There's a big difference between "does this thing work" and "does this thing kill you". Trials for the former are moot at this point, because it doesn't matter

There's a big difference between "does this thing work" and "does this thing kill you". Trials for the former are moot at this point, because it doesn't matter if it works if it turns you into a vegetable. Making a safe device and a safe way to implant it is really the only concern at this point, because you can always change how the device works later if it doesn't do the thing but also doesn't hurt you. Trials for the second are still important to be done safely. Plenty of people diagnosed as terminally ill are misdiagnosed. Just this week, the story about plutonium told of the Manhattan project injecting terminally ill folks with plutonium to see what it did. One of them turned out not to be terminally ill. A procedure like this also feels mutually exclusive with any sort of real palliative care, which feels like a really terrible thing to do to someone who is dying. You don't have a lot of terminally ill folks up and walking around, living a normal life. It's not just about not killing someone, either. Brain implants can cause horrifying effects: intense pain, confusion, hallucinations, memory issues, and more. None of these folks will have any tangible benefit from being implanted with these test devices (the killer app, no pun intended, seems to be "hands free pong"). And yet, there's a risk that the last remaining days (or not!) are filled with irrecoverable torment, and that starts to bring up questions of euthanasia. How many people are you willing to have to put into a chemically induced coma and euthanize because you didn't do enough animal testing first, even if those folks were maybe going to die anyway?