Tuesday 27 August 2002

Pic of the day: Naps are effective because they tend to happen when we are really sleepy, and therefore take us straight to the right sleep type.

Sleep

Things didn't go too badly. I fell asleep a few times at work, but not for long. And I managed to stay awake through the evening too.

***

I reflected on the strange fact that sleep is such an irresistible desire. It is right up there with water and before food, at least unless you are really really starving. It is harder to go two days and nights without sleep than without food, not that I would volunteer for any of them. But why is this so? We intuitively understand our desire for food and drink, but the need for sleep seems a mystery.

Actually I know of two different reasons for sleep. The deep sleep ("delta sleep") is for rest and regeneration for body and brain. And the dream sleep ("R. E. M. sleep") seems to be important for learning and for unlearning; it is proven to be essential for our sanity. But these two sleep phases don't even fill half our sleeping time. Our sleep is padded with at least two other distinct phases, three if you consider the process of falling asleep. And this pattern is hardwired into our brain. After a period of serious sleep deprivation, we spend much more of our sleep in the two essential sleep phases. But already the next night we revert to the normal pattern.

My best guess is that our sleep is padded out to fill most of the hours of darkness. As highly visual creatures adapted for daylight, running around in the dark is simply too dangerous for us. We could fall off a cliff or into a river; but just as bad, we might get separated from our tribe. Better to suffer the inconvenience of forced passivity for eight hours each night.

The cycle of sleep phases takes ca 90 minutes, from deep sleep through drifting images and "thoughts" to dream sleep and back. The same cycle goes on in the background during the day. Sometimes it will break through and cause intense daydreams (R.E.M. phase) or intense tiredness. Naps are surprisingly effective, but if we nap too comfortably we may go on to the less efficient sleep phases and waste time.

These days electric light has reduced the difference between day and night. And so sleep doesn't work quite the way it used to. Some people sleep too little, others sleep at the wrong time. But we all sleep, and we all need to sleep. And it is surprisingly hard to resist. Speaking of which, in my case, like now.