One Brain Enter. Two Brains Leave.

My question is inspired by this thread, at Eleusis’s recommendation (thanks Eleusis!)

In the linked thread, it’s discussed that some people who have been left with half a brain (such as from an accident) have been able to lead a mostly normal life, despite having only half the gray matter.

Now let’s assume for the sake of my question that brain transplants are possible. What would happen if we took one brain, split it in two, and put the other half in an otherwise healthy body, thereby making two people, each with half of the original brain.

Would there now be two variants of the original brain owner? Who would we identify as the original person? Any other hypothetical questions that should be asked and answered?

God, I really wish I knew the answer. I feel like I only have half a brain.

I have no clue, but if I had to wager a guess, I’d say that it would become two new different people. Or not.

This thread makes my head hurt. Great question though!

Well, I think the brain stem doesn’t work so well if you splice it in half. So if you cut a brain in half you’d get two dead people.

But if for the sake of argument there are two stems, and then half of the “higher brain” is transplanted…well, there might be some problems with rejection, but I’m not sure.

The brain is relatively unknown, in many ways. Would the person with the left half be really good at some things and the right half be good in others? Where do experiences and memories get stored? That’s a lot of what makes a “person” such as you deal with day to day.

Also, age makes a difference - it seems that the younger you are, the more able you are to have present brain tissue make up for the missing.

Short answer: I don’t know, but here are some more hypothetical issues.

The obvious sci-fi thing I’d hope for in my malicious, dirty mind is that we’d be left with one single person (personality) who posessed memories and life experiences from both “former people”…

Yeah, that would be freakin’ rad.

edit: spelling

In retrospect, I’d posit, with limited knowledge, that the end result would more like a lobotomy, with conflicting, unconnected hemispheres, each trying to control the body, and each taking over now or then.

I’m sure it’s not so simple.

We’ve discussed this before at great length and without any resolution. It’s the philosophical question of identity, upon which, my take is that the term ‘original’ is misleading. if you somehow contrive to acquire two identical copies of the same functioning human brain/mind, then you have two distinct people, both of whom consider themselves to be ‘the original’ that existed before, and both would be as right to say so as I would be in saying that I’m ‘the original’ me from yesterday.

Further reading:

Mangetout, with all due respect, I’m not sure you comprehend the OP here…

He’s saying take the left brain of you and combine it with the right brain of me.

Could we then become one with combined knowledge?
edit: grammar

One person would be good, and one evil. This requires that one of the bodies possess a goatee.

Or that each body possess half a goatee.

I’ve been looking for info on cephalopagus conjoined twins (fused at the skull, sharing large portions of brain), but from what I can tell they aren’t generally viable because the fused brains end up malformed.

While it’s not what you’re looking for, exactly, Abigail and Brittany Hensel are an example of two heads controlling one body. Despite the fact that each girl can only control and receive sensation from one half of the body, they manage to perform incredibly well at coordinated activities like typing and sports. They even have their driver’s licenses - one girl controls the pedals and one controls signaling.

The split-brain-transplant you’re suggesting in the OP would necessarily result in a half-and-half body, sort of like what the twins are living with. Without having developed like that and adapting since birth, though, I’m not sure how that hybrid person would manage to function.

Actually, I think it might be you that fails to comprehend it; to me, it reads as if we’re inserting a functioning half-brain into each of two empty bodies - there’s no mention of half an existing brain in the recipient bodies.

In right-handed males, the left hemisphere controls language, so we’d probably unfairly call that the original person, that being the one we could talk to.

A variation of this experiment has actually been done. In rare cases of intractable epilepsy, surgeons have gone in and cut the corpus callosum, the main nerve tract connecting the right and left sides of the brain. The original thought was that a seizure would start in one hemisphere and not be able to spread to the other side, and hey, half a functioning brain’s better than none. For some reason, though, it stopped seizures in both sides. Anyway, something else that happened is that each hemisphere developed it’s own personality. Mr Split-Brain might go to a party and his left hemisphere would politely chat up a woman, but his left hand, controlled by the right hemisphere, would pinch her on the butt, much to the left hemisphere’s embarrassment.

There are philosophical papers being written about these questions, and pretty much every position you can think of is defended by some thinker or other.

My own view is that each post-op person is the same person as the pre-op person, but they are not the same person as each other. This means “the same person” is not really an identity relation.

Things get complicated though, because you have to ask, who owns the person’s house? Who is he or she married to? And so on. Well, actually I think these problems are soluble. Just split it down the middle. Ideally, each person should have a “will” of sorts specifying how the split should be done in the event of his division. This way both post-op people will be equally happy and willing in recieving their share. But if someone doesn’t have a will, things will be messy, but that’s just how it is when people who need wills don’t have wills in real life.


Do you have a citation for that last bit?

It was my understanding that in normal conditions, split-brain people behave indistinguishably from non-split people. To get the weirdness, you have to somehow isolate the perceptions of one brain-halffrom the perceptions of the other, using walls dividing up the field of vision or something.


You’re right - the oddness really showed up when the left and right halves of the brain were stimulated individually, by showing a word or item to one half of the field of vision. Sperry was, I think, one of the first to do work on split-brain patients, and the results were really neat. Because the connection between the hemispheres is cut, they can’t communicate, but each half can still do its own thing. Gazzaniga took things a little further, doing more work that showed how the brain will compensate for a lack of information, and how the verbal side will make stuff up to explain things it doesn’t understand.

Apologies for the horrible style of the websites, but the info is good.

No, you’d have one dead person, and one 1820s-style “Frankenstein” abortion.

Given your screen name I am completely surprised you didn’t mention the Bruce
Campbell vehicle The Man With A Screaming Brain.

Oh the horrible shame. I must have another Evil Dead marathon to regain my honor!

I remember reading in college specifically about the butt-pinching incident but don’t remember where.



Strange that I hadn’t heard about that before.