BCIs (brain-computer interfaces) are a new type of assistive technology that could one day allow people with brain or spinal injuries move or communicate. Implantable sensors capture electrical impulses in the brain and use those signals to control external devices such as computers or robotic prosthesis in BCI systems.
The majority of existing BCI systems use one or two sensors to sample up to a few hundred neurons, but neuroscientists are interested in systems that can collect data from far larger groups of neurons.
Now, a group of researchers has taken a significant step toward a novel notion for a future BCI system: one that records and stimulates brain activity using a coordinated network of independent, wireless microscale neural sensors, each approximately the size of a grain of salt. The “neurograins” sensors record the electrical pulses produced by firing neurons individually and communicate the signals wirelessly to a central hub, which coordinates and interprets the signals.
The research team showed the use of nearly 50 such independent neurograins to record brain activity in a rodent in a study published on August 12 in Nature Electronics.
The findings, according to the researchers, represent a step toward a technology that could one day allow for the unprecedented recording of brain impulses, leading to new insights into how the brain operates and new therapies for those with brain or spinal injuries.
“Engineering ways to probe as many sites in the brain as feasible is one of the main difficulties in the field of brain-computer interfaces,” said Arto Nurmikko, a professor in Brown’s School of Engineering and the study’s senior author. “Most BCIs have been monolithic devices up to this point, resembling little needle beds. Our plan was to dismantle the monolith into small sensors that could be scattered throughout the cerebral cortex. That’s exactly what we’ve been able to show here.”
The team, which comprises members from Brown University, Baylor University, the University of California in San Diego, and Qualcomm, began working on the system four years ago. According to Nurmikko, who is linked with Brown’s Carney Institute for Brain Science, the problem was twofold. The initial step was to compress the complicated electronics used to detect, amplify, and transmit neural impulses into small silicon neurograin chips. To produce functioning chips, the team first developed and simulated the circuitry on a computer, then proceeded through numerous fabrication rounds.
The body-external communications hub that accepts messages from those tiny chips was the second challenge. The gadget is a tiny patch that attaches to the scalp outside the skull and is roughly the size of a thumb print. It functions similarly to a miniature cellular phone tower, using a network protocol to coordinate signals from the neurograins, each of which has its own network address. The patch also provides wireless power to the neurograins, which are designed to run on very little electricity.
Jihun Lee, a postdoctoral researcher at Brown and the study’s lead author, remarked, “This work was a truly multidisciplinary challenge.” “To build and run the neurograin system, we needed to bring together knowledge in electromagnetics, radio frequency communication, circuit design, fabrication, and neurology.”
The purpose of this new research was to show that the device could record neural impulses from a living brain, specifically a rodent’s brain. The researchers implanted 48 neurograins in the cerebral cortex of the animal, which is the brain’s outer layer, and successfully captured distinctive neural signals linked to spontaneous brain activity.
The scientists also examined the devices’ ability to both stimulate and record from the brain. Small electrical pulses are used to activate brain activity during stimulation. Researchers hope that the stimulation, which is controlled by the same hub that controls neural recording, will one day be able to restore brain function that has been lost due to disease or injury.
The researchers was limited to 48 neurograins for this investigation due to the size of the animal’s brain, but the data suggests that the system’s current setup might support up to 770. The team hopes to eventually scale up to tens of thousands of neurograins, providing a hitherto unreachable picture of brain activity.
“It was a difficult undertaking,” said Vincent Leung, an associate professor in Baylor’s Department of Electrical and Computer Engineering. “The system requires simultaneous wireless power transfer and networking at the megabit-per-second rate, and this has to be accomplished under extremely tight silicon area and power constraints.” “In terms of distributed neural implants, our team pushed the envelope.”
There’s still a lot of work to be done to make that whole system a reality, but the researchers believe this study is a big step in the right way.
“We hope to eventually establish a system that delivers new scientific insights into the brain as well as new therapies that can help those who have suffered severe injuries,” Nurmikko added.