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Why do humans need to sleep?

Why do humans need to sleep?
Mark from Stoke on Trent (age 25-34)

Why do humans have to sleep and will we be able to eliminate the need for sleep?
Katie Edwards from Greater London (age 25-34)

Why do we need sleep and what is it?
Rebecca James from County Durham (age: 5-14)

Why do you get sleepy???
Laura Gale from Swansea (age 5-14)


Most sleep researchers are agreed that sleep provides recovery, but what exactly is recovered is another matter. Unfortunately, we haven’t the technology harmlessly to get inside living cells of the sleeping animal, especially neurones or glial cells within the human cortex, where we know sleep is of particular importance. Besides, sleep must have several functions, evolved to suit the circumstances of various animals, and probably not the same for humans and mice, for example. For the mouse, sleep stops it running about aimlessly and conserves much energy by confining it to the insulation of its nest where it can huddle against other mice. It can’t sit still and relax in wakefulness as this entails thinking, watching, reading etc – behaviours obviously beyond the repertoire of its simple cortex. We humans can easily do this, and so sleep is not necessary for our energy conservation. If, instead of sleeping over-night, we lie awake but relaxed, the extra energy needed is only the equivalent of eating an extra slice of bread – hardly worthwhile. On the other hand, our large and complex cortex requires sleep rather than relaxed wakefulness for its recovery, whereas the mouse’s simpler cortex probably needs little sleep in this respect. Although a rat will die after about two weeks of total sleep loss, this is a remarkably long time in proportion to its life-span of two years. Its death through sleep loss has something to do with its failure to conserve body heat – but no body organ seems to fail, including its brain.

Jim Horne, Professor of Psychophysiology and Director of the Sleep Research Centre at the University of Loughborough


One Response

  1. Biologists and neuroscientists take a different view of sleep from psychologists, and predominantly agree that consolidation of memory is its major function. Rats and mice that learn a task like finding the way through a maze do not remember it so well if they are deprived of sleep soon after the training session. And after being given a new experience, they sleep more in the next three hours than their cage-mates who had no such experience. Similar evidence exists in humans: memory consolidation resulting from sleep has been shown in the learning of verbal lists and in gaining visual and motor skills. The theory that sleep’s purpose is to conserve energy, keep animals warm or out of harm’s way is not accepted by most biologists. Evolution has produced such amazing adaptations that it is inconceivable that animals cannot keep still without having the handicap of being unable to see, hear or feel any but quite intense stimuli. There must be some brain process going on during sleep that needs sensory input to be excluded. This is probably the replaying of the day’s experiences in the brain so as to integrate them with the existing body of knowledge, and consolidate them. Sensory experience during this process might result in current events being wrongly classified in the brain, perhaps getting mixed up with the otherwise orderly reorganisation of previous memories with novel related experiences. The replay of memory during sleep might explain dreaming – but that is much harder to prove.

    Director of Learning and Teaching

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