Assuming you have the medical technology to reconnect the spinal chord and/or sensory nerves, but all else otherwise is the same as present-day medical state of the art?
(This is inspired by an old movie I saw, long ago, and it’s something I’ve been meaning to ask about. Plus, it’s almost Halloween, so…y’know, it seemed appropriate. And yes, I know the proper terminology should really be “body transplant,” but this gets to the point.)
I think I recall reading in some of Dr. Robert White’s research that there would be less immune system complications to deal with when just transplanting (or grafting) a brain, but I don’t know the details. And I have a hard time believing that that’d stack up favorably against the complications of manhandling a brain into another skull, hooking up said nerve and vascular connections, and while keeping it hooked to a life support system, without killing it.
Of course, there may be reasons we don’t know about yet, seeing as how we don’t know how to do the transplant at all yet.
I think it’s at least plausible that immune system rejection is easier with just a brain: I understand the brain is somewhat walled off from the rest of the body (there are drugs that will affect most of the body, but won’t get through the blood-brain barrier).
If I had to come up with fanwanking type reasons for a brain-only transplant (i.e. reasons I don’t actually think are very likely, but are just barely possible with some suspension of skepticism), a couple might be:
Turns out that keeping the entire airway (mouth/nose, trachea, vocal cords, lungs) together makes it easier for the transplanted brain to learn to speak.
The spinal column and skull (and associated muscles) need to be more or less intact to work well together. Splicing a new skull onto the spine always results in back problems and coordination issues.
Most of the cranial nerves - there are about a dozen of them - connect the brain directly to things in the head (eyes, mouth, ears, nose, facial muscles, etc.). If you did a complete head transplant you would avoid the need to reconnect these. I rather suspect that reconnecting nerves (which are all multi-strand cables) correctly would be one of the most challenging parts of any such surgery. (Of course, either way you are going to have to reconnect the spinal cord and the vagus nerve correctly.)
Head transplant, you have to keep your own face, which might be o0ld and ugly. With a brain transplant, you might be able to trade your face in for a newer and better looking one.
Part of this I’ve been wondering about, for awhile—even if the brain tissue is somewhat walled off from the immune system, how far does this extend to things immediately connected to the brain, like it’s own blood vessels, or the dura?