Neuralink gets FDA green light for second patient, as first describes his emotional journey

The fixes include embedding some of the device’s ultrathin wires deeper into the brain, according to a person familiar with the company and a document viewed by The Wall Street Journal.

As Neuralink prepares for its second test participant, the first, Noland Arbaugh, is opening up about the impact of the device on his life and the emotional roller coaster he experienced before, during and after the device lost part of its functionality.

In the days after his January implantation, Arbaugh used the Neuralink implant to control a cursor on a computer screen with only his thoughts. A quadriplegic with no movement below his shoulders for the past eight years, Arbaugh suddenly was able to communicate with friends, play games and interact with his world in ways that hadn’t seemed possible after his accident.

But a month after his surgery, he noticed the device was no longer working as well. Most of the threads implanted in his brain had come loose and were no longer reading the electrical signals needed to translate his thoughts into cursor movements.

“I was on such a high and then to be brought down that low. It was very, very hard," Arbaugh said in an interview. “I cried."

Neuralink’s N1 implant is a container about the size of a U.S. quarter that holds electronics and a battery. Its 64 external threads, each thinner than a human hair, are inserted into the brain’s motor cortex to relay neural signals.

Arbaugh said that Neuralink has told him around 15% of the threads inserted in his brain remain in place. But these have stabilized, he said, and software changes made by the company later helped him regain many of the device’s capabilities, which he has since demonstrated in livestreams.

Since such a device had never been implanted in a human before, Neuralink didn’t know how much the brain would move inside the skull, said Arbaugh. It found that his brain moved up to three times what the company expected, he said.

To keep threads in place, one of Neuralink’s proposed solutions that the FDA has signed off on is to implant them eight millimeters into the brain’s motor cortex, compared with about three-to-five millimeters for Arbaugh.

With the FDA’s blessing, Neuralink now hopes to implant a second participant some time in June, according to the person familiar with the company, who said that more than 1,000 quadriplegics have signed up for its patient registry, though fewer than 100 qualify for the study.

And while some of those people are eligible, Musk posted on X on Thursday that the company is still accepting applications.

Neuralink aims to implant 10 people with its device this year and hopes to have a diverse set of recipients in order to study a variety of behaviors. One challenge is that the people signing up to its patient registry skew white and male, the person said.

Neuralink hopes to submit applications to regulators in Canada and Britain in coming months to start similar trials in those countries, the person said. Its patient registry is open for Canada and will be opening for Britain in the coming days.

When Arbaugh learned why his implant had stopped responding to his thoughts, he said, he asked if it could be removed and fixed, or possibly replaced. A team that included three Neuralink staff had just broken the news to him in his hotel a mile from Neuralink’s California headquarters, which he was scheduled to tour after driving up from Arizona with his family. Arbaugh’s medical team said they didn’t want to do another brain surgery and preferred to wait for more information, he recalled.

“I thought that I had just gotten to, you know, scratch the surface of this amazing technology, and then it was all going to be taken away," he said. “But it only took me a few days to really recover from that and realize that everything I’ve done up to that point was going to benefit everyone who came after me."

A few weeks after disclosing the problem to Arbaugh, Neuralink was still trying to figure out exactly what had happened. But Arbaugh described in the interview how the company’s engineers improved the performance of his own device, altering how it decoded his brain signals.

It concentrated on clumps of neurons providing a strong signal and switched off many of the electrodes receiving weaker or no signals. In a blog post earlier this month, the company said it modified its recording algorithm “to be more sensitive to neural population signals."

That improved things to the point that Arbaugh said he has now surpassed the capabilities he’d had before the threads retracted. “It makes me very, very hopeful for the future," he added in the interview. “It seems like we’ve learned a lot and it seems like things are going in the right direction."

Write to Rolfe Winkler at Rolfe.Winkler@wsj.com