I asked the same question at Reddit here, but none of the responses were convincing.
So here's the thing: to the extent of what we know about consciousness, are end-stage Alzheimer's patients still conscious? I will use Christof Koch's attempt to define consciousness, as explained below.
What is the character of the NCC? Most popular has been the belief that consciousness arises as an emergent property of a very large collection of interacting neurons (for instance, Libet 1993). In this view, it would be foolish to locate consciousness at the level of individual neurons. An alternative hypothesis is that there are special sets of ``consciousness" neurons distributed throughout cortex and associated systems. Such neurons represent the ultimate neuronal correlate of consciousness, in the sense that the relevant activity of an appropriate subset of them is both necessary and sufficient to give rise to an appropriate conscious experience or percept (Crick and Koch 1998). Generating the appropriate activity in these neurons, for instance by suitable electrical stimulation during open skull surgery, would give rise to the specific percept.
So do end-stage Alzheimer's patients lose these types of "neurons"?