So, using my spooky psychic powers1, I have observed that I have been cited a few times here and there in the ongoing argument between those of us who adhere to pattern identity theory and those of us who adhere to continuity identity theory, with particular reference to the so-called “sleep argument”; i.e., that interruptions in consciousness can’t cause a break in identity because we sleep, which interrupts our narrative thread of consciousness.
Except, argue they, it doesn’t. Which we could argue and I’d be prepared to argue: we certainly have some type of consciousness going on in REM sleep, but it gets a lot more dubious in deeper sleep states than that.
But in any case, and here’s my point: it doesn’t matter, because sleep is only the least of the interruptions in consciousness which can be examined. There are also unconsciousness, anaesthesia, coma (natural), coma (medically induced), various states of suppressed brain activity using TMR, extreme hypothermia simulating brain death, and seizure disorders which may not suppress all electrical activity in the brain, but do derange it all to hell. (In animals – sadly not in humans, due to our scientists being bound by petty morality – we have cooled mammals to sub-freezing temperatures with no brain activity, even, and revived them.)
In short: people have come back from having a null electroencephalogram, which is to say a complete absence of consciousness and indeed dynamic mind-state. (Which is why checking for brain death in a medical context requires a sustained absence of such, not just noticing said absence is present.)
All of which is to say, folks, if you’re going to argue continuity of consciousness, it’s not the “sleep metaphor” that you have to dismiss – it’s the curious ability of the brain to reboot itself from a total lack of activity into someone who is functionally identical to the person whose brain was shut all the way down. (Or, y’know, advance the argument that a large number of coma patients, etc., are in fact completely different people to the ones who went under in the first place, if you want to retain argumentative coherency.)
Incidentally, for a more coherent continuity identity theory than continuity of consciousness, you could always consider causal continuity – in which you remain you through time because your mind-state is necessarily causally derived from your previous mind-state, which has the advantage over consciousness continuity that it doesn’t have the aforementioned problem with neuroscience kicking it repeatedly in the head, belike.
…it does, however, tend to produce results isomorphic with pattern identity in the cases where the difference is relevant, inasmuch as if you copy your mind-state, both copies have causal continuity in this sense from your previous mind-state. (The chief difference here is that two identical mind-states which evolved independently would not be considered the same person, although since that is unlikely to happen even once in the entire lifespan of the universe, it’s not really much of a problem.)
It also makes it a little more explicit that separating diverged copies into two people when they no longer wish to be – or obviously aren’t any more – the same person is much more of a legal issue than one with a convenient cog-sci answer.
1. Referrer logs.