Illustration: Alexis Jamet

Elemental Light Week

Darkness Can Do All Kinds of Things to Your Body and Brain

In the absence of light, how do your body and mind behave?

This story is a part of Elemental Light Week, a five-day series on what light does for your body, brain, and well-being.

InIn 1962, French geologist Michel Siffre started going underground. He conducted a series of experiments that involved sending human subjects — including himself — into dark caves alone, for months, without any clocks or calendars or contact with the outside world, aside from daily check-ins with his research team above. The subjects lived in total darkness except for a lightbulb that would turn on when they awoke and off when they went to sleep.

Siffre’s goal was to study isolation, but in the process, he wound up showing that humans have a biological clock: an internal mechanism that controls when the body sleeps and wakes, among other functions. In the cave, without exposure to natural light, his subjects’ internal clocks fell out of sync with the 24-hour day/night cycle taking place above, warping their sense of time. Some fell into a 48-hour rhythm, sometimes staying awake for 36 hours and then sleeping for 12. When researchers told them their experiments were over, some subjects were surprised, believing they still had weeks or even months left to go.

Siffre’s work formed the foundations of chronobiology, which may explain why darkness seems to have such a profound impact on our bodies and minds.

The problems with darkness

In the cold, short days of winter, the darkness outside seems to correlate with a darkened mood within us; it’s an observation that goes back at least as far as Hippocrates. Modern science has shown that January and February are the hardest months of the year for the 6% of Americans who suffer from seasonal affective disorder (SAD), with symptoms including poor concentration, oversleeping, feelings of worthlessness, and weight gain.

But darkness can affect us all, and in surprising ways. Science suggests that darkness can do all kinds of things to the human body and brain: It can make us more likely to lie and cheat, make mistakes at work, and even see things we don’t normally see.

“Darkness is like a mirror: It shows you what you don’t want to see.”

“Everybody is responsive in one way or another to light and dark,” says Norman Rosenthal, a clinical professor of psychiatry at Georgetown University Medical School and author of the book Winter Blues.

To understand what darkness does to your body and mind, you first need to understand the effects of light: Your internal clock gets activated when light coming in through the eye stimulates a part of the hypothalamus called the suprachiasmatic nucleus. This, in turn, sends signals to other parts of the brain that start waking the body.

Without bright morning sunlight to reset it every day, your internal clock will increasingly run out of phase. “If our internal clocks get signals of alternating light and darkness, they can stay on 24 hours,” adds Josephine Arendt, professor emerita of endocrinology at the University of Surrey in England. “If they don’t have this information, the clocks usually run out of sync with the 24-hour day. For most people, that means they get up later and later.”

Because people living at extreme latitudes experience more winter darkness than those living closer to the equator, which gets a balanced 12 hours of light and dark all year round, researchers have theorized that the farther away you live from the equator, the more out of whack your internal clock might get.

Beginning in the 1980s, Arendt started studying workers at a base in Antarctica, where the sun does not rise at all for 110 days in winter, and found that their melatonin rhythms were delayed. Such circadian desynchrony has a range of negative effects: It can affect job performance, mess with your sleep, and even, in the case of night-shift workers, raise the risk of contracting certain cancers and metabolic syndrome.

More recently, a 2015 study comparing rates of depression among workers in daylight-deprived Sweden (in the Arctic Circle) and equatorial Brazil found that Arctic workers were more prone to develop depression and more likely to feel like they weren’t getting enough sleep. A study of nurses in Alaska found that they made almost twice as many medication errors in the darkness of midwinter than they did in fall.

Rosenthal, who started studying the effects of darkness on health about 40 years ago, says there’s a genetic element to how people deal with prolonged darkness. Surprisingly, Icelanders, who live in darkness 19 hours a day in winter, have a lower incidence of SAD than people in other countries.

Culture seems to play a role as well. The World Happiness Report ranks Finland — a country whose northern regions don’t see the sun at all in winter — the happiest in the world. And adaptations like hygge, the Danish concept of intimate coziness and warmth, help Scandinavians enjoy the coziness that the dark months bring.

Regardless of where on the planet you live, the darkness of your environment can affect your health and even your behavior. In architecture, the term “sick building syndrome” has been used to describe, well, buildings that make the people who live and work in them sick, in part because they are too dark. Research has also shown that students who sat in darker parts of the classroom did worse on tests than their classmates who sat near a window. And a 2013 study found that dark environments made people more likely to lie and behave unethically.

The power of darkness

Philosophers have long touted the importance of embracing darkness along with light, from the dualism of yin and yang to Carl Jung’s concept of the shadow self (“I must have a dark side also if I am to be whole”). And Western scientists agree that when it comes to dark and light, balance is everything.

A longtime student of Indian spiritual traditions, Anoula Sifonios went to her first darkness retreat in Thailand in 2017 and was so floored by what she experienced that she soon started leading retreats of her own. In an echo of Siffre’s early experiments in caves, attendees spend nine days sleeping, eating, and meditating in total darkness, without any natural or artificial light at all.

“Darkness is like a mirror: It shows you what you don’t want to see,” Sifonios says. After just a day or two in the dark, she began seeing flickering lights behind her eyes. Then came the visions. “You start seeing geometric patterns, tunnels, buildings that are carefully carved and decorated, symbols from traditions you don’t know,” she says. “You really see all sorts of images as the subconscious mind is emptying out.”

Sifonios’ experience echoes findings from Canadian psychologist Donald Hebb’s legendary and controversial sensory deprivation studies from the 1950s, in which participants reported vivid, dreamlike hallucinations after just a few hours in isolation, anything from dogs and eyeglasses to squirrels marching through the snow and old men in bathtubs.

In 2007, German artist Marietta Schwarz undertook a similar experiment: She wore a blindfold for 22 days and dictated aloud everything she “saw” while hooked up to an MRI, including a leopard-print pattern and the opening credits of Star Trek. The scan showed her cerebral cortex lighting up just as it would were she not blindfolded.

“People talk about paleo diets. Let’s pay attention to paleo lighting.”

As author Will Hunt explains in his book Underground, this may happen because the brain is used to getting a constant stream of visual stimuli, and when that stream is suddenly cut off by total darkness, it starts making up its own.

For Sifonios, the visions stopped around day six and gave way to a profound sense of peace.

After the retreat, she found she needed less sleep and had tons of energy, and she noticed other physiological and psychological effects that lasted months.

“So many people are afraid of the darkness, because it’s like going into the unknown,” Sifonios says. “But there’s a sense of security inside darkness that people don’t guess they will find. Darkness has much more to offer than we imagine.”

Randy Nelson, a professor of neuroscience at the West Virginia University School of Medicine, wants us to remember how our ancestors lived when we’re thinking about darkness and light.

“People talk about paleo diets. Let’s pay attention to paleo lighting,” he suggests. “What was caveman lighting like? It was light during the day and dark at night. That seems like a reasonable path. It kind of reflects the past 3 to 4 billion years of evolution on this planet. Let’s do what evolution suggests might be the way to go.”

This story is a part of Elemental Light Week, a five-day series on what light does for your body, brain, and well-being.

Itinerant journo, ex @fulbrightprgrm Spain & @sipiapa_oficial in Mex, interested in siesta, travel, food, journalism, bicycles & bourbon.

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