“This proof of concept—that after 1,000 days a woman who has no functional use of her limbs and is unable to speak can reliably control a cursor on a computer screen using only the intended movement of her hand—is an important step for the field,” Brown associate professor of engineering, VA rehabilitation researcher, visiting associate professor of neurology at Harvard Medical School, Boston, Massachusetts, and director of the BrainGate pilot clinical trial at MGH, Leigh Hochberg, MD, PhD, said.

The woman, identified in the paper as S3, performed two “point-and-click” tasks each day by thinking about moving the cursor with her hand. In both tasks she averaged greater than 90-percent accuracy. Some on-screen targets were as small as the effective area of a Microsoft Word menu icon.

“Our objective with the neural interface is to reach the level of performance of a person without a disability using a mouse,” report lead author, VA researcher, and assistant professor of engineering at Brown, John Simeral, PhD, said. “These results highlight the potential for an intracortical neural interface system to provide a person that has locked-in syndrome with reliable, continuous point-and-click control of a standard computer application.”

A woman with paralysis controls a computer cursor on a screen by the neural activity of intending to move it with her arm and hand. She used the investigational BrainGate system more than 1,000 days after the device was implanted.

Under development since 2002, the investigational BrainGate system is a combination of hardware and software that directly senses electrical signals produced by neurons in the brain that control movement. By decoding those signals and translating them into digital instructions, the system is being evaluated for its ability to provide people with paralysis control of external devices such as computers, robotic assistive devices, or wheelchairs. The BrainGate team is also engaged in research toward control of advanced prosthetic limbs and toward direct intracortical control of functional electrical stimulation (FES) devices for people with spinal cord injury, in collaboration with researchers at the Cleveland FES Center, Ohio.

BrainGate uses a 4x4 mm silicon electrode array to read neural signals directly within brain tissue. Although external sensors placed on the brain or skull surface can also read neural activity, they are believed to be far less precise. In addition, many prototype brain implants have eventually failed because of moisture or other perils of the internal environment.

“Neuroengineers have often wondered whether useful signals could be recorded from inside the brain for an extended period of time,” Hochberg said. “This is the first demonstration that this microelectrode array technology can provide useful neuroprosthetic signals allowing a person with tetraplegia to control an external device for an extended period of time.”

Device performance was not the same at 2.7 years as it was earlier on, Hochberg added. At 33 months, fewer electrodes were recording useful neural signals than after only six months. But John Donoghue, PhD, VA senior research career scientist, Henry Merritt Wriston, professor in the Department of Neuroscience, director of the Brown Institute for Brain Science and original developer of the BrainGate system, said no evidence has emerged of any fundamental incompatibility between the sensor and the brain. Instead, it appears that decreased signal quality over time can largely be attributed to engineering, mechanical, or procedural issues. Since S3’s sensor was built and implanted in 2005, the sensor’s manufacturer has reported continual quality improvements. The data from this study will be used to further understand and modify the procedures or device to further increase durability.

“None of us will be fully satisfied with an intracortical recording device until it provides decades of useful signals,” Hochberg said. “Nevertheless, I’m hopeful that the progress made in neural interface systems will someday be able to provide improved communication, mobility, and independence for people with locked-in syndrome or other forms of paralysis and eventually better control over prosthetic, robotic, or functional electrical stimulation systems, even while engineers continue to develop ever-better implantable sensors.”

In addition to demonstrating the longevity of the BrainGate sensor, the paper also presents an advance in how the performance of a brain-computer interface can be measured, Simeral said. “As the field continues to evolve, we’ll eventually be able to compare and contrast technologies effectively.”

In addition to Simeral, Hochberg, and Donoghue, study authors include BrainGate research team members Michael Black, PhD, director of the Max Planck Institute for Intelligent Systems (Stuttgart, Germany), Perceiving Systems Department, and adjunct professor (research), Brown, Department of Computer Science; and S. Phil Kim. PhD, postdoctoral research associate in the Brown Department of Computer Science, and assistant professor at the Department of Brain and Cognitive Engineering, Korea University, Seoul, South Korea.

*Investigational device. Limited by federal law to investigational use.

Editor’s note: This story has been adapted from materials provided by Brown University.

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