Neuralink President Max Hodak tweeted Saturday that he has left the company he co-founded with Tesla and SpaceX CEO Elon Musk xxx. Hodak didn’t elaborate on why he left the company or elaborate on the circumstance for his departure. “I am no longer at Neuralink (as of a few weeks ago),” he tweeted. “I learned a ton there and remain a huge cheerleader for the company! Onward to new things.”

Neuralink is focused on developing brain-machine interfaces. Last month, the company posted a video to YouTube that appeared to show a monkey with a Neuralink implant in its brain moving a cursor on a computer screen using only its mind.

Musk and Hodak founded Neuralink along with several other people in 2016, and Musk has invested millions of dollars of his own money into the venture. Last year, Stat News reported that some former employees described a chaotic internal culture at Neuralink, saying that its scientists weren’t always given enough time to complete projects.

While Neuralink didn’t invent brain-machine interfaces, its technology includes thin, flexible wires and more electrodes than other devices, potentially providing more data. Musk has stated that Neuralink’s technology could one day be used to allow paraplegics to walk again and allow humans to achieve “AI symbiosis,” merging the human brain with an artificial intelligence.

But some in the scientific and medical communities have criticized Neuralink and are skeptical of its scientific claims; after an August 2020 demonstration of a pig that had a Neuralink device implanted in its brain, MIT Technology Review called the company “neuroscience theater,” and said “most of the company’s medical claims remain highly speculative.”

And as The Verge’s Nicole Wetsman wrote last year, “fixing the brain isn’t an engineering problem.” Scientists need to learn much more about how the brain works before any of the concepts Musk describes can come to pass, she added. “The brain is still mysterious, and the neurological causes of things like anxiety and addiction are still unclear,” Wetsman wrote.

Hodak didn’t immediately reply to a request for comment Sunday.