Time Blindness and Body Clocks: The Chronobiology of Neurodivergent Sleep

Fri Nov 6 · Science

On July 16, 1962, a 23-year-old French geologist named Michel Siffre climbed down into a cave in the Alps to live alone, with no clock, no calendar and no sunlight. When his team on the surface called down to tell him the experiment was over, he thought it was August 20. It was September 14. [1]

He had lost almost a month. Not to sleep, exactly. To the simple fact that without the sun, his sense of time quietly drifted away from everyone else's.

The clock inside you

Your body has a clock. Nearly every living thing does. It's called the circadian rhythm, from the Latin for "about a day," and it runs on its own, even in a dark cave. [2]

In 2017 the Nobel Prize in Physiology or Medicine went to Jeffrey Hall, Michael Rosbash and Michael Young for working out the molecular machinery of this clock: genes and proteins in fruit flies that build up and break down in a roughly 24-hour loop. [2] It's a clock made of chemistry, ticking in your cells right now.

The important word is roughly. Left alone, the clock doesn't run at exactly 24 hours. Every morning, light resets it. That's what Siffre lost underground: the daily reset. [1][2]

Night owls are real

Some people's clocks run later than others. They're not lazy. Their bodies release melatonin, the hormone that signals "night," later in the evening.

A 2010 study in Biological Psychiatry looked at adults with ADHD who had chronic trouble falling asleep. Compared with both other adults with ADHD and a control group, their sleep started and ended later, and so did their dim-light melatonin onset, the evening moment when melatonin starts to rise. [3] Later research has linked adult ADHD more broadly with being an evening type and with a delayed sleep phase. [4]

Research on autistic people points in a related direction. A 2011 review found that a number of studies reported lower melatonin levels or atypical melatonin rhythms in autistic people, and that melatonin supplements improved sleep in many of the studies reviewed. [5]

So when you say your brain switches on at 11 p.m., there may be a chemical reason behind it. You're not imagining the night shift.

Time blindness

"Time blindness" isn't a formal diagnosis. It's the phrase many people with ADHD use for a familiar experience: time doesn't feel like a steady stream. There's now, and there's not now. A deadline next week and a deadline next year can feel equally far away, right up until they're today.

Researchers studying ADHD have documented differences in time perception and in estimating how long things take, though the picture is complicated and results vary across studies. [6]

That's the experience in a sentence: like Siffre in the cave, except the cave is portable.

Why 3 a.m. is when the ideas show up

Many of us know the feeling of a mind that wakes up just as the house goes quiet. The demands stop. The noise drops. Nobody's going to need anything from you for hours.

Some of that is chemistry: a later clock means your best hours are later. Some of it is probably environment: the night is the one time the world stops interrupting. Either way, a lot of the best thinking happens in a window the daytime world doesn't use.

The cosmic part

Every clock on Earth is ultimately set by a spinning planet. The sun comes up because we turn toward it. Your melatonin rises because, a few hours earlier, the planet turned you away from the light.

There's a Rust Cohle angle too. Our neat 24-hour grid of meetings and alarms is a human overlay. Underneath it, there are billions of slightly different clocks, each running a little fast or slow, all being nudged back into line every morning by the same star.

Some of ours just take a little more nudging. And honestly, when you're the one awake at 3 a.m. while the stars turn overhead, it's hard to feel like you're the one who's out of sync with the universe.

Sources

1. Foer, J. "Caveman: An Interview with Michel Siffre." Cabinet 30 (2008). https://cabinetmagazine.org/issues/30/foer_siffre.php
2. The Nobel Prize. "Press release: The Nobel Prize in Physiology or Medicine 2017." https://www.nobelprize.org/prizes/medicine/2017/press-release/
3. Van Veen, M. M. et al. (2010). "Delayed circadian rhythm in adults with attention-deficit/hyperactivity disorder and chronic sleep-onset insomnia." Biological Psychiatry 67(11). https://pubmed.ncbi.nlm.nih.gov/20163790/
4. Bijlenga, D. et al. (2013). "Body temperature, activity and melatonin profiles in adults with attention-deficit/hyperactivity disorder and delayed sleep: a case–control study." Journal of Sleep Research 22(6). https://doi.org/10.1111/jsr.12075
5. Rossignol, D. A. & Frye, R. E. (2011). "Melatonin in autism spectrum disorders: a systematic review and meta-analysis." Developmental Medicine & Child Neurology 53(9). https://doi.org/10.1111/j.1469-8749.2011.03980.x
6. Noreika, V., Falter, C. M. & Rubia, K. (2013). "Timing deficits in attention-deficit/hyperactivity disorder (ADHD): evidence from neurocognitive and neuroimaging studies." Neuropsychologia 51(2). https://doi.org/10.1016/j.neuropsychologia.2012.09.036