Out of a total of 23 monkeys implanted with Elon Musk’s Neuralink brain chips at the University of California Davis between 2017 and 2020, at least 15 reportedly died.

Via Business Insider and the New York Post, the news comes from the Physicians Committee for Responsible Medicine, an animal-rights group that viewed over 700 pages of documents, veterinary records, and necropsy reports through a public records request at the university.

Neuralink was founded in 2016 with a goal of helping people recover from traumatic brain and spinal cord injuries, curing depression and other mental health disorders, and connecting humans to the internet for everything from music streaming to near-telepathic communication. The company has often touted its successes, such as a demonstration on a pig in 2020, and a 2021 video of a macaque playing Pong with its mind.

The project has attracted a great deal of interest from celebrities like Grimes and Lil Uzi Vert, and people suffering from paralysis often petition Musk on social media to be a part of human trials. Musk previously said that he hoped to begin human trials in 2021, but that goal has been pushed back to 2022. Based on the PCRM’s findings, the brain chips may be nowhere near ready.

“Pretty much every single monkey that had had implants put in their head suffered from pretty debilitating health effects,” said the PCRM’s research advocacy director Jeremy Beckham. “They were, frankly, maiming and killing the animals.”

Neuralink chips were implanted by drilling holes into the monkeys’ skulls. One primate developed a bloody skin infection and had to be euthanized. Another was discovered missing fingers and toes, “possibly from self-mutilation or some other unspecified trauma,” and had to be put down. A third began uncontrollably vomiting shortly after surgery, and days later “appeared to collapse from exhaustion/fatigue.” An autopsy revealed the animal suffered from a brain hemorrhage.

The PCRM filed a complaint with the the US Department of Agriculture on Thursday, accusing UC Davis and Neuralink of nine violations of the Animal Welfare Act. “Many, if not all, of the monkeys experienced extreme suffering as a result of inadequate animal care and the highly invasive experimental head implants during the experiments, which were performed in pursuit of developing what Neuralink and Elon Musk have publicly described as a ‘brain-machine interface,’” the group wrote in the complaint.