From curing depression and obesity to possessing telepathy, Elon Musk promised that the future of humanity would look significantly different once his dream of a revolutionary brain implant to treat intractable conditions such as paralysis and blindness is realized. On at least four separate occasions since 2019, he predicted that his medical device company, Neuralink, would soon start human trials of the brain chips.

Yet the company, founded in 2016, didn’t seek permission from the U.S. Food and Drug Administration (FDA) until early 2022 – and the agency rejected the application, seven current and former employees told Reuters.

The rejection has not been previously reported. However, in explaining the decision to Neuralink, the agency outlined dozens of issues the company must address before human testing, a critical milestone on the final product approval, the staffers said. The agency’s major safety concerns involved the device’s lithium battery; the potential for the implant’s tiny wires to migrate to other areas of the brain; and questions over whether and how the device can be removed without damaging brain tissue, the employees said.

A year after the rejection, Neuralink still addresses the agency’s concerns. However, three staffers said they were skeptical the company could quickly resolve the issues – despite Musk’s latest prediction at a Nov. 30 presentation that it would secure FDA human-trial approval this spring.

Neuralink has not disclosed details of its trial application, the FDA’s rejection, or the extent of the agency’s concerns. As a private company, disclosing such regulatory interactions to investors is not required. During the hours-long November presentation, Musk said the company had submitted "most of our paperwork" to the agency specifying no formal application. Nevertheless, neural link officials acknowledged the FDA had asked safety questions in what they characterized as an ongoing conversation.

Musk and other Neuralink officials did not respond to requests for comment on the company’s device or its dealings with the FDA. The agency declined to comment on Neuralink, citing laws keeping commercial information private.

The Neuralink sources declined to provide Reuters with the agency’s written rejection, a legally confidential document. Instead, the staffers, including four who had read the FDA document and others aware of the agency’s concerns, described the safety issues in interviews, speaking anonymously.

Such FDA rejections do not mean a company will fail to gain the agency’s human-testing approval. But the agency’s pushback signals substantial concerns, according to more than a dozen experts in FDA device-approval processes.

Neuralink’s regulatory struggles stem primarily from its culture of setting goals for breakthroughs on extremely ambitious timelines and viewing regulators as obstacles to innovation, according to more than a dozen current and former company employees. In addition, the staffers say that leadership style, mirroring how Musk runs electric-car pioneer Tesla, can create vulnerabilities when applied to developing a medical device that must be tested on human subjects before final approval.

In public comments over the years, Musk has detailed a bold vision for Neuralink: Both disabled and healthy people will pop into neighborhood facilities for quick surgical insertions of devices with functions ranging from curing obesity, autism, depression, or schizophrenia to web-surfing and telepathy.

Musk also has said Neuralink would restore full mobility to paralyzed patients. In February, Dongjin "D.J." Seo, Neuralink’s vice president of engineering, said at a conference that the "primary short-term goal" was more modest: to help paralyzed patients communicate through computerized text without typing. Seo said full mobility, along with restoring sight to the blind, were "long-term" goals.

Neuralink’s focus on speed has contributed to other problems. Reuters reported late last year that the federal government was investigating the company’s treatment of its research animals. The probe was launched amid growing employee concern that the company is rushing experiments, causing additional suffering and deaths of pigs, sheep, and monkeys. Three Neuralink staffers now tell Reuters that company leaders wanted animal experiments accelerated to gather data to address FDA concerns over the human-trial application.

Safety concerns

The FDA’s rejection listed dozens of what the agency calls "deficiencies" that the company must address before human trials, five Neuralink sources said. However, they called some issues relatively minor.

One serious FDA concern involved the possibility that the device’s tiny threads, which carry electrodes, could migrate to other brain areas, according to six current and former employees. The company has sought to address the issue through animal tests on dozens more pigs, three Neuralink sources said.

Migrating wires can induce inflammation, impair function in critical areas of the brain and rupture blood vessels, said Victor Krauthamer, a former FDA official for three decades, including a stint as acting director of the office that reviews human-trial requests for brain implants. He and other experts said that a migration problem could also erode the device’s effectiveness, leading to the risk of surgical removal.

"The threads can cause damage because brains are very, very soft and very delicate," Krauthammer said.

The FDA’s concerns about the battery are also potentially serious, experts in brain devices said. Neuralink proposed making its device with a novel charging system involving lithium batteries that could be recharged remotely. However, the agency found the company needed to show in animal studies that the battery was unlikely to fail, six current and former Neuralink employees said. In addition, three brain-implant experts said that if any device component connected to the battery current falls, the wind could potentially damage brain tissue.

The FDA also questioned whether the device could be removed without damaging brain tissue. In Neuralink’s November presentation, officials acknowledged the FDA concern but downplayed it.

The FDA also flagged concerns that the device could overheat, potentially damaging tissue.

Neuralink may be able to address all the FDA’s concerns, industry and regulatory experts said.

The experts said that if the FDA has minor issues with a company’s device, it might let the firm move forward with a slower, staged trial. According to two people familiar with the discussions, the agency has suggested that such a path might work for Neuralink, with fewer subjects implanted at first and more tested months later.

Still, one of the sources said that that proposal disappointed Neuralink because it could delay progress toward final FDA approval.

"The reason we don’t have a (BCI) device yet like Neuralink’s is not that no one has spent any money on it," Gene Civillico, a neurophysiologist who formerly worked for both the FDA and the NIH on neural-implant research, said.

"It’s not because Elon Musk hasn’t thought about it enough. It’s because it’s a hard problem."