Brain-computer interfaces have managed some amazing feats: allowing paralyzed people to type words and move a robot using only their minds, to name two examples. Brown University neuroengineering professor Arto Nurmikko has had a hand in some of those developments, but even he says the technology is at only a rudimentary stage—the equivalent of the computer understanding the brain’s intention to bend a single finger.

“We’re trying to go from the bending-of-the-finger paradigm to tying shoe laces and even to the concert pianist level. That requires lots more spatial and temporal resolution from an electronic brain interface,” Nurmikko says. His team is hoping that kind of resolution will come along with the transition from a single, hard wired neural implant to a thousand or more speck-size neural implants that wirelessly communicate with computers outside the brain. At the IEEE Custom Integrated Circuits Conference, engineers from Brown University, Qualcomm, and the University of California San Diego presented the final part of a communications scheme for these implants. It allows bidirectional communication between the implants and an external device with an uplink rate of 10 megabits per second and a downlink rate of 1 Mb/s.

“We believe that we are the first group to realize wireless power transfer and megabits per second communications” in a neural implant, says Wing Ching (Vincent) Leung, technical director at the Qualcomm Institute Circuits Lab at UC San Diego.

Nurmikko calls the 0.25-square-millimeter implants “neurograins.” They each consist of a chip capable of harvesting RF energy; that chip powers an electrode that senses spikes of voltage from individual neurons, as well as the wireless communications. An antenna set outside of the skull provides the RF power, transmits to the implants, and receives data from them.

Neurograin chips contain a coil-shaped on-chip antenna at their perimeters. The antenna surrounds uplink and downlink circuits that transmit and receive at megabits per second data rates. Neurograin chips contain a coil-shaped on-chip antenna at their perimeters. The antenna surrounds uplink and downlink circuits that transmit and receive at megabits-per-second data rates.Image: UC San Diego

Permitting a thousand implants to talk to the same external antenna created some difficult downlink problems for the neurograins team to solve. For one, the neurograins had no way to coordinate their on-chip clocks with each other. For another, they all receive slightly different amounts of power, but they don’t carry a reliable voltage reference for comparing to the highs and lows of incoming bits.

“We had to form a synchronized network with no common reference and no clock between the nodes, and do it with low power and small area,” says Leung.

The answer came in the form of a purpose-built low-power voltage comparator and a communications scheme called amplitude-shift keying with pulse-width modulation. In that scheme, bits are represented as a change in amplitude in a pattern that depended on how long that change lasted. Each bit has both a high and low portion. A “1” has a high pulse that lasts twice as long as the low pulse portion that follows it, and a “0” is high for half as long as the low-amplitude portion that follows. This ensures that the bits are still identifiable even though none of the neurograins’ 30-megahertz clocks are synched together and there isn’t a reliable voltage reference with which to compare their signals.

Leung and Nurmikko’s team had already worked out other aspects of the communications system. Using the new downlink scheme, the part of the system that resides outside of the head powers the neurograins and then addresses each one in series, commanding them to upload data at 10 Mb/s. Under this arrangement, a thousand neurograin implants can all have their say in the space of 100 milliseconds. 

The team says it has one remaining task: integrating the neural recording and stimulation circuitry. But even with that addition, Leung expects neurograins to be reduced to 0ne-tenth of their current size, which would make implantation less invasive.

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Restoring Hearing With Beams of Light

Gene therapy and optoelectronics could radically upgrade hearing for millions of people

13 min read
A computer graphic shows a gray structure that’s curled like a snail’s shell. A big purple line runs through it. Many clusters of smaller red lines are scattered throughout the curled structure.

Human hearing depends on the cochlea, a snail-shaped structure in the inner ear. A new kind of cochlear implant for people with disabling hearing loss would use beams of light to stimulate the cochlear nerve.

Lakshay Khurana and Daniel Keppeler
Blue

There’s a popular misconception that cochlear implants restore natural hearing. In fact, these marvels of engineering give people a new kind of “electric hearing” that they must learn how to use.

Natural hearing results from vibrations hitting tiny structures called hair cells within the cochlea in the inner ear. A cochlear implant bypasses the damaged or dysfunctional parts of the ear and uses electrodes to directly stimulate the cochlear nerve, which sends signals to the brain. When my hearing-impaired patients have their cochlear implants turned on for the first time, they often report that voices sound flat and robotic and that background noises blur together and drown out voices. Although users can have many sessions with technicians to “tune” and adjust their implants’ settings to make sounds more pleasant and helpful, there’s a limit to what can be achieved with today’s technology.


8 channels


64 channels

Since optogenetic therapies are just beginning to be tested in clinical trials, there’s still some uncertainty about how best to make the technique work in humans. We’re still thinking about how to get the viral vector to deliver the necessary genes to the correct neurons in the cochlea. The viral vector we’ve used in experiments thus far, an adeno-associated virus, is a harmless virus that has already been approved for use in several gene therapies, and we’re using some genetic tricks and local administration to target cochlear neurons specifically. We’ve already begun gathering data about the stability of the optogenetically altered cells and whether they’ll need repeated injections of the channelrhodopsin genes to stay responsive to light.

Our roadmap to clinical trials is very ambitious. We’re working now to finalize and freeze the design of the device, and we have ongoing preclinical studies in animals to check for phototoxicity and prove the efficacy of the basic idea. We aim to begin our first-in-human study in 2026, in which we’ll find the safest dose for the gene therapy. We hope to launch a large phase 3 clinical trial in 2028 to collect data that we’ll use in submitting the device for regulatory approval, which we could win in the early 2030s.

We foresee a future in which beams of light can bring rich soundscapes to people with profound hearing loss or deafness. We hope that the optical cochlear implant will enable them to pick out voices in a busy meeting, appreciate the subtleties of their favorite songs, and take in the full spectrum of sound—from trilling birdsongs to booming bass notes. We think this technology has the potential to illuminate their auditory worlds.

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