Daylight Savings: How an Imposed Time Change Alters Your Brain, and What You Can Do

Michael Merzenich, PhD


March 08, 2022

On March 13, most of the United States and Canada will advance the clock an hour to be on Daylight Saving Time. Most other countries in the Northern Hemisphere will do the same within a few weeks; and many countries across the Southern Hemisphere turn the clock back an hour around the same time. A friend of mine, who spent time on Capitol Hill, once told me that whether it's adjusting to Daylight Saving Time (and losing an hour of sleep) or switching back to Standard Time (and picking up an hour), large numbers of Americans call their member of congress every season to complain.


Why are so many of us annoyed by the semi-annual resetting of clocks? It turns out that there are biological reasons for our discomfort with time changes. Those reasons also come into play when we change time zones as we travel, when we work on the night shift, or when we live at higher latitudes, where depressive symptoms from seasonal affective disorder (SAD) can plague us as the period of daylight progressively shortens in winter.

Our Internal Clock(s)

Each of us has a biological master clock keeping track of where we are in our 24-hour day, making ongoing time-of-day-appropriate physical and neurologic adjustments. We refer to those automatic adjustments as "circadian" rhythms — from the Latin, for "around a day" rhythms.

One of the most important regulated functions that is influenced by this time keeping is our sleep-wake cycle. Our brain's hypothalamus has a kind of "master clock" that receives inputs directly from our eyes, which is how our brain sets our daily cycle period at about 24 hours.

This master clock turns on a tiny structure in our brains, called the pineal gland, to release more of a sleep-inducing chemical, called melatonin, about the same time every evening. The level of melatonin slowly increases to reach maximum deep sleep in the night, then slowly declines as you advance toward morning awakening. The shift from darkness to daylight in the morning, causing your initial morning awakening, releases the excitatory neuromodulator norepinephrine, which, with other chemicals, "turns on the lights" in your brain.

That works well most of the time — but no one told your brain that you were going to arbitrarily go to bed an hour earlier (or in the fall, later) on Circadian Rhythm Time!

We also obviously shift the time on the mechanical clock — requiring a reset of the brain's master clock — when we travel across time zones or work the night shift. That type of desynchronization of our master clock from the mechanical clock puts our waking and sleeping behaviors out of sync with the production of brain chemicals that affect our alertness and mood. The result may be that you find yourself tired, but not sleepy, and often grumpy or even depressed. As an example, on average, people who work the night shift are just a little bit more anxious and depressed than people who get up to rise and shine with the sun every morning.

Seasonal Affective Disorder

An extreme example of this desynchronization of the master clock can manifest as SAD. SAD is a type of depression that's related to seasonal transitions. The most commonly cited cases of SAD are for the fall-to-winter transition. In North America, its prevalence is significantly influenced by the distance of one's place of residence from the equator — with about 12 times the impact in Alaska vs Florida. Of note, a weaker effect of latitude has been recorded in Europe, where more settled populations have had thousands of years to biologically and culturally adapt to their seasonal patterns.

What Can We Do About Our Clocks Being Messed With?

The most common treatment for SAD is light therapy, in which patients sit or work under artificial lights in an early-morning period, to try to advance the chemical signaling that controls sleeping and waking. Alas, light therapy doesn't work for everyone.

Another approach, with or without the lights, is to engage in activities early in the day that produce brain chemicals to contribute to bright and cheerful waking. Those "raring-to-go" brain chemicals include norepinephrine (produced when you encounter novelty and are just having fun), acetylcholine (produced when you are carefully paying attention and are in a learning and remembering mode), serotonin (produced when you are feeling positive and just a little bit euphoric), and dopamine (produced when you feel happy and all is right with the world).

In fact, you would benefit from creating the habit of starting every day with activity that wakes up your brain. I begin my day with computerized brain exercises that are attentionally demanding, filled with novelty, and richly neurologically rewarding. I then take a brisk morning walk in which I vary my path for the sake of novelty (pumping norepinephrine), pay close attention to my surroundings (pumping acetylcholine and serotonin), and delight in all of the wonderful things out there in my world (pumping dopamine). My dog Doug enjoys this process of waking up brain and body almost as much as I do! Of course, there are a thousand other stimulating things that could help you get your day off to a lively start.

If you anticipate feeling altered by a time change, you could also think about preparing for it in advance. If it's the semi-annual 1-hour change that throws you off-kilter, you might adjust your bedtime by 10 minutes a day for the week before. If you are traveling 12 time zones (and flipping night and day), you may need to make larger adjustments over the preceding couple of weeks. Generally, without that preparation, it takes about 1 day per time zone crossed to naturally adjust your circadian rhythms.

If you're a little lazier, like me, you might also adjust to jet lag by not forgetting to take along your little bottle of melatonin tablets, to give your pineal gland a little help. Still, that pineal gland will work hard to tell you to take a nap every day — just when you'll probably want to be wide awake.

And if, after reading this column, you find yourself still annoyed by the upcoming 1-hour time change, you might just look around at what's happening out there in the world and decide that your troubles are very small by comparison, and that you should delight in the "extra" hour of sunshine each evening!

Michael Merzenich, PhD, is often credited with discovering lifelong plasticity, with being the first to harness plasticity for human benefit (in his co-invention of the cochlear implant), and for pioneering the field of plasticity-based computerized brain exercise. He is professor emeritus at UCSF and a Kavli Laureate in Neuroscience, and he has been honored by each of the US National Academies of Sciences, Engineering, and Medicine. He may be most widely known for a series of specials on the brain on public television. His current focus is BrainHQ, a brain exercise app.

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