Let's assume one neuron is replaced every second. No problem, nice and gradual. What if it's one every millisecond, every picosecond? Should make no difference,

Let's assume one neuron is replaced every second. No problem, nice and gradual. What if it's one every millisecond, every picosecond? Should make no difference, because it's still one by one. It should make a difference how long it takes, though. Assume that consciousness is a physical process. If new neurons take part in this process after the old ones die (so that we have continuity as part of normal "healing"), there must be some time scale over which those neurons become an effective part of the consciousness process. At minimum, if consciousness is a "network effect", this would be on the order of the latency of inter-neuronal communications. If the cells are doing some processing which forms part of consciousness, the time scale would increase. To throw out some wild numbers: neuronal latency seems to vary, but I found a number for visual-cortical neurons of about 80 ms. (http://redwood.berkeley.edu/bruno/npb261b/whitney-reading/krekelberg.pdf http://redwood.berkeley.edu/bruno/npb261b/whitney-reading/kr...) And you can't replace more than a few cells at a time (I wonder what fraction?) if you want to avoid impairing consciousness during the process. (This also doesn't include whatever the time is to make an effective copy of a given neuron and it's state; we're assuming instant perfect copying.)