How Living in Total Darkness Sabotages Your Sleep

When study participants Josie Laures and Antoine Senni emerged from separate caves in the French Alps after more than 12 weeks in total isolation, researchers discovered they had lost weeks of their lives.

Laures surfaced on March 12, 1965, 88 days after she first entered her cave. She thought it was Feb. 25. Senni surfaced from his hole on April 5 that same year after 126 days away from sunlight. He thought it was Feb. 5.

The feat earned Laures and Senni each world records at the time for longest time spent alone in a cave. But the real winner was science. During each of the cave explorers' solitary adventure without sunlight to give them hints as to the time of day, researchers found that both Laures and Senni's perceptions of time as well as their sleep patterns were drastically altered while they were underground.

Senni, for one, would sometimes drift off to sleep for 30 hours at a time and wake feeling as if he'd simply had a short nap. Laures' sleep patterns were apparently so discombobulated that she struggled to fall back into a normal sleep pattern after coming out of her cave in the Alps.

Similar research in the decades that followed found that people's bodies tend to adjust into new sleep-wake patterns when they are isolated from sunlight, making them lose all concept of time.

So why does that happen? And what does it do to our mental state if we lose track of time?

We asked Jonathan S. Emens, M.D., F.A.B.S.M., a board-certified sleep medicine doctor and associate professor of psychiatry at Oregon Health & Science University, to shed some light on this mysterious phenomenon. To begin, he says, we must first understand what makes our internal clocks tick.

What Regulates Our Internal Clocks?

Our bodies are wonderous machines fitted with internally regulated cycles that rise and fall over a 24-hour period. These cycles are known as circadian rhythms and they play an important role in helping us fall asleep at night and wake in the morning.

The circadian rhythm is driven by an internal clock, sometimes called a circadian clock, that sets the timing for processes such as hormonal activity, body temperature, eating and digesting, and sleep/wake cycles.

"You can think of it like your heart — the pacemaker in your heart spontaneously generates the rhythm in electrical impulses that ultimately cause your heart to beat," says Emens, whose research focuses primary on circadian rhythm sleep disorders. "We similarly have a pacemaker in our brain — the suprachiasmatic nuclei (SCN) in the hypothalamus spontaneously generate a near-24-hour rhythm."

You can think of the cardiac pacemaker's full cycle being one beat per second — or 60 beats per minute — while the circadian pacemaker generates one full cycle every 24 hours or so.

Antoine Senni (center, rear) poses with some other cavers at the Aven de l'Olivier chasm, March 7, 1969. In 1965 he spent 126 days in a cave with no sunlight.
Keystone-France/Gamma-Rapho via Getty Images

There are a variety of environmental time cues (called zeitgebers) that can reset the circadian pacemaker such as the timing of physical activity, caffeine and shift work, to name a few. "However, the primary regulator of circadian timing is light, specifically through the eyes," he says.

The retinas in our eyes have special cells called intrinsically photosensitive retinal ganglion cells, or ipRGCs, that, along with the rods and cones, send light information directly to the SCN via a monosynaptic connection. This connection can even be made through the eyelids and can be triggered by some forms of artificial light.

"The circadian pacemaker will be reset to an earlier or later time and to a greater or lesser extent depending on the timing, intensity, duration and wavelength(s) of light to which we're exposed," Emens says.

How Does Being Stuck in Total Darkness Affect Sleep-Wake Cycle?

The best data on our biological clocks comes from a PNAS study which found that, on average, the length of the biological day is 24 hours and nine minutes.

It's actually a little shorter than that in women and a little longer in men, on average. "In other words," Emens says, "our clock isn't on an exactly 24-hour rhythm." Most of us stay on a roughly 24-hour rhythm because our clocks are regularly reset by sunlight.

The circadian clock works like, well, clockwork. Unless environmental factors cause that clock to go haywire — for example, isolating someone from all light, like putting them in a cave for months at a time.

In that situation, Emens explains, "the timing of the circadian pacemaker would start to shift to a progressively later, or earlier, time each day depending on whether they had a circadian rhythm that was greater than 24 hours or less than 24 hours."

If someone continues to live in complete darkness, the timing of the circadian pacemaker would continue to drift later, or earlier, in accordance with the individual's internal cycle length, he says. And if the person remains in the dark long enough, their cycle would drift around the clock.

And that can have some bad effects. Laures, who spent 88 days in total darkness, told the Associated Press after leaving her cave that "it became very difficult toward the end and I felt terribly worn out... At the start of my stay I read, and then I lost the desire... I listened to music... and knitted ... and looked forward to the time when I would finally see the sun."

Disruptions in circadian rhythms have been linked to mood disorders in certain individuals. In fact when the 33 Chilean miners were trapped underground for 69 days in 2010, special lighting was sent down to help them replicate their day and night cycles.

Chilean miner Juan Illanes celebrates after being brought to the surface on Oct. 13, 2010, following a 10-week ordeal in the collapsed San Jose mine in Chile.
MARTIN BERNETTI/AFP via Getty Images

However, after period of total darkness long enough for the sleep-wake cycle to be disrupted, a good dose of sunlight should be enough to reset the circadian pacemaker and get back on a more 24-hour cycle.

Does Blindness Affect Sleep-Wake Cycles?

If your eyes can't communicate light to your SCN, then your circadian rhythm can't respond to the trigger, which can result in your sleep-wake cycle being disrupted. Such is the case in about 55-70 percent of people with total blindness — those without absolutely no light perception, Emens says.

"As a result, the timing of the circadian pacemaker, along with all the many, many rhythms under its control, all drift to a progressively later or earlier time each day," he says. "This includes the circadian regulation of sleep and wakefulness."

This condition in totally blind people, which Dr. Emens has researched specifically, is known as non-24-hour sleep-wake rhythm disorder, or simply non-24. Most people with non-24 maintain a 24-hour schedule of activity, work, socializing and attempted sleep and wakefulness. However, because of the timing of the pacemaker drifting in and out of sync of the 24-hour day, they suffer bouts of nighttime insomnia and daytime sleepiness when the pacemaker is out of synch alternating with a relatively symptom-free period when the pacemaker is in synch.

In January 2014, the U.S. Food and Drug Administration (FDA) approved the first medication to treat non-24 in people who are totally blind. Hetlioz contains the active ingredient tasimelteon, which works similarly to melatonin. It helps to reset the master body clock in the SCN and remains the only FDA-approved drug for this condition.