Harry currently thinks that Atlantis is some form of system that locks onto human bodies with the Blood Of Atlantis gene and detects their commands (spells, odd potion-making actions, etc).

A simple explanation for Horcrux is that it is basically a form of uploading. Although that would make it seem overly simple for Sufficiently Creative Harry to find a way to make horcruxes without human sacrifice.

Alternatively, a wizard's soul has read-only access to their brain.