Identities

Neuronic events generate mental events. This has become a cliche but in fact is a very recent scientific discovery. Electrically firing neurons generate sensations which would not otherwise exist. Complicated electrochemical interactions between electrically firing neurons generate thoughts and personalities which would not otherwise exist.

(i) If person A's brain duplicated the interactions in person B's brain, then A would think that he was B, complete with B's memories, motivations etc. 

(ii) If an artificial neural network duplicated B's neuronic interactions, then that network would reproduce B's consciousness and sense of identity.

(iii) If some other technology exactly duplicated the effects of neuronic interactions, then that technology would generate self-conscious individuals maybe thinking that they were living on Earth in a particular historical period. 

(i) happens in Tim Power's The Anubis Gates. 

(ii) happens in Poul Anderson's Harvest Of Stars.

(iii) happens in Anderson's Genesis.

In The Anubis Gates, a character seeks immortality by repeatedly projecting his personality into someone else's body while at the same time displacing that person's personality into his own abandoned and soon-to-die body. 

The idea that personalities can be generated and duplicated in these ways links these three novels.