Elon Musk's Neuralink brain chip was developed with the help of the University of Davis in California. Documents reveal that some of the monkeys underwent cranial surgeries as many as ten times before they were killed.
After the surgeries, "Bioglue" - a type of biological glue - was used to seal the holes drilled in the monkeys' skulls. In total, about 1,500 animals died, including sheep and pigs. The discovery raises difficult questions regarding the ethics of the experiments, and in particular regarding the suffering caused to the monkeys.