I recall in a sci-fi Asimov book, it was related to the 2001 series, there was a skull cap that everyone wore in the 3000's that once placed on your head was permanent as its tendrils weaved its way into your scalp. They were like nano-scale. That idea, although completely sci-fi, seems pretty awesome as there would be more direct input if the entire surface area of your brain was a read-write interface. Also that is scary in terms of abuse.