6.Although men could go on fathering babies until a much older age or even until they die, the statistical chances that they actually do so are very rare.
7.Isocaloric meals are meals that contain exactly the same amount of calories.
13. What a Waste of Time!
1.See, for example, M. A. Carskadon, C. Acebo, and O. G. Jenni (2004). Regulation of adolescent sleep: implications for behavior. Annals of the New York Academy of Sciences 1021:276–291. Dr. Carskadon teaches at Brown University School of Medicine in Providence, Rhode Island.
2.Narcolepsy is caused by a defect in a neurochemical pathway of the brain. Researchers are beginning to find genes associated with this inheritable disease.
3.REM stands for a sleep stage that produces rapid eye movements. The brain’s activity can be recorded via multiple electrodes attached to the head. This method is called electroencephalography (EEG). The states of wakefulness and different sleep stages can be distinguished by the waveforms of the EEG.
4.F. Danner and B. Phillips (2008). Adolescent sleep, school start times, and teen motor vehicle crashes. Journal of Clinical Sleep Medicine 4:533–535. Conducted at the University of Kentucky in Lexington.
5.C. Randler and D. Frech (2006). Correlation between morningness–eveningness and final school leaving exams. Biological Rhythm Research 37:233–239. Conducted by Christoph Randler of the University of Heidelberg.
6.This school is the Centret Efterslaegten in Copenhagen.
14. Days on Other Planets
1.C. Gronfier, K. P. Wright, R. E. Kronauer, and C. A. Czeisler (2007). Entrainment of the human circadian pacemaker to longer-than-24-h days. Proceedings of the National Academy of Sciences USA 104:9081–9086. Gronfier undertook this work with Charles Czeisler at Harvard.
2.Zeitgebers are all environmental signals that can synchronize the circadian clock. The most potent zeitgeber is the light–dark cycle.
3.Please excuse the pun, especially since Armstrong made his famous small step on Earth’s natural satellite and not another planet.
4.The range that is between these limits of entrainment is called range of entrainment.
5.The prediction that the internal days of the family at the gym in Utah are very short has been experimentally proven for those family members who carry the mutation. This was true both for their behavioral rhythms as well as for rhythms recorded in tissues grown from cells of these individuals. See K. L. Toh, C. R. Jones, Y. He, E. J. Eide, W. A. Hinz, D. M. Virshup, L. J. Ptáek, and Y-H. Fu (2001). An hPer2 phosphorylation site mutation in familial advanced sleep phase syndrome. Science 291:1040–1043.
15. When Will My Organs Arrive?
1.People suffering from asthma normally have their worst attacks around 4 A.M. That is why Oscar saw the bright side of jet lag, because for the first time in many nights he was able to sleep without being awakened by an attack.
2.Oscar had to repeat his sentence because Jerry had dozed off. Remember Jerry’s clumsiness and his inability to punch in the correct numbers for his home phone.
3.Interestingly, the most active field that investigates the consequences of jet lag and tries to find powerful solutions to the problem is sports medicine. Successful athletes have to perform at different locations around the globe with very little time to adjust between games. Since a difference of milliseconds can come between the performance of an athlete and a medal, combating jet lag is crucial.
4.Early chronotypes reach this performance dip before late types lose their cognitive skills.
5.Recall Jerry, who alternated between a hysterical laughing fit and utter depression.
6.The principal investigator of these studies was Michael Menaker, whose lab is featured in my story about the hamster with a fast clock in an earlier chapter. To record circadian rhythms, animals are normally kept in cages including a running wheel, with a computer recording the wheel’s rotations. Several cages are usually grouped together in a bigger box, which has temperature and air control but is isolated from other boxes in the room. Each of these boxes has its own computer-controlled light source, so an investigator can easily introduce sudden shifts of the light–dark cycle, simulating, for example, a flight from Boston to Tokyo. The experimenters can then investigate the consequences for behavior, organs, or tissues. In the jet lag experiments described here, the scientists advanced or delayed light–dark cycles by six to nine hours. They then investigated the specific adjustment of different tissues by recording the respective circadian rhythms with the help of so-called reporter constructs. These constructs have revolutionized circadian research by taking advantage of the fact that some organisms produce light with the help of a biochemical reaction called bioluminescence. You know the phenomenon of bioluminescence from the glow of the marine algae you read about, or you may have seen it in fireflies, or have heard of it with regard to the glowing wounds of First World War soldiers. In World War I this phenomenon was caused by bioluminescent bacteria that had infected the wounds. Bioluminescence is controlled by a specific enzyme, called luciferase. Steve Kay and Andrew Millar were the first scientists to genetically engineer plants and later fruit flies so that the luciferase gene was put under the control of DNA elements that normally control clock genes. The amazing outcome of this genetic engineering was organisms or even individual organs or tissues that produced a glow that waxed and waned approximately once a day.
7.Normally laboratory animals can feed whenever they want (ad libitum) by simply going to the food container that is part of their cage. Restricted feeding means that access to the food container is controlled by a shutter. In this way the experimenter can dictate at what times of day the animal can feed.
16. The Scissors of Sleep
1.I have known people who claim to use several alarm clocks in a row, some even placed in empty metal buckets to increase the sound effect. In this case, the entire assembly of clocks and buckets could be summarized under the acronym WUA.
17. Early Socialists, Late Capitalists
1.“Ossie” is a derogative expression for those people who were citizens of the former socialist German Democratic Republic, GDR. The moniker derives from the German word for east (Ost). Those from West Germany are called “Wessies.”
2.The protagonists of this chapter’s story, their public relations firm, and other details are completely fictional, but it’s a fact that Sachsen-Anhalt was looking for a new image and found it in the slogan “We get up earlier.”
3.What the commentator probably means by “the dog’s morning newspaper” are the new odors he “reads” with his nose on his morning walk, which he wants to do as soon as he wakes up at the crack of dawn.
4.Chennai was once known as Madras.
5.To be certain about the authenticity of an individual’s geographical location, I was extremely rigorous in my selections. Only those entries in which the postal code and the name of the village, town, or city corresponded without any doubt were chosen for the analysis. Any questionable entry was discarded, even if it was clear that the mistake had apparently been only an accidental exchange of two digits.
6.Think of the disco argument used to explain lateness in adolescents or the belief that every human can—with a bit of discipline—get used to almost any work schedule, or think of my colleague’s reaction to the results from India.
7.You may have asked yourself why, in the days of a unified Germany, I have included the former GDR frontier in the small grey inset of the first figure in this chapter—now you know.
8.On the contrary: Germany’s two southern states, Bavaria and Baden-Wuerttemberg, are traditionally more conservative than the rest of the country, especially toward the east. They are also very homogeneous in their culture.
9.China is measured here in degrees, which are different from miles or kilometers. You can theoretically walk “around the world” in a couple of minutes when you are standing very close to one of the poles, but you would have to cover 40,000 kilometers close to the equator.
10.Mid-dark and midnight coincide precisely only twice a year; due to astrophysical characteristics, mid-dark undulates around midnight, deviating approximately by fifteen minutes in either direction; these deviations are independent of location.
11.This essentially means that they eat at the same sun time. When it is 10 P.M. in Spain it is only 9 P.M. in Portugal.
12.I am not trying to explain the world on the basis of the body clock—in most cases there are many reasons behind almost everything. But I do think that an exclusively sociocentric view of human activity has to be somewhat counterbalanced. Of course, eating habits do not show only an east–west but also a north–south gradient. Then again, the supposedly “cultural” differences may in fact be environmental, such as temperature.
18. Constant Twilight
1.The fact that Joseph and Frederic are identical twins means that they have the same genes. The fact that they grew up under identical circumstances means that any modifications made to their genes during their childhood are also likely to be the same. Genes, or rather their capacity to make proteins, can be altered during one’s lifetime, depending on the conditions we live in. This phenomenon is called epigenetics.
2.Lux is a unit for light intensity specially adapted to human vision.
3.Amplitude is a measure of the difference between the high and low points of a cycle, in this case the light–dark cycle.
4.The effect of light on changing clock speed saturates at some intensity, so that more light has no additional effect.
5.“Frische Luft macht müde.”
6.Lack of light may cause depression. Hanna’s depression was surely triggered by catching her husband in Sophie’s arms, but lack of light made it even worse; exposure to more daylight eventually helped her to get out of it.
19. From Frankfurt to Morocco and Back
1.Dawn starts when the first twilight can be seen well before the sunrise, whereas sunrise marks the moment when the edge of the sun appears above the horizon. The duration between dawn and sunrise depends on latitude. At the equator dawn and sunrise are so close that it seems as if the lights were switched on to start the day; in polar regions the time from dawn to sunrise can take hours. One distinguishes several levels of dawn: astronomical—the sky is no longer completely dark (the sun is still eighteen degrees below the horizon); nautical—there is enough sunlight to actually see the contour of the horizon (the sun is still twelve degrees below the horizon); civil—there is enough light available to permit outdoor activities (the sun is still six degrees below the horizon).
2.Of course it is not the sun that “takes” that time, but the earth’s rotation that exposes different parts of the globe to the sun.
3.The package contained the Munich ChronoType Questionnaire (MCTQ). The sleep logs are a kind of daily MCTQ containing questions like these: When did you go to bed? When did you switch off the lights? How long did it take to fall asleep (sleep latency)? When did you wake? When did you get out of bed (sleep inertia)? How alert did you feel at bedtime and at wake-up? Did you use an alarm clock? How well did you sleep? How much time did you spend outside without a roof over your head? Was today the morning of a work day or a free day?
4.Black bars (SET) indicate the times when people live by standard European time. White bars (DST) indicate when people live on summer time.
5.The equinox is the date when day and night are exactly twelve hours long; in the northern hemisphere the spring equinox is on March 22.
6.Of course, actimeters only record activity, so that we can merely guess when the subjects slept. To be sure about their actual sleep times, we would have to make polysomnographic recordings, such as EEG, records of eye movements, and so on.
7.The times in this graph are given only as a reference. We normalized the average of the activity onsets during the first four weeks of the experiment for each subject to 7 A.M. (SET) and then calculated the weekly changes in reference to this time. Thus, if a volunteer perfectly adjusted to a DST change, he or she would get up one hour earlier or later after the change, although local time would not change.
8.This translates to September in the southern hemisphere. The actual times of year when the clocks are changed to and from DST differ from country to country. The United States, for example, has recently decided to extend the period of DST, moving the spring switch even earlier and the autumn switch even later.
9.I have used the expression “time change” in this chapter only because it is commonly used in reference to DST. In reality, it is yet another way to make us believe that DST is a normal procedure. DST transitions do not change time, of course! All we do is change our modern clocks. I specify “modern” here because more ancient devices, like the sundial, could only be changed by bending the rod that throws the shadow twice a year.
20. Light at Night
1.Indoles are a class of molecules that form ring structures of carbon atoms. If these structures contain nitrogen (amines), they are called indolamines.
2.Today, oxygen makes up 21 percent of our planet’s atmosphere, which initially was oxygen-free. When photosynthesizing organisms started to produce this potentially extremely aggressive molecule, they killed off most of the species that hadn’t adapted their metabolism to the new situation. Like many other molecules, oxygen comes as a pair, O2, where it is harmless. But when chemical reactions take one of the pair away and leave the other with an electric charge, this “radical” is so reactive that it can initiate uncontrollable reactions with other molecules, such as DNA. Organisms existing after the plant revolution had to evolve countermeasures to scavenge free oxygen radicals. There are many different kinds of radical scavengers in the biochemistry of our cells, including the indolamines.
3.The LAN hypothesis is also a good example of the fact that a combination of correct statements doesn’t necessarily make a correct hypothesis. To date, there is no good evidence for or against the hypothesis that melatonin suppression directly causes cancer. It also should be noted that melatonin levels are extremely variable from individual to individual. In some healthy people it cannot even be detected at any time of day or night.
4.Please note that I specifically have chosen a nonexisting pathology. There is no earlobe cancer; there is only skin cancer, which can develop anywhere, including the earlobe.
5.In a general sense, the system adds up the number of photons it receives.
21. Partnership Timing
1.These categories were: (0) extremely early; (1) moderately early; (2) slightly early; (3) intermediate; (4) slightly late; (5) moderately late; (6) extremely late.
2.We took only those subjects who had assessed their partners, which left us with just over 20,000 women (represented here as circles) and just under 20,000 men (squares). The horizontal axes represent the subjects’ chronotypes based on the midsleep on free days (MSF) and the vertical axes represent the average values of the seven chronotype categories, from 0 (extremely early) to 6 (extremely late). For comparison, the distribution of chronotypes in the entire database is shown on the graph as gray bars.
3.The reason for this difference is presumably due to Indians being exposed to much more light and therefore much stronger zeitgebers than Central Europeans.
4.We did this by looking at different age groups (20 to 24, 25 to 29, 30 to 34, and so on) and calculating the average difference between the seven category–based assessment of self and of partner. Since we were only interested in how discrepant these two assessments were, we took the absolute difference (again separately for men and women). So an individual who categorizes his or her chronotype to be 2 (slightly early) and that of the partner as either 1 (moderately early) or 3 (intermediate) would both yield an absolute difference of 1.
5.As opposed to a longitudinal study, which accompanies subjects over a longer time span and can thus report the real changes that occur with age.
22. A Clock for All Seasons
1.Tom Wehr used to work at the National Institute of Mental Health in Bethesda, Ma
ryland, until he retired as an emeritus a couple of years ago (in my view, much too early—he had contributed so many lovely experiments to the field of human clock and sleep research).
2.The title of an earlier chapter, “Wait until Dark,” is from the film in which Audrey Hepburn plays a blind woman who removes all light bulbs in her apartment to have an advantage over a sighted murderer. Her strategy works perfectly until the murderer hears the refrigerator go on and immediately makes his way through the dark room to open its door.
3.For examples of Wehr’s work, see T. A. Wehr, D. Aeschbach, and W. C. Duncan (2001). Evidence for a biological dawn and dusk in the human circadian timing system. Journal of Physiology 535:937–951; or T. A. Wehr (1996). A “clock for all seasons” in the human brain. Progress in Brain Research 111:321–342. In my chapter “Wait until Dark,” the clan’s storyteller speculates on the state between sleep and wakefulness.
4.I collected data such as maximum and minimum daily temperatures, hours of sunshine, amount of rain, humidity, and many others. I also calculated for each location the annual changes in photoperiod. The light part of the day from sunrise to sunset is called photoperiod; the corresponding dark part is called scotoperiod.
5.Our preference for eating food with more protein content during the summer and more carbohydrate content during the winter probably has a biological basis, going back to the days when we needed more nutritional fuel to burn during the cold winter months. It seems likely that the annual Christmas-cookie binge may be a tradition based more in biology than culture.
6.The longest day of the year is June 22 in the northern hemisphere and December 22 in the southern hemisphere.
7.This depression is different from its seasonal variant. Patients cycle through alternations between depression and mania (almost the opposite of depression); the period of this cycling is much shorter than twelve months.
8.Think of Gerry and Barbara: “When spring finally came, they experienced a hitherto unknown surge of fresh energy. One morning, looking at the trees outside, Gerry mused that he now knew what it must feel like to shoot leaves.”
Internal Time: Chronotypes, Social Jet Lag, and Why You’re So Tired Page 24
