Enough that it is not considered a viable approach for general purpose BCIs in adult subjects. You can get away with injecting one to study or affect a small lo

Enough that it is not considered a viable approach for general purpose BCIs in adult subjects. You can get away with injecting one to study or affect a small localized region, but that's about it [source: chat with a Lieber lab collaborator]. Unless of course you get Cultured and put it in place at the embryonic stage, so the brain grows into it.