I think it’s pretty common to think of how asleep someone is as something that comes in degrees, by which I mean that someone can be a little bit asleep (in which case their eyes will be closed, but they might remember overhearing a conversation nearby, and be wake-able with very little stimulus, such as someone whispering their name, or opening the door of the room they are in), or very very deeply asleep, in which case they might sleep through a loud storm/band playing next door/someone poking them or even moving them, and in all kinds of states in between. But Demmett and Vaughan’s The Promise of Sleep argues that this is wrong: though there are indeed different kinds of sleep (i.e. stages 1-4 and REM sleep) sleep itself is discrete on/off thing.

The main experiment Demmett cites in support of this goes more or less like this: you keep a subject awake for 3 or 4 days, so that they build up a large sleep debt, making them liable to fall asleep quickly. Then you clip their eyelids open (yes, it does sound torturous) and sit them in front of a bright flash, like that of a camera, which goes of randomly, but on average every 8 seconds or so. Then you ask them to push a button every time the flash goes off. Here’s what happens. For the first couple of minutes they push the button diligently every time the flash goes off. But after a couple of minutes, there is a flash and they fail to push the button. The experimenters ask them why they didn’t push the button, and the subject replies that there was no flash. But of course, there was a flash, the experimenters all saw it, and the subject is sitting there with their eyes pinned open in front of the flash bulb. The electrodes attached to the subject’s scalp (which you can use to measure electrical activity in the brain) show that the subject actually fell asleep for 2 seconds.

Demmett argues that sleep is total cut-off of normal perceptual processes: basically the brain drops a wall between the subject and the outside world, such that the sleeper simply doesn’t perceive the outside world at all. The difference between sleep and unconsciousness, coma or death is that certain things can prompt the removal of the wall (sounds, shaking the sleeper, etc). But still, either the wall is there or it isn’t—the subject is either asleep or he isn’t—and if he’s capable of paying attention to anything in the outer world (groggily attending to nearby conversations, for example, or some language learning tape) then he isn’t asleep at all.All of which makes sleep seem really strange.

It’s clear from the book that nearly everything we know about sleep has been discovered very recently, and that a lot of falsehoods about sleep are still very widespread. Some of the new data about sleep has been achieved-unsurprisingly enough-through new ways of studying the brain, but there’s also been plenty discovered that could have been discovered much earlier if only someone had looked. In fact, it’s completely amazing, and in need of explanation, that no-one every noticed these things before. For example, Rapid Eye Movement (REM) during sleep is strikingly obvious to anyone who’d care to look. And it is ubiquitous: everyone – babies, old people, animals, men, women – has hours of REM sleep every night (well, in the case of nocturnal animals, it might be during the day, and hibernation and the like turn out to be special cases. And it takes a few weeks before the sleep of babies is consolidated into longish alternating periods of wake and sleep..but you get the point – REM sleep is all over the place.) And it isn’t as if no-one ever watched anyone else sleep. And yet pre-20th century theories of sleep (Aristotle apparently thought vapours arising from one’s stomach after eating put one to sleep) make no mention of it, and it wasn’t discovered and studied until a few years ago. Why?Is it just that people assumed sleep was uninteresting?

It seems to me that there are a bunch of issues that could be of interest to philosophers here, but the only philosophy of sleep book I’ve found on Amazon is Robert Macnish’s The Philosophy Of Sleep, which is a 2006 reprint of the 1830 book. Here’s his description of waking from a healthy night’s sleep:

The sleep of health is full of tranquility. In such a state we remain for hours at a time in unbroken repose, nature banqueting on its sweets, renewing its lost energies, and laying in a fresh store for the succeeding day. This accomplished, the slumber vanishes like a vapour before the rising sun; languor has been succeeded by strength; and all the faculties, mental and corporeal, are recruited. In this delightful state, man assimilates most with that in which Adam sprang from his creator’s hands, fresh, buoyant and vigourous; rejoicing as a racer to run his course, with all its appetencies of enjoyment on the edge, and all his feelings and faculties prepared for exertion. (2) 

So, no need for coffee then! And no beta-waves. There is some mention of eye movement in the index, so I’m going to order a copy of the book (I got this stuff from the Amazon “search inside” feature) and see if there’s anything that could be construed as early observation of REM. There might be a few more posts about sleep in the next few days or so.