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How Seasonal Change and Time Changes Mess With our Brains

by Dr Henry Mahncke(more info)

listed in light and colour, originally published in issue 280 - August 2022


As we learned in school at a young age, the longest and shortest days of daylight come each June and December – with the extremes of darkness and daylight of these Winter and Summer Solstice days determined by how far above or below the equator you reside.  With the next Solstice arriving on June 21, let’s pause to look at how changes in your exposure to daylight affect the human brain, your mood, and performance, as well as what you can do about it.




Overview of biological circadian clock in humans
Biological clock affects the daily rhythm of many physiological processes. This diagram depicts the circadian patterns typical of someone who rises early in morning, eats lunch around noon, and sleeps at night (10 p.m.). Although circadian rhythms tend to be synchronized with cycles of light and dark, other factors – such as ambient temperature, meal times, stress and exercise – can influence the timing as well.


Our Internal Clock(s)

Each of us has a biological master clock keeping track of where we are in our 24-hour day. That internal clock is constantly making time-of-day-appropriate adjustments to your brain and body. We refer to these 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 brains set our daily cycle period at about 24 hours.



When eyes receive light from the sun, the pineal gland's production of melatonin
is inhibited and the hormones produced keep the human awake. When the eyes do not
receive light, melatonin is produced in the pineal gland and the human becomes tired.


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.

Some Illustrations of When your Circadian Rhythms get Messed With

A good illustration of how shifts in daylight wreak havoc with your internal master clock comes from rapidly crossing multiple time zones, as you do when you jet long distances. Your internal clock is set to the time zone you started in. When you travel 10 time zones – say from San Francisco to Sydney – your internal clock becomes more than a little miffed. Night and day seem to almost have switched and that 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. Yet, those who travel those kinds of distance at a much slower pace – perhaps by ocean liner – have far less issues, as they slowly make daily adjustments in their circadian rhythms.

We shift the time on the mechanical clock – requiring a reset of the brain's master clock – not just when we travel across time zones. Our minds and bodies are so sensitive to these rhythms that even the relatively small one-hour adjustments to our mechanical clocks as we go on and off Daylight Savings Time each spring and fall cause some people great annoyance.

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.

A similar example arises if you change suddenly from working the day shift to the night shift. At first, you will have a lot of issues, until your body adjusts to your new rhythms. However, even if you have been a night shift worker for a long time, night shift workers are apt to be just a little bit more anxious and depressed than people who wake 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 Seasonal Affective Disorder (or 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 which stretches from the Vernal Equinox in the Spring to the Winter Solstice.

SAD seems to be more prevalent in the Northern Hemisphere than in the Southern, which may be attributed to the amount of the population that lives a good distance from equator (as well as the tilt of the earth), which affects the average amount of daily exposure to sunlight. This is well documented in studies in North America, in which the prevalence of SAD is significantly influenced by distance from the equator – with about 12 times the impact in Alaska than Florida. Also of note, a weaker effect of latitude has been recorded in Europe, where more settled populations have had thousands of years to adapt (biologically and culturally) 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 the early morning, to try to advance the chemical signaling which controls your 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 start my day with computerized brain exercises which are attentionally demanding, filled with novelty, and richly rewarding. I take a brisk morning walk or ride my bike to work, and I vary my route for the sake of novelty (pumping norepinephrine), pay close attention to my surroundings (pumping acetylcholine and serotonin), and delight in the wonderful things I see (pumping dopamine). Of course, there are a thousand other stimulating things that could help you achieve a lively start to your day.

If you anticipate feeling knocked off your rhythms by a time change, you could also think about preparing for it in advance. If it's the adjusting clocks by an hour for Daylight Savings 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, it’s never a bad idea to listen to your body, seek out brightness to enliven your brain, and take a nap when you need to.


  1. Tom said..

    The time changes are extremely debilitating. I think they have kept them around for so many decades as another means to disrupt our bodies hoping that we will seek some form of nonsensical medical attention. Otherwise, the time changes serve no purpose although I think in a few years they are finally going to stop this destructive practice.

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About Dr Henry Mahncke

Dr Henry Mahncke got his PhD in Neuroscience at the University of California, San Francisco [UCSF] in the Merzenich Lab, which discovered the brain remains “plastic” – capable of chemical, structural and functional change – at any age. Then, at the request of his academic mentor, Dr Mahncke led a global team in harnessing that plasticity through the computerized brain exercises found in the BrainHQ app, which is produced by Posit Science, where he is the CEO. BrainHQ can be found at

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