Brains can be kept alive in isolation

Keeping brains alive in vitro has been possible since the sixties. Part one of the prerequisites for "biological AI" seems to be mostly solved.

Robert J White on head transplantation.

Brain transplantation (Warning: mildly gory/sensationalist article): "... Dr White managed to keep the isolated brain alive for days, proving not only that the brain could survive away from its own body but that it was immunologically sound - meaning that, unlike a kidney, it could be transplanted without the likelihood of the new 'body' rejecting it."

Even Wikipedia has an article on head transplants.