Ars chats with Precision, the brain-chip maker taking the road less invasive

Work toward brain-computer interfaces has never been more charged. Though neuroscientists have toiled for decades to tap directly into human thoughts, recent advances have the field buzzing with anticipation—and the involvement of one polarizing billionaire has drawn a new level of attention.

With competition amping up in this space, Ars spoke with Ben Rapoport, who is a neurosurgeon, electrical engineer, and co-founder of the brain-computer interface (BCI) company Precision Neuroscience. Precision is at the forefront of the field, having placed its BCI on the brains of 14 human patients so far, with two more scheduled this month. Rapoport says he hopes to at least double that number of human participants by the end of this year. In fact, the 3-year-old company expects to have its first BCI on the market next year.

In addition to the swift progress, Precision is notable for its divergence from its competitor's strategies, namely Neuralink, the most high-profile BCI company and headed by Elon Musk. In 2016, Rapoport co-founded Neuralink alongside Musk and other scientists. But he didn't stay long and went on to co-found Precision in 2021. In previous interviews, Rapoport suggested his split from Neuralink related to the issues of safety and invasiveness of the BCI design. While Neuralink's device is going deeper into the brain—trying to eavesdrop on neuron signals with electrodes at close range to decode thoughts and intended motions and speech—Precision is staying at the surface, where there is little to no risk of damaging brain tissue.

Shallow signals

"It used to be thought that you needed to put needle-like electrodes into the brain surface in order to listen to signals of adequate quality," Rapoport told Ars. Early BCIs developed decades ago used electrode arrays with tiny needles that sink up to 1.5 millimeters into brain tissue. Competitors such as Blackrock Neurotech and Paradromics are still developing such designs. (Another competitor, Synchron, is developing a stent-like device threaded into a major blood vessel in the brain.) Meanwhile, Neuralink is going deeper, using a robot to surgically implant electrodes into brain tissue, reportedly between 3 mm and 8 mm deep.

However, Rapoport eschews this approach. Anytime something essentially cuts into the brain, there's damage, he notes. Scar tissue and fibrous tissue can form—which is bad for the patient and the BCI's functioning. "So, there's not infinite scalability [to such designs]," Rapoport notes, "because when you try to scale that up to making lots of little penetrations into the brain, at some point you can run into a limitation to how many times you can penetrate the brain without causing irreversible and undetectable damage."

Further, he says, penetrating the brain is just unnecessary. Rapoport says there is no fundamental data that suggests that penetration is necessary for BCIs advances. Rather, the idea was based on the state of knowledge and technology from decades ago. "It was just that it was an accident that that's how the field got started," he said. But, since the 1970s, when centimeter-scale electrodes were first being used to capture brain activity, the technology has advanced from the macroscopic to microscopic range, creating more powerful devices.

"All of conscious thought—movement, sensation, intention, vision, etc.—all of that is coordinated at the level of the neocortex, which is the outermost two millimeters of the brain," Rapoport said. "So, everything, all of the signals of interest—the cognitive processing signals that are interesting to the brain-computer interface world—that's all happening within millimeters of the brain surface ... we're talking about very small spatial scales." With the more potent technology of today, Precision thinks it can collect the data it needs without physically traversing those tiny distances.

Staying above it all

Precision's device, called the Layer 7 Cortical Interface, uses electrode arrays on a yellow film, described as one-fifth the thickness of a human hair, which contains 1,024 electrodes ranging in diameter from 50 to 380 microns. The arrays are designed to slip harmlessly onto the surface of the brain through a slit in the skull that could be less than 1 mm deep. The name is a nod to the six layers of cells in the brain responsible for higher-order functions. The placement of the array does require cutting through the dura—a membrane around the brain—which could develop scarring, Rapoport said. But this scarring is not in the brain tissue itself and is usually a few centimeters away from where the electrodes sit.

The array is connected to a customized hardware interface that is implanted on the outside of the skull under the scalp. In its design, Rapoport emphasized the importance of scalability, allowing multiple arrays to be included in the device. Just last month, the company announced a world-record use of 4,096 electrodes on a human patient with the Layer 7 Cortical Interface.

So far, the device has been used in patients who are having brain surgery for other reasons—a low-risk, early-stage approach. For instance, in March, The Wall Street Journal was present as a patient undergoing neurosurgery to relieve Parkinson's symptoms had the Layer 7 placed on his brain for 25 minutes. In that surgery—at Pennsylvania Hospital in Philadelphia—the patient used a motion-capture glove and made a series of hand movements as the device recorded his brain activity. The patient was also told to imagine making hand movements without actually moving his hand so that the device could record activity related merely to intention.

"We have, basically, time-synchronized movement of the hand intention of the patient and the physiologic readout on the motor cortex, and that allows us to confirm [not only] that we can interpret what the brain is intending to do, but what the brain is telling the hand to do before it tells the hand to do it, right. And that's in a patient who obviously can move their hand, because our end target users will not be able to move their hand. And, so, that gives us a data set that is just incredibly rich, gold-standard for confirming that our system can do what we're intending to do."

The near future

In future designs, Rapoport is excited to use more arrays to cover more areas of the brain, combining brain activity related not only to movement, but also things like cognitive pre-planning and sensory feedback. "Being able to have a modular, scalable ability to deploy [electrodes] over multiple functional regions, we feel, is really, really important."

Along with the movement-based work being done in collaboration with researchers at Penn Medicine, Precision is conducting similar movement-related studies with Mount Sinai Health System. And at West Virginia University’s Rockefeller Neuroscience Institute, Precision has partnered with researchers to calibrate the Layer 7 to decode speech in patients who are undergoing surgery to remove tumors near brain regions responsible for language.

The cautious clinical work allows Precision to validate and verify all the aspects of the device—the sensing array, the electronics, and the decoding software—while also getting a glimpse of potential pitfalls. "It's been very important for us to make sure that we encounter whatever the real-world issues are as early as possible before a design lock on the complete system," Rapoport said.

As work continues on the lofty goals of allowing paralyzed patients to control computers and other devices with their minds, Precision is working on a temporary, wire-based version of the Layer 7 for early clearance by the Food and Drug Administration. This first-generation BCI could be used to map brain activity at high resolution ahead of surgeries. Less sophisticated but similar devices are already on the market, so Precision hopes to get the regulatory green light relatively swiftly. "We anticipate being the first brain-computer interface company to have an FDA-cleared product," Rapoport said.