could a severed head theoretically be reattached?

I mean a human head. And have the person live on? Could you switch heads? Brains? Why would this be so much different from putting together an arm or a leg?

Head Transplant. Sort of, but not very well at the moment.

In principle, I would think so, but it would be an astonishingly complex operation and you’d have a very short time to complete it before the patient died; if the brain is not oxygenated it dies pretty quickly. Plus, your patient would be at best quadriplegic; once the spinal column has been transected, I don’t think you acheive very much by rejoining it.

You probably can but brain cells would have been dead cellularly before you can complete the operation.

OK, this is blatantly wrong. Is there something about evidence that this board doesn’t like? I posted the Wikipedia article that goes into great depth about the procedure. The transplant can be done well enough. We can’t (at the moment) connect the spinal cord, so no control of the body. When it’s been done, the victim - that is, subject - often dies of infection, but transplanted dog heads have lived up to 29 days.

But your evidence relates to head transplants, in which a head is only severed for the purposes of transplant, and arrangements have been made in advance to keep the head alive during the operation. The OP asks about a “severed head” with no context, and of course most severing of human heads does not arise in the context of planned transplant surgery. If a human head is severed in an accident or in a execution by beheading, can it be reattached? No; it will die very quickly. Even if we could successfully carry out a human head transplant operation, we still wouldn’t be able to reattach human heads severed in the circumstances in which, in practice, human heads are severed.

OK, sure. I guess I just read the question as doing a transplant for the normal reasons you do transplants: An organ is failing and you need a new one. In this case, the “organ” is instead the whole body, but same principle.