Many science fiction stories feature the concepts of mind uploading and consciousness transfer. Let's assume that the personalities of the two people in one mind function sort of like dissociative identity disorder where the personalities remain distinct and separate instead of merging into one, and usually only one is dominant at a time. I am curious:
- Assuming it is possible to upload a person's consciousness and then download/transfer a consciousness into another biological brain, how many simultaneous consciousnesses (along with memories) could one brain hold?
- Is it even possible to remember two distinct lifetimes of knowledge?
- Would a brain's information alone represent the whole of a person, or would information from other body systems (e.g. the entire nervous system) be needed as well?
- In a mind with two consciousnesses, could one consciousness be selectively taken out, possibly to transfer into another host, leaving both minds distinct once again? Or would there always be a trace of the other in each mind?
SPOILER ALERT: For the sake of an (imperfect) example, I think one of the most popular is the Katra transfer from Spock to McCoy in the 2nd and 3rd Star Trek films. McCoy struggles with having the consciousness of Spock transferred into his mind, driving him a little mad, until he can re-transfer it back into Spock's body in the fal-tor-pan ceremony. Spock never "takes over" but it's clear that his katra is influencing McCoy, and all of Spock's mind and memories are contained within McCoy until they're released. This is an imperfect example because Spock's personality isn't really apparent within the body of McCoy, because the method of katra transfer is vague, and because McCoy and Spock are two different species.
Please don't assume when answering that it has to take place in the Star Trek universe! I just felt an example of the general concept may help.