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Why do we sleep?
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Russell Foster studies sleep and its role in our lives, examining how our perception of light influences our sleep-wake rhythms.

Neuroscientist Russell Foster opens a session of TEDGlobal all about … us, asking the question: Why do we sleep? Thirty-six percent of our lives are spent asleep, which means, if you live to 90, you’ll have slept for 32 years. But we don’t appreciate sleep enough, says Foster. He quotes Thomas Edison — “Sleep is a criminal waste of time, inherited from our cave days” — and Margaret Thatcher — “Sleep is for wimps.” Simply put, says Foster, not only do we not appreciate sleep, but we treat it like an illness and an enemy.

Of course this simply shouldn’t be the case. In fact, some areas of the brain are more active during the sleep stage than while the body is awake. But the essential question that we — ahem — lose sleep over: Why do we sleep? There is no real consensus, but Foster gives three popular answers:

1. Sleep is for restoration, to replenish and repair metabolic processes. Indeed, a whole host of genes are “turned on” only during sleep — genes associated with restoration and metabolic pathways.
2. Sleep is for energy conservation, to save calories. This may seem an intuitive answer, says Foster, except that the difference between sleeping and quietly resting is about 110 calories a night, the equivalent of a hot dog bun. Not a very good upshot for such a complex process.
3. Finally, sleep is for brain processing and memory consolidation. This is the explanation Foster espouses. Studies show that if you prevent people from sleeping after a learning task, their ability to learn is basically smashed. And worse, our abilities to come up with novel solutions after a complex task are reduced after sleep deprivation.

The danger of sleep deprivation can’t be stressed enough. For one thing, sleep-deprived people fall asleep involuntarily, taking “microsleeps” they can’t control. Thirty-one percent of drivers, says Foster, will fall asleep while driving at least once in their lifetime. That is: 100,000 accidents a year happen because of tiredness. Läs mer >>

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Why you should listen to him:

Much as your ear does double duty (balance plus hearing), Russell Foster posits that the eye has two jobs: creating vision, but also -- as a completely separate function -- managing our perception of light and dark, providing the clues that our circadian rhythms need to regulate sleep-wake cycles. He and his team at the University of Oxford are exploring a third kind of photoreceptor in the eye: not a rod or a cone but a photosensitive retinal ganglion cell (pRGC) that detects light/dark and feeds that information to the circadian system. As Foster explains: "Embedded within our genes, and almost all life on Earth, are the instructions for a biological clock that marks the passage of approximately 24 hours." Light and dark help us synchronize this inner clock with the outside world. The research on light perception hits home as we age -- faced with fading vision, we also risk disrupted sleep cycles, which have very serious consequences, including lack of concentration, depression and cognitive decline. The more we learn about how our eyes and bodies create our sleep cycles, the more seriously we can begin to take sleep as a therapy.

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