Nobody knows exactly how or why the body is able to do this, but researchers say that our biological clocks, which keep track of time, have something to do with it.
Just above the optic nerve in the brain is a master clock called the suprachiasmatic nucleus, said Dr Ravi Allada, a neurobiologist who specialises in sleep and circadian rhythms at Northwestern University.
This clock synchronises and coordinates our body’s circadian rhythms, which help us prepare for things that happen at various times of day — such as falling asleep at night and waking up in the morning.
One way our body does this is by sensing the levels of light around us, Foster said. Special cells in our eyes detect changing light levels, such as right before and at dawn — even through our eyelids when our eyes are closed, he said. These cells probably don’t tell our bodies precisely what time it is, but they may communicate that we’re approaching the time we normally get up.
This triggers changes — such as increases in the hormones cortisol and adrenocorticotropin, as well as in blood pressure, Foster said — that help us prepare for activity.
What about the times you’ve woken up right before your alarm when you’ve had to be up much earlier than your body is used to, such as to catch a flight or attend an important appointment?
Instead of waking up based on what time it is, Allada said, our bodies may be waking up based on how much time has passed since we went to bed — working almost like an hourglass. If we go to bed knowing we must be up in 4 hours, something may help to ensure that we wake up after 4 hours.
When things go awry
If our bodies are so good at sensing the time, why don’t we always wake up just before our alarm? And why is it that some people never wake up before their alarm?
Foster isn’t sure. It’s possible that when you’re especially tired, your body’s need for sleep overrides its biological clock, he said.
Or sometimes, if you feel nervous about waking up on time, stress may cause you to wake up earlier than you’d like, Allada said.
The bottom line
There are still far more questions than answers about why and how our bodies sometimes wake us up before our alarms.
But to maximize the chance that you’ll rouse on time on your own, Foster said, it can be helpful to set your alarm for the same time each day so that your body gets used to waking up at a regular time.
This article originally appeared in The New York Times.
Written by: Melinda Wenner Moyer
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