Photo: James Duncan Davidson

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.

Photo: James Duncan Davidson

For those who want to take control of their sleep habits, Foster has some tips:

1. Decrease your amount of light exposure at least half an hour before you go to bed.
2. Make your room a bedroom a haven for sleep by making it dark and cool.
3. Turn off your mobile phones, computers and anything that will excite the brain.
4. Don’t drink caffeine after lunch.
5. Increase light exposure when you wake up.

He also busts some myths:

1. Teenagers are lazy? Nope. Their biological clocks make them sleep and wake later.
2. You need 8 hours of sleep a day? Nope. That’s just an average.
3. Older people need less sleep? Nope. Sleep demands of the age don’t slow down.
4. Early to bed, early to rise makes a man healthy, wealthy and wise. Nope. Just wrong, on many levels. It just makes you more smug.

Good to know. But where Foster’s true expertise comes in is in new research he and his colleagues are conducting on the links between sleep and mental illness. According to Foster’s research, genes that have been shown to be important in the generation of sleep, when muted, predispose individuals to mental-health problems. Foster suggests that sleep levels could be used as an early warning signals for illnesses like schizophrenia. Research has found that schizophrenia patients stay awake during the night phase, asleep during day, suggesting that sleep and mental illness aren’t simply associated, they are physically linked. Which opens the door for sleep to be used as a new therapeutic target.

To conclude, Foster urges us to take sleep seriously. He gives a final quote on sleep, from the writer Jim Butcher: “Sleep is God. Go worship.”

Russel Foster’s talk is now available for viewing. Watch it on TED.com »