Rather than building a device from the ground up, Synchron and Paradromics took inspiration from previous medical devices. For example, Paradromics' design is based on the Utah array, but makes some significant improvements. For example, it is wireless and has 421 electrodes at the end of small wires that are embedded in the brain tissue. Those wires are all much smaller than the shafts of the Utah array, Angle says.
Synchron's device, meanwhile, is a hollow mesh tube that resembles a cardiac stent. Instead of going directly into the brain, it is inserted into the jugular vein at the base of the neck and pressed against the cortex. Synchron has implanted ten participants with its device to date, one of whom has been using it for more than three years. (Arbaugh's implant still works after 100 days). Banerjee says the company has not seen any decline in signal quality or performance.
Andrew Schwartz, a professor of neurobiology at the University of Pittsburgh who builds interfaces between brains and computers, also speculates that Neuralink's design may have pushed the implanted wires out of the brain.
The outermost layer of the brain, the dura, must be opened to insert the device. “Because multiple wires are individually inserted into the cortex, it can be difficult to suture the dura closed after implanting the wires,” he says. If you had left this opening, it could have caused scar tissue to form around the opening, causing the wires to retract. The Utah array, Schwartz says, is designed so that the dura can be sutured closed after implantation.
Despite Neuralink's setback, the company still succeeded livestream a demonstration of his device on March 20, with Arbaugh using the implant to play chess just by thinking about it. Arbaugh also used the device to play the video game Mario Kart. “I just can't even describe how cool it is to be able to do this,” he says said in the video.
In the blog post, Neuralink says it has compensated for the lost threads by adjusting the recording algorithm so that it is more sensitive to neural signals. It also says that it has improved the way it translates these signals into cursor movements and improved the user interface, and that these changes may have improved the device's performance.
For moving a cursor, Angle says having more electrodes doesn't make much of a difference. But for more complex tasks, such as converting text to speech, a higher data rate will be important.
Before getting the implant, Arbaugh used a mouth-held stylus, also called a mouth stick, to operate a tablet that had to be put into place by a caregiver. A mouth stick can only be used in an upright position and prevents normal speech. When used for extended periods of time, it can cause discomfort, muscle fatigue and pressure sores.
For Arbaugh, Neuralink's device is a “luxury overload,” according to the company's blog post. He still uses the implant, which allows him to “reconnect with the world” and do things for himself again without needing his family around the clock.
“It is good that the patient can still use the device and is still happy with it. Ultimately, that's a win,” Angle said. “But from our perspective, companies building brain-computer interfaces need to build devices that are robust and reliable over a multi-year period.”
There are likely to be setbacks on the road to commercializing brain-computer interfaces, and with Neuralink taking a unique approach with its device, the company could encounter even more setbacks along the way.