Elon Musk’s company, Neuralink, which specializes in brain-chip technology, allegedly subjected monkeys to “extreme suffering” during experiments that included inserting chips in the animals’ brains. The accusation was leveled by the Physicians Committee for Responsible Medicine which claims Neuralink and UC Davis committed nine violations of the federal 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 its complaint to the USDA.

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The statement continued: “These highly invasive implants and their associated hardware, which are inserted in the brain after drilling holes in the animals’ skulls, have produced recurring infections in the animals, significantly compromising their health, as well as the integrity of the research.”

Musk has said that he aims to begin human trials for the devices later this year.

The experiments in question were conducted at the University of California, Davis from 2017 to 2020. The school says that its Institutional Animal Care and Use Committee had “thoroughly reviewed and approved” the partnership with Neuralink.

“We strive to provide the best possible care to animals in our charge,” a spokesperson for the school said. “Animal research is strictly regulated, and UC Davis follows all applicable laws and regulations including those of the U.S. Department of Agriculture.”