Like most creatures on earth, humans come equipped with a circadian clock, a roughly 24-hour internal timer that keeps our sleep patterns in sync with our planet. At least until genetics, age and our personal habits get in the way. Even though the average adult needs eight hours of sleep per night, there are “shortsleepers,” who need far less, and morning people, who, research shows, often come from families of other morning people. Then there’s the rest of us, who rely on alarm clocks.For those who fantasize about greeting the dawn, there is hope. Sleep experts say that with a little discipline (well, actually, a lot of discipline), most people can reset their circadian clocks. But it’s not as simple as forcing yourself to go to bed earlier (you can’t make a wide-awake brain sleep). It requires inducing a sort of jet lag without leaving your time zone. And sticking it out until your body clock resets itself. And then not resetting it again.
To start, move up your wake-up time by 20 minutes a day. If you regularly rise at 8 a.m., but really want to get moving at 6 a.m., set the alarm for 7:40 on Monday. The next day, set it for 7:20 and so on. Then, after you wake up, don’t linger in bed. Hit yourself with light. In theory, you’ll gradually get sleepy about 20 minutes earlier each night, and you can facilitate the transition by avoiding extra light exposure from computers or televisions as you near bedtime. (The light from a computer screen or an iPad has roughly the same effect as the sun.) “Light has a very privileged relationship with our brain,” says Dr. Jeffrey M. Ellenbogen, chief of sleep medicine at Massachusetts General Hospital and assistant professor of neurology at Harvard Medical School. While most sensory information is “processed” by the thalamus before being sent on its way, Ellenbogen says, light goes directly to the circadian system.
But recalibrating your inner clock requires more commitment — in the form of unwatched reruns or lost time with a spouse — than many people care to give. For some, it’s almost impossible. Very early risers and longtime night owls have a hard time ever changing, says David F. Dinges, chief of sleep and chronobiology at the University of Pennsylvania’s Perelman School of Medicine. Night-shift workers also struggle, he says, because they don’t get the environmental and social cues that help adjust the circadian clock. The most important of these cues, called zeitgebers (German for “time givers”) is sunlight. But a zeitgeber could also be a scrambled-egg breakfast or children coming home from school in the afternoon.
Besides computer screens, the biggest saboteur for an aspiring morning person is the weekend. Staying up later on Friday or sleeping in on Saturday sends the brain an entirely new set of scheduling priorities. By Monday, a 6 a.m. alarm will feel like 4 a.m. “If the old phase was entrained for a long time,” Dinges says, “the biology has a kind of memory of this.” In other words, he says, “it takes self-discipline.”
2011-11-28 23:23 编辑：kuaileyingyu