Deep sleep is associated with slow brain waves, and larks spent 50% more time in such slow-wave sleep than owls did.

睡眠之深与否与慢波有关，而百灵鸟型处于慢波睡眠的时间比夜猫子型多50%甚至更多。

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Particularly important is "slow-wave sleep," a period of very deep sleep that comes earlier than better-known REM sleep, or dreaming time.

尤为重要的是“慢波睡眠”，一段非常深刻的睡眠来更好地早于著名的REM睡眠，或做梦时间。

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Their study shows that as young people grow older they spend less of their sleeping time in slow wave or deep sleep.

BBC: Sleep linked to ageing