One popular thought experiment, usually to explore the possibilities of functionalism, is to replace one neuron with a “functionally equivalent” silicon part and note that it wouldn’t change phenomenal experience. So the question then is, if you keep doing that, and replace all neurons with silicon, what happens?
The possibilities seem to be, you, phenomenally in every way remain the same, a zombie, or a “Sixth Day” you. Let’s take another spin on this thought experiment. What about replacing all neurons with exact physical replica neurons?* Is it still you? Does it matter how fast these neurons are replaced? What if neurons are replaced one by one sequentially, a real neuron is killed, and another one replaced, within a matter of seconds? What about two neurons at a time? A hundred? What about destroying all of them and replacing them within planck time constraints? What about everything in the last sentence, plus re-materializing ten feet away?
If we think that wouldn’t make a difference, then it should be the case that an atom for atom exact replica of you could be created and you’d have two phenomenal experiences simultaneously. If that’s absurd, then it seems YOU are tied to your specific neurons. There might be some. or a lot of truth to the folk wisdom that neuron longevity and development constancy plays a part in continuity of experience. It might be that over the course of many years, depending on what neuroscience discovers, that you are your own Sixth-Day you.
*I’m ignoring quantum interpretations of consciousness. Physicists can inform better here, but I believe there are entanglement issues which might hold an impossibly high standard to making true exact replicas.