February 16, 2017

Smoother Electrodes May Improve BCIs

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Photograph of the glassy carbon electrodes, courtesy of SDSU.

When people suffer spinal cord injuries and lose mobility in their limbs, the brain can still send clear electrical impulses and the limbs can still receive them, but the signal gets lost in the damaged spinal cord. Researchers at the Center for Sensorimotor Neural Engineering (CSNE)—a collaboration of San Diego State University (SDSU) with the University of Washington (UW) and the Massachusetts Institute of Technology (MIT)—are working on an implantable brain-computer interface (BCI) that can record neural electrical signals and transmit them to receivers in the limb, bypassing the damage and restoring movement. BCIs can also be used to power prosthetic limbs. Recently, these researchers described an improvement to the technology that could make it more durable, last longer in the body, and transmit clearer, stronger signals. The study was published in the journal Scientific Reports.

The BCI records and transmits signals through electrodes, which read signals from brain chemicals known as neurotransmitters. By recording brain signals at the moment a person intends to make some movement, the BCI learns the relevant electrical signal pattern and can transmit that pattern to the limb’s nerves, or even to a prosthetic limb, restoring mobility and motor function. The current material for electrodes in BCIs is thin-film platinum. The problem is that these electrodes can fracture and fall apart over time, said one of the study’s lead investigators, Sam Kassegne, PhD, PE, deputy director for the CSNE at SDSU and a professor in the mechanical engineering department.

Kassegne and colleagues developed electrodes made out of glassy carbon. This material is about ten times smoother than granular thin-film platinum, meaning it corrodes less easily under electrical stimulation and lasts longer than platinum or other metal electrodes.

“Glassy carbon is much more promising for reading signals directly from neurotransmitters,” Kassegne said. “You get about twice as much signal-to-noise. It’s a much clearer signal and easier to interpret.”

The glassy carbon electrodes are fabricated on the SDSU campus. The process involves patterning a liquid polymer into the correct shape, then heating it to 1,000 degrees Celsius, causing it to become glassy and electrically conductive. Once the electrodes are cooled, they are incorporated into chips that read and transmit signals from the brain and to the nerves. Researchers in Kassegne’s lab are using these new and improved BCIs to record neural signals along the brain’s cortical surface and from inside the brain at the same time.

“If you record from deeper in the brain, you can record from single neurons,” said Elisa Castagnola, PhD, one of the researchers. “On the surface, you can record from clusters. This combination gives you a better understanding of the complex nature of brain signaling.”

Editor’s note: This story was adapted from materials provided by SDSU.

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