Maybe this also happens to you sometimes:
You go to bed with a morning obligation in mind, perhaps a flight to catch or an important meeting. The next morning, you wake up alone to find you’ve beaten your alarm clock by a minute or two.
What is happening here? Is it pure coincidence? Or maybe you possess a supernatural ability to wake up precisely on time without help?
It turns out that many people have come to see Dr. Robert Stickgold over the years with questions about this phenomenon.
“It’s one of those questions in the study of sleep where everyone in the field seems to agree that what’s obviously true can’t be true,” says Stickgold, a cognitive neuroscientist at Harvard Medical School and Beth Israel Deaconess Medical Center.
Stickgold even remembers telling his mentor about it when he was just starting out in the field – only to be greeted with a dubious look and a less than satisfactory explanation. “I can assure you that all of us sleep researchers say ‘bullshit, that’s impossible,'” he says.
And yet Stickgold still believes in it is something to that. “This type of precision alarm clock is reported by hundreds and thousands of people,” he says, including himself. “I can wake up at 7:59 a.m. and turn off the alarm clock before my wife wakes up.” At least, sometimes.
Of course, it’s well known that humans have an elegant and complex system of internal processes that help our bodies keep time. Shaped somewhat by our exposure to sunlight, caffeine, meals, exercise, and other factors, these processes regulate our circadian rhythms throughout the roughly 24-hour cycle of day and night, and it affects when we go to bed and wake up.
If you get enough sleep and your lifestyle is aligned with your circadian rhythms, you should generally wake up at around the same time each morning, adjusting for seasonal differences, says University sleep scientist Philip Gehrman. of Pennsylvania.
But that still doesn’t sufficiently explain this phenomenon of waking up precisely a few minutes before you wake up, especially when it’s a time that deviates from your normal schedule.
“I hear that all the time,” he says. “I think it’s that anxiety of being late that contributes to it.”
Scientists are getting curious – with mixed results
In fact, some scientists have tackled this conundrum over the years, with admittedly mixed results.
For example, a small 15-person study from 1979 found that over two nights, subjects were able to wake up within 20 minutes of the target more than half the time. The two subjects who did best were then followed for another week, but their accuracy quickly dropped. Another small experiment let participants choose when they would get up and found that about half of spontaneous awakenings occurred within seven minutes of the choice they wrote down before falling asleep.
Other researchers have taken more subjective approaches, asking people to report whether they have the ability to wake up at a certain time. In one such study, more than half of respondents said they could do it. Indeed, Stickgold says it’s entirely possible that “like many things we think we do all the time, we only do it once in a while”.
OK, so the scientific evidence isn’t really overwhelming.
But there was one intriguing source of evidence that caught my eye, thanks to Dr. Phyllis Zee, chief of sleep medicine at Northwestern University Feinberg School of Medicine.
Stress hormones may play a role
In the late 1990s, a group of researchers in Germany wanted to understand how expecting to wake up influenced what is called the HPA axis – a complex system in the body that processes our response to stress and involves the hypothalamus, pituitary gland and adrenal glands.
Jan Born, one of the study’s authors, says they knew that levels of a hormone stored in the pituitary gland called ACTH begin to rise before the time you usually wake up, which to his tower signals the adrenal glands to release cortisol, a so-called “stress hormone” that helps wake you up, among other things.
“In this context, we decided to try it and it actually turned out as a hypothesis,” says Born, who is now a professor of behavioral neuroscience at the University of Tubingen, Germany.
Here’s what Born and his team did: They found 15 people who normally woke up around 7 or 7:30 a.m., put them in a sleep lab, and took blood samples over three nights.
The subjects were divided into three different groups: five of them were told that they had to get up at 6 am; others were assigned at 9 a.m.; the third group received a wake-up call at 9 a.m., but were then unexpectedly woken up at 6 a.m.
Born says a distinct difference appeared as their wake-up time approached.
Subjects who planned to wake up at 6 a.m. had a noticeable increase in ACTH concentration, beginning at about 5 a.m. It was like their body knew they needed to get up earlier, Born says.
“It’s a good adaptive preparatory response from the body,” Born says with a chuckle, “because then you have enough energy to get up and you can do that until you have your first coffee. “
This same increase in stress hormones before waking up was not recorded in group members who hadn’t planned to get up early, but were surprised by a 6 a.m. wake-up call. The third group – the one assigned a 9 a.m. wake-up time, had no pronounced rise in ACTH an hour before getting up (Born says this suggests it was just too late in the morning to see the same effect.)
Born’s experiment didn’t actually measure whether people would end up waking up on their own before a predetermined time, but he says the results raise some intriguing questions about this phenomenon. After all, how did their bodies know they should get up earlier than usual?
“It tells you that the system is plastic, it can adapt, in itself, to time lags”, he specifies. And it also suggests that we have some ability to operate this “system” while awake. This idea is not entirely foreign to the field of sleep research, he says.
A “scientific mystery” yet to be solved
“It’s well known that there’s some sort of mechanism in the brain that you can voluntarily use to influence your body, your brain, while it sleeps,” Born says. He points to research showing that hypnotic suggestion can help put someone to sleep more soundly.
Northwestern’s Zee says there are likely “several biological systems” that could explain why some people seem able to wake up without an alarm clock at a given time. It’s possible that worrying about getting up somehow “suppresses” our core internal clock, she says.
“This document is really interesting because it shows that your brain is still working,” she says.
Of course, how exactly it works and to what extent you can rely on this enigmatic internal alarm system remains a big unanswered question. And while none of the sleep researchers I spoke to are considering giving up their alarm clocks, Harvard’s Stickgold says he’s not ready to dismiss the issue.
“It’s a real scientific mystery,” he says, “that we have a lot of.” And as in many areas, he adds, when faced with a mystery, it would be arrogant “to assume that since we don’t know how it could happen, it can’t happen.”
This story is part of NPR’s periodic science series “Finding Time – A Journey Through the Fourth Dimension to Learn What Motivates Us.”
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