REM
Several times a night we enter a phase of sleep termed Rapid Eye Movement (REM). Observing a person during REM sleep shows their eyes to be moving vigorously under the eyelids. If they are woken up in the middle of it, the sleeper will report having been in the middle of a dream. As many dreams are composed of the previous day's events, some scientists argue that this provides evidence that the brain needs sleep to process what we experience during waking hours, and store the events as memories. Whatever role REM sleep has in adults it is most prevalent in the developing foetus, leading some to suggest that its dreams act as a cinema: the brain is kept active to stop it becoming bored, either during sleep or with the relative lack of external stimulation within the uterus. Try proving that one.

Sleep Inertia
That's the scientific name for the grogginess felt after waking. One to five minutes of lethargy is usual, and performance may be reduced for about twenty minutes. However it can persist long enough in some people for it to be a real problem. Rory, the apprentice at the garage where I used to work, seemed to have sleep inertia lasting all day...

'Power Naps'
There is good scientific evidence that napping is effective in improving performance and reducing sleepiness, especially if they are taken before long periods of work to protect against feeling tired, rather than when already feeling sleepy. It has been proven that the benefits of a 25 minute nap may be felt for hours afterwards, so the fact that I wasn't allowed to doze for even one second, (unlike the competitors in the reality TV programme 'Shattered', who were allowed 'power naps') goes some way to explain why I found it so difficult to stay awake for the seventy hours.

The Body Clock
Light or dark, we still get tired at the appropriate time: there must be an inner clock telling us when to sleep. The clock appears to be hormonal. Many hormones show cyclical changes in concentration during the course of twenty four hours, but the key hormone seems to be melatonin. Its concentration rises in the evening, which makes us feel sleepy; in fact one can take synthetic melatonin as a sleeping tablet. In the morning the concentration falls, helped by light. When the eyes receive strong light (not artificial lighting) melatonin production is depressed via links with the visual system. This effect 'locks us in' to the natural twenty four hour day.

There have been experiments performed where people have been cut off from knowledge of the true passage of time, and denied access to daylight - in one case this was done in a pot-hole. The people still showed a cycle in the hormone levels, but without the daylight to keep it in time, most people's clocks run slow - say a twenty five hour cycle. Consequently, the cave-dwellers gradually got out of step with their friends on the surface, doing everything later and later.

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Content last updated: 25/08/2005

Dr. Pater Naish

Peter Naish is a lecturer in Cognitive Psychology at the Open University. He has a particular interest in the mechanisms and effects of hypnosis, including its ability to influence perceptions or memories.

He is a member of the Council of the British Society of Experimental and Clinical Hypnosis, and chairs the Scientific Advisory Board of the British False Memory Society.

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