I am no expert on sleep although my interest in consciousness has made me think very hard about the subject, because we all know what consciousness is in a certain sense, and this bears on what you mentioned before about going beyond the science proper. We all know what consciousness is. It's what you lose when you fall into a deep dreamless slumber and what you regain when you wake up. Well, that doesn't really help, does it, scientifically? But then the question is... what Crick used to call a scandal. To speak the way he did for a moment, in the name of his ghost... it's a scandal that we know so much about sleep and we haven't got the slightest idea what it's for. All right?

So, in fact, Gally and I – largely because there was an environment here of people like Ralph and his colleagues sort of working on sleep – we sort of thought, well, look, there are loads and loads of theories of sleep but none of them is particularly satisfying and maybe the one we're going to put together isn't either. But the idea was what we call the reapportionment theory of sleep – neural reapportionment: that when you're awake, it isn't so much a matter of your neurons getting tired, but they use up certain compounds like glutamate, which is a neurotransmitter at the synapses, in such a way that the cycle means that the glutamate has to first go through glia... glutamate and come back to neurons, not to the same place where it's released and when you look at that whole analysis, you see that the neurons that are the most active are the most impoverished in glutamate. That ain't so good. But if you fall asleep and you go into this slow-wave sleep where you just have this periodic stuff, then you tend to even up or reapportion the glutamate. We also extended the idea to certain structures responsible for energy called mitochondria which give rise to ATP – adenosine triphosphate, the fundamental energetic molecule – and we said, ‘What happens there is maybe the mitochondria move and you have to redistribute again’, and we put forth this general idea. Now, that was good for slow-wave sleep but I don't think we've really explained dream sleep, REM sleep, rapid eye movement paradoxical sleep, and it still remains a very great mystery. We know that it's about a third of our lives, isn't it, if you really add it up.

[Q] For humans, yes.

For humans. So then the question becomes, well, how far back does it go, which brings me to your area. And... well, then it becomes this question of fuzzy definition, doesn't it? You're going to get into the same problem you get with consciousness. You're going to find states that share certain properties of sleep, but how do you know it's sleep? And I guess the... the drosophila story is a very good example. They do show a lot of the properties of sleep, but you're not particularly going to become the drosophilas Freud, are you? Not going to look into dreams.