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My character have a split brain (severed connection between left and rigt hemispheres).

What is unique about his case is that not both hemispheres have the same identity any more.

From what I understood, each hemisphere is a brain of its own (mostly), this is evident from the patients who underwent Hemispherectomy and recovered to function almost normal.

His right hemisphere (doesn't control speech), now had so many different experiences because the researchers fed his left eye and ear different information for long time, which led to it having differeing identity.

Now the left hemisphere that control speech stopped covering up for the right side. And instead became aware of it, now the person can hold conversations with the different and judgy right hemisphere.

I have quite limited understanding of what identiy really means, and how do you actually "feel" a different identity in your own head, because you don't hear it, you just know these ideas is not yours, but the ideas are so structured it is like a conversation.

What problem this scenario will have that prevent this from working?

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    $\begingroup$ "Bicameralism [...] is a hypothesis in psychology that argues that the human mind once assumed a state in which cognitive functions were divided between one part of the brain which appears to be "speaking", and a second part which listens and obeys—a bicameral mind. The term was coined by Julian Jaynes, [...] in his 1976 book The Origin of Consciousness in the Breakdown of the Bicameral Mind, wherein he made the case that a bicameral mentality was the normal [...] state of the human mind as recently as 3000 years ago." (Wikipedia) $\endgroup$ – AlexP Jul 17 '17 at 16:20
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    $\begingroup$ I’ve seen that as the plot on a TV show a few years back — 3 lbs episode 2. $\endgroup$ – JDługosz Jul 17 '17 at 16:21
  • $\begingroup$ @JDługosz do you remember the show's name? $\endgroup$ – Aus Jul 17 '17 at 16:25
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    $\begingroup$ @aus I found it, and updated my comment. $\endgroup$ – JDługosz Jul 17 '17 at 17:02
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    $\begingroup$ @AlexP "The hypothesis is generally not accepted by mainstream psychologists." $\endgroup$ – Azuaron Jul 17 '17 at 17:04
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From what I understand[1], there's actually nothing wrong with this.

There has been research into what is known as "Split-Brain disorder", which has looked at patients who have undergone a hemispherectomy and ended up displaying some unusual behaviour.

It's worth noting that most hemispherectomy patients are actually fine post-surgery, with many regaining their full cognitive faculties shortly afterwards and returning to society with no long-lasting effects.

Having a split personality is a rare, but possible, outcome of having a split brain. The human function mainly affected by such surgery is actually language, so the fact that one side doesn't control speech, at least to begin with, is absolutely correct.

What you most likely end up with is the left half of the brain controlling the right half of the body, and vice versa. Over time, it is also possible for the two "identities" to become aware of the other and even to communicate, once Neuroplasticity has run its course and the two halves are on roughly equal footing as far as cognition is concerned.

It's quite likely that each half won't have full access to all their memories of the person they used to be before, and it's also possible that one side may even be completely emotionless to begin with, but as with everything else, with time they will each become what you or I would regard as a normal, fully functioning human, dual personality aside, due to plasticity.

In this particular case, there's a good chance that each side won't actually "feel" the other's presence any differently than they would "feel" the presence of any other person. There are plenty of people with multiple personalities (Dissociative Identity Disorder), and in some cases none of their personalities are aware of any of the others. When they switch, they may or may not retain memories of what they were doing beforehand, but if they do, they often believe it was that particular self that experienced them. They remember doing it, so who else could it be?

I can tell you, however, that if you are aware of an additional personality, it is entirely possible to have a conversation with them. You will often end up finishing each other's sentences, and you can tell what the other is feeling as they are "talking"(thinking) to you.

Ultimately, it varies enough from person to person that you can come up with just about any scenario, whether they know of each others' existence or not, whether they can converse or not, whether they can remember what the other experiences or not, etc. All these things are possible.

[1]: I took a Neuroscience module at University, so I should know what I'm talking about. Probably.

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    $\begingroup$ Just so we're clear, you can't have a split-brain when you have a hemispherectomy, because a hemispherectomy means that they removed a hemisphere of your brain. Split-brain can happen when they cut the corpus callosum (corpus callosotomy) because then the hemispheres can't speak to each other neurally. $\endgroup$ – Azuaron Jul 17 '17 at 17:08
  • $\begingroup$ A hemispherectomy does not necessarily mean that an entire half of your brain has been physically removed from your head. It can also mean that half has been disconnected or otherwise disabled, but left inside. $\endgroup$ – DisturbedNeo Jul 18 '17 at 8:43
  • $\begingroup$ What I was trying to say (poorly), is that a Corpus Callosotomy is a type of Hemispherectomy. $\endgroup$ – DisturbedNeo Jul 18 '17 at 10:53
  • $\begingroup$ A corpus callosotomy is not a hemispherectomy. What you're talking about is a functional hemispherectomy, where a hemisphere is completely disconnected. This includes, but is not limited to, a corpus callosotomy. With a functional hemispherectomy, the hemisphere is completely disconnected, but left in the cavity to prevent a buildup of cerebral spinal fluid. The other hemisphere then takes control over the entire body, so this still cannot result in split-brain. The functional removal of the hemisphere prevents it from communicating with any part of the body. $\endgroup$ – Azuaron Jul 18 '17 at 13:01
  • $\begingroup$ "The other hemisphere then takes control over the entire body"? Sorry, which of the two hemispheres is the "other" hemisphere? You're disconnecting the two halves and stopping them (mostly) communicating with each other, you're not disconnecting either half form the brain stem. There's nothing stopping either half from sending signals down the nerves to the arms and legs, hence why you can end up with each half controlling opposite sides of the body. $\endgroup$ – DisturbedNeo Jul 18 '17 at 13:57

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