Monkeys being used in experiments conducted by Elon Musk’s Neuralink company suffered from rampant infection, severe distress, and were sometimes euthanised after being implanted with experimental hardware that Musk claims will one day let humans “save and replay memories”.

The Physicians Committee for Responsible Medicine (PCRM) raised the concerns with US animal welfare authorities and has began a lawsuit against the University of California, where the experiments were taking place.

It claims Neuralink and its academic partners at the university were negligent in their treatment of the animals, deviated from the approved experimental protocols, and tried to cover up the mistreatment of monkeys.

“The documents reveal that monkeys had their brains mutilated in shoddy experiments and were left to suffer and die,” Jeremy Beckham, a researcher with the PCRM, said in a statement.

“It’s no mystery why Elon Musk and the university want to keep photos and videos of this horrific abuse hidden from the public.”

Distressing reports based on veterinary records describe how some monkeys began self-mutilating after being implanted with Neuralink’s devices, that they were often distressed and had been given anti-depressants or anti-anxiety medication, and frequently had infections around where the devices were implanted into their skulls that didn’t properly heal.

Veterinary records also show that monkeys were treated with ‘Bioglue’, a substance that was not approved for use in the experiments and which the PCRM claims destroyed parts of the monkeys brains when it was applied.

In court papers, the PCRM alleges the University of California deliberately withheld documentation about the experiments, initially claiming it was not in the public interest.

It then claimed Neuralink had removed all evidence of the experiments from university property, including videos.

“They did not tell us why they were taking [videos],” the university said. “We do not know what storage media Neuralink used to store them on but, in all events, the media were Neuralink property.

“They provided their own computing infrastructure and they had their own network connection, and they have removed their computing infrastructure from the premises.”

The PCRM disagreed that evidence about experiments was not in the public interest, especially given Neuralink’s own publicity exercises that included trotting out pigs and showing video footage of a monkey called Pager playing the game Pong with a chip in its brain.

Neuralink has responded to the PCRM’s claims, saying in a blog post that the accusations “come from people who oppose any use of animals in research”.

“Currently, all novel medical devices and treatments must be tested in animals before they can be ethically trialled in humans,” Neuralink said.

“Neuralink is not alone in this regard.”

But the PCRM has said experimenting on non-human primates “is a subject of great ethical concern” because of their “high degree of sentience”.

Neuralink is preparing for clinical trials of its devices in humans and was, as of January, searching for a director to head up that process.

Musk’s company has lofty aims for its brain-computer interface devices, including to give people with severe disabilities the option of controlling a smart phone with their thoughts.

Musk has suggested more out-there future uses of his devices such as saving and recording memories – something neuroscientists are highly skeptical about given the immense amount of information stored in the hardware of a single human brain and how difficult it is to decipher that information from the outside.