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Internal Time

Internal Time: Chronotypes, Social Jet Lag, and Why You're So Tired

Till Roenneberg
Copyright Date: 2012
Published by: Harvard University Press
Pages: 270
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  • Book Info
    Internal Time
    Book Description:

    Early birds and night owls are born, not made. Sleep patterns are the most obvious manifestation of the highly individualized biological clocks we inherit, but these clocks also regulate bodily functions from digestion to hormone levels to cognition. By understanding and respecting our internal time, we can live better.

    eISBN: 978-0-674-06548-2
    Subjects: Biological Sciences

Table of Contents

  1. Front Matter
    (pp. i-vi)
  2. Table of Contents
    (pp. vii-x)
  3. Introduction
    (pp. 1-7)

    This book is about clocks. Not about those you can buy, wear, or hang on a wall, but about the clock that ticks away in your body. The body clock is not a new invention in the long line of evolution. You share your ability to internally keep track of the time of day with practically every other creature on earth, from other mammals right down to those organisms that exist only as a single cell. This means that an internal biological clock must be extremely important for life on this planet. Living without or against the biological clock would...

  4. 1 Worlds Apart
    (pp. 8-15)

    Ann woke to a hard and persistent knock on her bedroom door. After staying in bed as long as possible, she wrapped herself into a thick bathrobe, put on warm socks, and stumbled to the bathroom to brush her teeth. She didn’t say “good morning” to her father and didn’t expect any form of greeting from him, either. If she hadn’t pushed him grumpily away from the basin to reach the faucet, one would have thought that neither was aware of the other. It was a school morning, shortly before the Christmas break. Ann was, as usual, far behind schedule...

  5. 2 Of Early Birds and Long Sleepers
    (pp. 16-23)

    The sun had just risen above the horizon when the farmer walked along a country path toward his field. He cheerfully greeted a man he encountered halfway between the village and his destination. He thought to himself, “Must be a decent bloke to be up so early.”

    The postman rang the doorbell at half past ten. If he hadn’t heard noises from within the apartment, he would have left long before. He rang the bell once more—longer and harder—and then heard a rather grumpy voice announcing the imminent appearance of its owner. “Lazy bugger,” thought the postman when...

  6. 3 Counting Sheep
    (pp. 24-30)

    Sergeant Simon Stein lay down on one of the mattresses lined up in long rows on the floor of a big windowless gym and wondered why he had signed up for this project. He and thirtyfour other soldiers had to perform a lot of psychological and physical tests at different times of the day over a certain period—exactly how long the project would last was still an open question. They were allowed to sleep one-third of the time but were tested during the rest. When first proposed, this sounded almost better than their usual routine, because Stein’s unit often...

  7. 4 A Curious Astronomer
    (pp. 31-35)

    On a lovely evening toward the end of the summer of 1729, the French astronomer Jean Jacques d’Ortous de Mairan sat at his desk working on a manuscript. He paused to think about a difficult sentence. As some of us do when we concentrate and turn our thoughts inward, he gazed out of the window into the cloudless evening sky. Although it was still bright enough to work without a lamp, the quality of the celestial light clearly announced the approaching night. He didn’t manage to capture his thoughts in words that his readers would unmistakably understand. His inward gaze...

  8. 5 The Lost Days
    (pp. 36-46)

    The young man sat at his desk looking extremely pleased with himself. He was on schedule; in two weeks his thesis would be finished. He got up and walked through his windowless studio apartment to the small kitchenette to put on some water for a cup of coffee. While waiting for it to boil, he added a couple of items to a shopping list lying on the kitchen counter—coffee, milk, butter, . . . After checking his list once more, he opened the solid, soundproof door of his apartment and placed the piece of paper on one of the...

  9. 6 The Periodic Shift Worker
    (pp. 47-59)

    It was seven o’clock when the alarm abruptly woke Harriet from deep sleep—she must have drifted off only a couple of hours ago. She angrily pressed the snooze button on her alarm clock and turned around again. She fell asleep immediately but was awakened a couple of minutes later by the alarm’s insistent reminder. This procedure continued for about another half an hour. Although she sensed that it was once again a magnificent summer morning, promising to be a wonderfully warm day, she felt like an ice cube and dog tired. In her half-conscious state she wondered how appropriate...

  10. 7 The Fast Hamster
    (pp. 60-65)

    A new shipment of hamsters from the Charles River Breeding Laboratories had arrived. Christopher was in the process of cataloguing the new animals. When he had entered them all into his files, he placed each one of them into a separate cage equipped with a running wheel. His first task with newcomers was to record their circadian activity rhythms—a routine to check whether they were good or bad runners. A couple of weeks later, he sorted through the pile of activity recordings and made his usual list: “good runner” or “bad runner.” A typical activity recording for hamsters living...

  11. 8 Dawn at the Gym
    (pp. 66-74)

    It was 5 A.M. when the family entered their 24/7 workout facility in Utah. A gray day with a slight drizzle had just begun. The large, cheerful group was quite a sight. There was great grandmother Sarah; her daughter and son, Alicia and Frederic; Alicia’s son and daughter, Phillip and Rebecca; Rebecca’s two teenage girls, Julia and Anna; and Frederic’s two youngsters, Peter and Jessica. It was almost the entire tribe. Only Sarah’s two sisters, Isabelle and Judith, were missing. They had arisen with the workout group but had stayed at home, responsible for the traditional family breakfast later on,...

  12. 9 The Elusive Transcript
    (pp. 75-80)

    To his great frustration, Oliver’s experiments had utterly failed for several weeks now. He was working on a project that concerned the biochemical and molecular regulation of liver metabolism, continuing the experiments of a Canadian postdoctoral fellow who had recently left the lab for his first job as a professor and scientist.¹ The experiments focused on a gene that was switched on in liver cells under certain conditions. Although Oliver had always meticulously followed the experimental protocols, he was never able to find the products that should have been present if the gene had been activated. Oliver had always been...

  13. 10 Temporal Ecology
    (pp. 81-89)

    The tiny creature danced, together with millions of others, below the surface of the ocean. They swam toward the sun, many of them to the same location, forming dense clouds. When the clouds reached a certain density, they suddenly seemed to become heavier than water and sank away from the water’s surface, glittering in the morning sun. The clouds dispersed into single creatures again, then immediately reformed and swam back up toward the sun. This repeating ritual created a tiny current, similar in shape to a magnetic field, drawing in other creatures at the surface. This accumulation made the clouds...

  14. 11 Wait until Dark
    (pp. 90-95)

    Someone always tended the fire in the center of the great cave. The clan had some kind of arrangement as to whose turn it was to watch the fire, but these arrangements were only for emergencies—just in the rare case that nobody was awake. Normally, someone would be awake at all times during the night and would come to sit around the fire to chat or just add some wood. No one was able to sleep through the entire stretch of a night’s darkness, except for the few short midsummer nights. Most members of the clan retired shortly after...

  15. 12 The End of Adolescence
    (pp. 96-105)

    Urf had been lying on the forest floor for a very long time but nothing had come along the trail so far. He had lost any sense for how long he had been lying there in almost complete darkness, surrounded only by the noises of the nocturnal forest. He and the other three hunters had left their dwellings at dusk and had walked for half of a summer’s night before reaching the part of the woods where they hoped to find the deer. It was a good place—the deer had to pass through a narrow opening between two mountains...

  16. 13 What a Waste of Time!
    (pp. 106-113)

    Jacob needed a smoke and persuaded Felix to leave campus with him during the first morning break. He was in a really foul mood. He had slept far too little, his parents were on his back about his current performance in school, and now that thing in class again. His mother had talked to the teachers of his worst subjects. As a reaction—probably well meant by the teachers—they suddenly generated frequent opportunities for him to get higher oral grades to compensate for the bad ones he was getting in most of the written exams.

    It had been the...

  17. 14 Days on Other Planets
    (pp. 114-128)

    It is the year 2210. The world never really recovered from the big economic depression two hundred years ago. Concern for the environment and nature goes down the drain in times of financial hardship. As a consequence, many regions of our globe have become unlivable for most plants, animals, and humans. The area usable for human settlements has been reduced to a tenth of what was available around the turn of the millennium and continues to decrease rapidly. Places to live are not the main problem—humans have retreated to higher regions, shielded from the rising ocean levels, or live...

  18. 15 When Will My Organs Arrive?
    (pp. 129-138)

    It was 7 P.M. when Oscar, a middle-aged and slightly rotund surgeon, handed his new acquaintance two glasses: one with gin, tonic, lime, and ice; the other with plain tonic water. “I didn’t know how strong you want your G&T, so I brought some extra tonic,” he said. “I’m Oscar, by the way.”

    “Thanks for the drink, Oscar. My name is Jerry.”

    When Oscar had settled in one of the comfortable, overstuffed leather armchairs, he raised his glass, which appeared to contain a Bloody Mary. “Cheers.” After taking a sip, he put the glass down on the stylish glass table...

  19. 16 The Scissors of Sleep
    (pp. 139-151)

    After graduating from high school, Timothy had visited Benjamin at Princeton University and had worked in his friend’s small start-up company. Ever since they lived on the same street in a suburb of Eugene, Oregon, they had been the closest friends, even though Benjamin had been the classmate of Timothy’s elder brother. The six months in Princeton had been Timothy’s first taste of independence away from home and had been heaven on earth. He loved Princeton, with its university and its sidewalk cafés.

    Benjamin had opened a small shop called LayIn&Out—a sophisticated kind of copy shop and café. Besides...

  20. 17 Early Socialists, Late Capitalists
    (pp. 152-162)

    Olaf Toemmelt is the director of GoEast, an extremely successful public relations agency based in Magdeburg, East Germany. The State of Saxony-Anhalt has launched a competition for a public relations campaign that would help to attract more businesses and boost the state’s economy. Together with his team, Olaf had been brainstorming for almost a week now, but none of the ideas had been convincing enough to develop into anything that could be used for the competition. It was a beautiful summer morning, and he drove to work in his open BMW convertible from his country house—an old vicarage he...

  21. 18 Constant Twilight
    (pp. 163-172)

    Sophie sat at her favorite spot in the alcove window overlooking the valley. After everyone else had gone to bed, she had switched off the lights to see the beautiful starry night outside. A full moon was just about to climb over the ridge of mountains, and its solar reflections bathed the valley in the most magical light. Her thoughts went back to those terribly confusing months when none of them had any idea about how to solve the gridlocked situation. Before everything had started to turn upside down and inside out, they had been a happy and normal extended...

  22. 19 From Frankfurt to Morocco and Back
    (pp. 173-183)

    Edgar Mass made little notes in his small note book. He had been up before the sun to measure all aspects of dawn right up to actual sunrise.¹ He stopped making measurements when exactly half of the sun’s disc had risen above the horizon. He added some last entries to the long lists and tables he kept in his little black notebook. His handwriting was tiny but immaculately clear. He packed away the small devices he always carried with him to track the sun during the day and the stars at night: a tiny monocular telescope of excellent quality; a...

  23. 20 Light at Night
    (pp. 184-192)

    Marco Gonzales took the call and looked at his computer screen that showed him all the details of the weather in Manchester. “Good morning, Mrs. Taylor. How are you today? Isn’t it great that it finally stopped raining?” Marco had just started work and Mrs. Taylor’s call to the bank was the first of an endless series he would be taking for the next twelve hours. “My name is Marco. How can I help you?” Mrs. Taylor asked him to pay a doctor’s bill from her account. She was elderly and handicapped and wouldn’t have known how to bank online...

  24. 21 Partnership Timing
    (pp. 193-201)

    Louise was dead tired but just couldn’t find sleep. Normally she didn’t mind that Bruno was still reading beside her. But tonight he seemed to flip his pages especially loudly, and his bedside lamp appeared brighter than usual. After a lot of tossing and turning, of rearranging her duvet, of sighing deeply and frequently, she opened her eyes and turned to her husband. “Bruno,” she said in a suffering voice, “would you mind not reading tonight? I just can’t fall asleep.”

    Now Bruno sighed deeply. “All right, I’ll sleep in the guest room,” he replied. He took his book and...

  25. 22 A Clock for All Seasons
    (pp. 202-213)

    It was 7 P.M. on the twenty-second of September when Gerry’s cell phone started to play Pink Floyd’s “Time” from the album Dark Side of the Moon. Barbara’s phone went off simultaneously, playing Nat King Cole’s “You Are My Sunshine”—she loved sentimental 1940s music. The two phones produced a rather cacophonous concert but Barbara and Gerry seemed not to mind. They were driving home to their suburban row house after having visited a friend who worked as a scientist at the local hospital’s psychiatric unit. The sun had almost completely set when the phones went off, and Gerry handed...

  26. 23 Professional Selection
    (pp. 214-222)

    The conference dinner had long been over. About thirty neurosurgeons had gone to a jazz bar in the old part of town to celebrate a successful meeting. The core of the party consisted of three neurosurgeons—among the best in the world—who had known each other for decades. Their frequent joint appearances had earned them the nickname “the three-pack.” Many of those who attended these conferences regularly had learned over the years to follow wherever the three-pack led—especially when Drs. Fergusson, Skinter, and Lafayette went to a jazz bar.

    A quartet (bass, saxophone, piano, and drums) was playing...

  27. 24 The Nocturnal Bottleneck
    (pp. 223-232)

    The three older boys always thought that their slightly chubby, red-haired, freckled-face little brother Leon was a bit peculiar because he seemed more interested in strange self experiments than in kicking a ball with them in the garden. Leon’s most recent project was to find out how the brain works. It had started last Monday when Professor Mallet, the father of a classmate who was a scientist at the local university, had talked to their biology class about how the brain functions. From that day on, Leon had been looking at the world through different eyes. He began to think...

  28. Notes
    (pp. 235-262)
  29. Acknowledgments
    (pp. 263-264)
  30. Index
    (pp. 265-272)