This could be due to the effects of our natural sleep-wake cycle, or circadian rhythm, the researchers suggest.

研究者表明，这是由于我们的自然睡眠-觉醒周期或者昼夜节律的影响。

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Get active outdoors between 6:30 and 8:30 a.m.; it's the prime window to wake your body with sunlight, kicking off a healthy sleep-wake cycle.

早上6：30——8：30进行活跃的户外运动；这是通过阳光唤醒你身体，开启健康的醒睡周期的主要窗口。

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In one study, about half of school pupils were able to shift their daily sleep-wake schedules by one hour.But significant change can be a challenge.

一项研究表明，大约一半的小学生可以调整他们每天的睡觉起床时间一小时，但更大的改变会成为一个挑战。

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And then you do twenty-plus miles the next day,you sleep in a tent, you gotta wake up and you got to do it again.

VOA: special.2009.11.02

Impairment in the body's internal clock, ultimately disrupting a person's sleep-wake cycle, is just one of the potential symptoms of dementia.

CNN: Building relationships amid memory loss

In another experiment the researchers wake up sleeping mice by sending a light signal to the hypothalamus, the brain's controller of sleep-wake cycles.

FORBES: Magazine Article

Melatonin products are usually synthetic versions of the hormone made naturally by the pineal gland, in the brain, which helps regulate the body's sleep-wake cycle.

CNN: Should your teen take melatonin for help with sleep?