What issues would need to be negotiated in advance before consenting to such a thing?

How would you firewall off the merge, but still benefit from it?

What would be appropriate termination conditions for a merge, considering that separating a long standing merge may leave all entities involved changed in discontinuous ways?

Interesting idea.

It reminds me a bit of how vague the contract for marriage is, and how you don't know what you get till you're in it, and even then it changes all the time.

I have uploaded a new version of the paper. Changelog:

• Edited abstract to emphasize the hypothetical nature of the paper a bit more. New version:

"We present a hypothetical process of mind coalescence, where artificial connections are created between two brains. This might simply allow for an improved form of communication. At the other extreme, it might merge two 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 from 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."

• Added a paragraph to the introduction section:

"The purpose of this paper is to introduce the concept of mind coalescence as a plausible future development, and to study some of its possible consequences. We also discuss the exocortex brain prosthetic as a viable uploading path. While similar concepts have previously been presented in science fiction, there seems to have been little serious discussion about whether or not they are real possibilities. We seek to establish mind coalescence and exocortexes as possible in principle, but we acknowledge that our argument glosses over many implementation details and empirical questions which need to be solved by experimental work. Attempting to address every possible problem and challenge would drown the reader in neuroscientific details, which we don’t believe to be a productive approach at this stage. Regardless, we believe that compared to some uploading proposals, such as using nanoprobes for correlational mapping of neuronal activity [Strout, 2007] or replacing neurons one by one [Moravec, 1988] our proposal, while still speculative, seems like a much more feasible development to occur in the near future."

• Clarified section 3. It now begins with the statement "Coalescence requires some technological means of connecting minds together. We consider three options: direct-brain-to-brain connections, an exocortex-mediated connection, and an option based on a destructive upload".

Correspondingly, "direct-brain-to-brain connections" is now section 3.1. Made several minor clarifying changes.

• Added mentions of sensory prostheses to section 3.1.:

"The technology exists today for creating hundreds of connections: e.g. Hochberg et al. [2006] used a 96-microelectrode array which allowed a human to control devices and a robotic hand by thought alone. Cochlear implants generally stimulate the auditory nerve with 16-22 electrodes, and allow the many recipients to understand speech in every day environments without needing visual cues [Peterson et al. 2010]. Various visual neuroprostheses are currently under development. Optic nerve stimulation has allowed subjects to recognize simple patterns and localize and discriminate objects. Retinal implants provide better results, but rely on existing residual cells in the retina. [Ong & da Cruz, 2011] Some cortical prostheses have also been recently implanted in subjects. [Normann et al. 2009] We are still likely to be below the threshold of coalescing minds by several orders of magnitude. Nevertheless, the question is merely one of scaling up and improving current techniques."

• Also edited section 3 to more clearly separate uploading-via-an-exocortex and mind-coalescence-via-an-exocortex. Among other things, added the following paragraph:

"Strictly speaking, an exocortex can act as merely an intermediate component that allows for mind coalescence, without necessarily leading to mind uploading. This might happen if the exocortex has insufficient capacity to house all the important parts of its user’s mind, or if it fails to take over subcortical functions necessary for the brain to operate. On the other hand, if a large part of a person’s brain functions have moved to the exocortex, he could be considered a partial upload even while many brain functions persist in the biological brain."

• Somewhat edited section 3 to clarify that when we talk about the biological brain not being capable of supporting two separate attentional/thought processes in the same medium, we refer to conscious attentional thought processes.

• Added a brief section 3.3., mind coalescence via full uploading:

"The third possible way to achieve mind coalescence is to first fully upload a human brain to a digital substrate somehow. Once this has been accomplished, connecting two or more brains to each other becomes straightforward. If the brains of Albert and Bob are both emulated in the same computer, then adding a connection between a neuron in Albert’s brain and a neuron in Bob’s brain might not have any essential difference from adding a connection between two neurons in Albert’s brain is. Full uploading can then be used to either implement a direct brain-to-brain connection, or to create a software exocortex to mediate the connection. However, we suspect that the technology for a physical exocortex will become available before the technology for full uploading will. As surveyed above, early brain prostheses in the form of cochlear implants and visual cortical implants already exist. Hippocampal brain prostheses have also been successfully tested in rats [Berger et al., 2011].

Most of the approaches for a full uploading that are currently considered viable also involve destructive uploading, i.e. cutting up the original brain to small slices and scanning them [Sandberg & Bostrom, 2008], which many people may feel uncomfortable with."

• In the "Barriers to Coalescence" section, moved "general integration difficulties" to be the first issue, and expanded on it:

"This is a catch-all category for various technical problems that might crop up. Human brains did not evolve for the purpose of being easily merged, and the process may prove harder than anticipated. Errors and mistakes may prove hazardous to the subjects, and it is currently unknown what kind of a merging process is needed to ensure that the resulting mind will remain sane and functional. As noted in the introduction, we are intentionally glossing over most of the implementation details, and much empirical work will be required before mind coalescence becomes a viable option."

• In the "lack of mutual trust and memetic hazards" section, changed "In considering whether to tell someone how to build a nuclear bomb," -> "In considering whether to reveal someone state secrets".

It is possible that single-attention-grabbing-thought lmitation is a limitation that can be overcome by learning (maybe this learning can be helped by temporary split-brain?). Some people claim to be able to partially overcome this limitation; it can be explained away as very fast switching, but as every thought has some background afterglow, very fast switching versus parallel thinking can be hard to distinguish.

I wonder what would happen in the end of merging of a temporary split - merging two minds can pass through a mostly-single-mind with two attention processes.