"The FDA’s rejection listed dozens of what the agency calls “deficiencies” that the company must address before human trials, five Neuralink sources said. They called some issues relatively minor.

One serious FDA concern involved the possibility that the device’s tiny threads, which carry electrodes, could migrate to other areas of the brain, according to six current and former employees."

U.S. regulators rejected Elon Musk’s bid to test brain chips in humans https://www.reuters.com/investigates/special-report/neuralink-musk-fda/