Daylight Saving Time occurs every year during the month of March, but somehow people are always caught off guard—as undoubtedly will happen when we spring forward on Sunday, March 12, at 2 a.m. Professor of Psychology and Samuel R. Milbank Chair Peter D. Balsam—whose recent faculty research talk “The Brain is a Time Machine” explained how everything we think and do relies on coordinated and timed signals between the body and brain—pulls from decades of research in neuroscience to help simplify the complex job our brains have when negotiating daylight and time.

During your lecture in January, you talked about the brain’s role in anticipation. Why, then, are so many of us unprepared for Daylight Saving Time when we "lose" an hour every spring?

When we anticipate meeting a friend in a few hours or anticipate a holiday in a few weeks, we are using timing systems that tell us when important things will happen. These systems are very flexible and let us adapt to the wide range of situations we encounter in different environments. We learn to expect a red light to turn green in a minute or two, and we learn to expect to see an emergency vehicle shortly after we hear a siren. Those are all temporal expectations that we acquire through our everyday experience. We can learn to anticipate best when the signals are reliable predictors of what will happen.   

We can anticipate our birthday because it occurs on the same date every year, and by looking at a calendar we get a very reliable cue about when to expect the celebrating to begin. With events like DST that occur on different days every year, we don't get those same kind of reliable signals. So we have to wait for DST for our bodies to adjust to the change in our sleep patterns and in our exposure to light. Our circadian rhythms adjust to the light in different ways depending on when the extra light occurs. In general, if our day lasts longer when we fly east to west, that is an easier adjustment than in the opposite direction.

What is the circadian rhythm, and how is it affected during DST?

The circadian rhythm is a specialized timer that governs our sleep-wake cycles; the timer has approximately a 24-hour rhythm. It is a very accurate clock, and it is not tied to external stimuli—though some external stimuli like light exposure can shift the rhythm. Knowing that light is coming earlier or later than usual, as we do when we shift our alarm clock for Daylight Saving, does not change the circadian rhythm. Only [actual] exposure to light will change that rhythm.

How can we better mentally prepare for a national time change—short of going to bed an hour earlier?

Our sleep-wake cycles are mediated by a hormone called melatonin. Some people suggest taking a melatonin supplement about an hour before the new bedtime for a few days before the switch. Others suggest shifting your bedtime 10-15 minutes a day during the week before the shift. I have not seen data evaluating either approach, so I give no recommendations.  

During the lecture you said the slowing down of time appears to happen during emergencies or even when playing sports. Many people complain of that first day or week of DST as going slowly. Why do we feel that way?

For most people, it is harder to adjust to Daylight Saving Time than it is to adjust back to Standard Time in the fall. This is because we are getting an extra hour of light at the beginning of the period when our body and brain expect it to be night. The switch to Standard Time causes a slow shift in our circadian rhythms. It is a slow adjustment.

But I think another major influence on how we feel on the first days of DST is the result of being tired. Many of us are not tired when the clock tells us it is our usual bedtime. For example, if you usually sleep from 11 p.m. to 7 a.m., your alarm clock might say 11 p.m. on the first day of DST, but your body feels like it is 10PM. So you might not fall asleep until the clock says midnight. Your alarm at 7 a.m. still wakes you, but now you have only slept for seven hours rather than your usual eight. Even a slight sleep deprivation makes some people feel off. In the fall when everyone can have an extra hour of sleep, there is less complaining.

Click here for more on Prof. Balsam’s lecture about timing.



Barnard experts explain.