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If your brain is removed, and a new brain is installed in your body, you have effectively vacated the premises.

Were a brain transplant feasible, it would be more accurate to describe it as a body transplant. The brain "donor" would actually be the beneficiary of the procedure, in contrast to the usual transplant scenario.

One wonders if this might become an option, in the future, for people suffering from the catastrophic failures of multiple organs. Rather than hope for the availability of compatible replacements, one could simply evacuate their body entirely and take up residence in a new one. This raises, of course, the question of who exactly would be willing to donate his or her body to someone else and face life as a disembodied brain.

Let's get some extropians working on this.

The brain transplant (sometimes called a "body transplant" on the notion that it represents transplantation of every part of you which may be changed out while you remain "you") is the Holy Grail of organ transplants, the ultimate in brain surgery. A successful feat would encompass removal of a living human brain from one living human body, and situation of it in a new living human body. Thus might the actual memory, conscience, and personality of the person whose original body it was transplanted from continue to live for, at the least, some indeterminate future period beyond what the original body would have allowed. The most exciting proposition is how near we are to realising virtually all of the lesser technological steps which would make this achievement a practical possibility.

To wit: transplant technology generally has proved successful for almost every other organ in the body, and medical techniques for stabilisation of the donor and recipient bodies and transference of organs between them has become highly developed. At least some brain tissue transplantation has effectively been done with mice (loathe though I am for animal experimentation, at least it's not for mere cosmetic benefit), though there has yet to be a successful whole brain transplant in any species, nor a definitive situation wherein the recipient of the transplanted matter has been proved to retain memories of the donor.

The brain differs from any other part of the body, for those particular mysteries of its functioning defy much in the way of objective external measurement, and even the failure of a mouse's maze memorisation to materialise in the mind of the new home to its old cerebral folds does not exclude the possibility of other, more deeply set personality aspects being so transferred. Ultimately, the only true measurement of the success of such a procedure will be its performance on a human, and that human's response to the query: "Who are you, and how do you feel?"

Finding a donor:

Once the science of the transplantation is down, this will actually probably be the most difficult part. The typical organ donor has recently died in such a way that his body is not yet cold and the parts of interest are not very damaged, but the person as a whole is decidedly not alive. For this transplant, we need a live one. And one which is in relatively good shape (otherwise, why bother?), and one which is as close a match as possible to the brain-donor's chemical signature. Organ rejection in this circumstance would be most unpleasant. Awaiting the happenstance of a biological match falling into a vegetative coma is unlikely to be fruitful.

The optimal solution, about as science-fiction sounding as the idea of the transpant itself, is the generation of a clone of the donor. But there's one additional condition which ideally ought to be satisfied, which is that the surgery may be performed without committing outright murder.

One possible trick to that is to make an imperfect clone -- imperfect in the sense of it having only minimally developed brain functions under a big glob of unthinking fatty tissue where the contemplatory portions of the mind normally would sit, and so, being "brain dead" from the outset. This, still, may not sit well with a jury, so best to either have it legally cleared beforehand (however this may be accomplished), or evade the jurisdiction of any government which may take offense. And speaking of juries, that donor had best be prepared to provide for the care of his recipient body during a lengthy period of recovery, and take such steps as may be needed to prove by law that it is him, and entitled to exercise all rights of ownership, including property rights.

Nuts and bolts:

Amongst the most significant problems in the face of surgical success is the delicate state of nerves, which react poorly to being sliced apart and stitched together. As we've seen with hand transplants, re-innervation may be achieved, but thus far it is slow in coming and often stunted in final effect. To be most effective in maintaining maximal use of existing sensory organs, a brain transplant would probably require simultaneous transplantation of the most brain intensive of those organs: eyes, nose, ears, and tongue.

As for the rest of the nervous system, touch and feel and autonomous control of all those many muscles, progress has indeed been made on chemical and biological fixes to improve re-innervation. Hopefully if that donor is going into his own clone body, at least, the signals operating his fingers and toes and so forth won't get all crossed up. It may make sense for the donor to get himself cloned twice -- one to provide the full-grown body into which his good old brain may be deposited, the other to be kept in a fetal form so that it may be harvested for stem cells (I told you this might be workable, not that it would be pleasant and sqickless).

The most effective medium for the surgery would probably be complete immersion of both donor and recipient bodies in a closely fitting basin containing a clear oxygenated fluid made from the refinement of the donor's own blood plasma. A kind of tubing effect will need to be performed with the blood vessels going into the brain, with that vital organ being fully hooked into the new body's circulatory system before any work at all is done on integrating the nervous systems. So as to facilitate this, I've invented-- er, that is, it may be advisable to use a fully articulable double pallete for holding the bodies, old and new, so they may be positioned side by side, or head to head, and at any tilt or angle needed to minimise the threshold to be crossed for attachment of parts and systems.

The entire procedure may well be doable without causing too much disfigurement to the face, as everything ought to be accomplished by going in through the back of the head, through a semicircular cut to remove the back of each skull and expose the organof interest from behind. Obvious as it is that both bodies will need to be deeply, deeply sedated throughout, it bears mention, as well, that the amount of work being done on the head demands that a hole be cut in the throat of each body so that the breathing process may be made to bypass the mouth completely and instead be accomplished by the pumping of air directly into the lungs.

It is an open question as to just how much of the brain must be transplanted to preserve the donor's consciousness and memory in the recipient body, and just how much must be transplanted to insure full motor control. The inner estimate would allow the transferrence of no more than the bulk of grey matter. The outer estimate would include all parts of the brain and perhaps even the entire spinal cord as well.

Some other downsides:

Once a brain has been transplanted out of its old body, it almost certainly can't go back, so if something is wrong with the new one (which the recipient might not become "aware" of until the deed is done) they might find themselves stuck in a worse-off state. And, if something is wrong with the brain in the first place -- sufferance of Alzheimer's disease or Parkinson's disease or some other affliction settled in that organ -- a transplant won't really help things at all. These kinds of problems may accumulate; if you imagine immortality through constant re-potting of the brain in new bodies, best to think again, for all surgery has its risks, and every such operation will be a role of the dice, with those dice getting ricketier with each throw.

But still, if you're somewhere near the end of a long run, and you have time and wealth and optimism enough to afford to await the growth of your clone body, you may as well roll the dice on buying yourself another fifty years or so of life, and hope that by the time your second body has run its course, the technology exists to transplant your consciousness into a shiny immortal robot casing.

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