Earlier this year, the US Food and Drug Administration gave Neuralink, which Musk cofounded in 2016, approval to launch human trials of its device that Musk has described as a “Fitbit in your skull.” The FDA had previously rejected Neuralink’s bid for human testing in March over safety concerns, Reuters reported, including that the wires connected to the brain chip could move within a subject’s head or that the chip could overheat.