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:

  1. 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?
  2. Is it even possible to remember two distinct lifetimes of knowledge?
  3. 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?
  4. 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.

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    $\begingroup$ I see two issues with your question: first, you are asking details on a fictional technology, which being fictional can be adapted to each and every fiction; second, there are too many questions. $\endgroup$
    – L.Dutch
    Nov 15, 2017 at 11:09
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    $\begingroup$ hm I'd say about a brain can hold approximately ...two and a half brains? $\endgroup$
    – Fl.pf.
    Nov 15, 2017 at 11:24

1 Answer 1


The brain is not one big module with a single task. It's a big cluster of semi-interdependent modules each working on their own - and sometimes conflicting with one another (e.g. mental disorders). (for reference: Robert Kurzban's "Why everyone (else) is a hypocrite")

This structure implies that the mind and personality are not as simple concepts as you might think. You can not easily define what makes a person or a personality. And you can not transfer that from one person to another person without entirely rewiring the "host" brain. You also can't transfer modules as the connections of modules need to work in specific ways with other modules - maybe the other brain doesn't have these.

A brain only consists of structures it needs. There is no "free space" to be taken by something else. You can't just cram more stuff in there. Especially not twice as much - like transferring another personality in there.

The basic premise of your question is contradicting science. Therefore no one can give you any scientificly valid answers to your question. If you want to write about that, you can make up something fictional.


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