We present a hypothetical process of mind coalescence, where articial connections are created between two or more brains. This might simply allow for an improved form of communication. At the other extreme, it might merge the minds into one in a process that can be thought of as a reverse split-brain operation. We propose that one way mind coalescence might happen is via an exocortex, a prosthetic extension of the biological brain which integrates with the brain as seamlessly as parts of the biological brain integrate with each other. An exocortex may also prove to be the easiest route for mind uploading, as a person's personality gradually moves away from the aging biological brain and onto the exocortex. Memories might also be copied and shared even without minds being permanently merged. Over time, the borders of personal identity may become loose or even unnecessary.