Psychology
Sleep and Zeitgebers
Sleep is regulated by internal biological clocks known as circadian rhythms, which are synchronized with external cues called zeitgebers. Zeitgebers, such as light and social cues, help to regulate the sleep-wake cycle by signaling the body's internal clock. Disruptions to these zeitgebers, such as jet lag or shift work, can lead to sleep disturbances and impact overall well-being.
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11 Key excerpts on "Sleep and Zeitgebers"
eBook - PDFSleep Disorders
Diagnosis and Therapeutics
- S. R. Pandi-Perumal, Joris Verster, Jaime Monti, Salomon Langer, S. R. Pandi-Perumal, Joris Verster, Jaime Monti, Salomon Langer(Authors)
- 2008(Publication Date)
- CRC Press(Publisher)
Zeitgebers adjust or ‘entrain’ the body clock to the zeitgeber period. In dif-ferent mammals, rhythms of the light–dark cycle, of food availability–unavailability, of activity–inactivity, and of social influences act, singly or in combination, as zeitgebers. In humans also, some combination of these influences is normally present. Nevetheless, in practice, the most important zeitgeber in humans is the light–dark cycle, combined with the rhythm of melatonin secretion. Other possible zeitgebers – including exercise, social factors, and food intake – appear to play a minor role only. 36–42 Light The effect of light upon the body clock depends on the time of presentation, and the time of the temper-ature minimum (normally around 05:00 h) is an important marker for these effects. Light in the 6 hours after this minimum advances the body clock, in TIME-ZONE TRAVEL, JET LAG, AND SLEEP DISTURBANCES 469 the 6 hours before, delays it, and at other times exerts no effect upon the clock (although it causes a general mental activation at whatever time it is presented). This non-parametric relationship between the time of light exposure and the phase shift that it produces in the body clock is called a phase response curve (PRC). 43– 45 The size of the phase shift produced depends upon the intensity of the light, with domestic lighting exert-ing a smaller effect than natural lighting. Even so, in the many individuals who nowadays have very little exposure to natural daylight, domestic lighting is suf-ficient to entrain the circadian clock to a 24-hour rhythm. 46–49 Light information passes directly from the retina to the SCN via the retinohypothalamic tract. The origin of this input is thought to be hori-zontal cells containing a pigment that is based on vit-amin B 2 rather than the rods and cones and their vitamin A 1 -based opsins. 50 Melatonin Melatonin ingestion also adjusts the phase of the body clock.
eBook - PDFDiscovering Behavioral Neuroscience
An Introduction to Biological Psychology
- Laura Freberg(Author)
- 2018(Publication Date)
- Cengage Learning EMEA(Publisher)
Due to electronic rights, some third party content may be suppressed from the eBook and/or eChapter(s). Editorial review has deemed that any suppressed content does not materially affect the overall learning experience. Cengage Learning reserves the right to remove additional content at any time if subsequent rights restrictions require it. CHAPTER 11 Sleep and Waking 376 Biorhythms Seasonal migrations, mating seasons, and the human menstrual cycle are just a few examples of behaviors that occur at regular intervals in response to internal, biological clocks. Our focus in this chapter is on the rhythms associated with sleep and waking (see ● Figure 11.1). Together, the interplay of sleep and waking cycles follow circadian, or daily, rhythms. The term circadian comes from the Latin words for “about a day.” In addition, regular cycles of relative activation and quiet occur about every 90 to 120 minutes within the 24-hour day. These ultradian cycles are shown in ● Figure 11.2. To establish and maintain these rhythms, internal biological clocks interact with stimuli known as zeitgebers. ( Zeit means “time” in German; geber means “to give”; hence, these are “time givers.”) Light is the most important zeitgeber for human beings. In the absence of natural light, human free-running circadian rhythms last approx-imately 24.2 hours to 24.9 hours (Czeisler & Gooley, 2007; Sack, Brandes, Kendall, & Lewy, 2000). Exposure to sunlight each day helps reset, or entrain, the internal biologi-cal clock to the 24-hour cycle of the earth’s rotation. Totally blind people and sailors on submarines experience free-running cycles that are longer than 24 hours, often resulting in severe sleep disruptions (Kelly et al., 1999; Skene, Lockley, Thapan, & Arendt, 1999). In addition to light, other zeitgebers include physical activity, feeding, body tem-perature, and sleep-related hormones discussed later in this chapter (Van Someren & Riemersma-Van Der Lek, 2007; Whalley, 2013).
eBook - PDF- James Kalat(Author)
- 2018(Publication Date)
- Cengage Learning EMEA(Publisher)
By Monday morning, when the clock on your table indicates 7 a.m., your biological clock may say 5 a.m., and you stagger off to work or school without much pep (Moore-Ede, Czeisler, & Richardson, 1983). Although circadian rhythms persist without light, your rhythm is not perfect. Unless something resets it from time to time, it would gradually drift away from the correct time. The stimulus that resets the circadian rhythm is referred to by the German term zeitgeber (TSITE-gay-ber), meaning “time-giver.” Light is by far the dominant zeitgeber for land animals (Rusak & Zucker, 1979), whereas the tides are important for some marine animals. In addition to light, other zeitgebers include exercise (Eastman, Hoese, Youngstedt, & Liu, 1995), arousal of any kind (Gritton, Sutton, Martinez, Sarter, & Lee, 2009), meals, and the temperature of the environment (Refinetti, 2000). Social stimuli—that is, the effects of other people—are ineffective as zeitgebers, unless they induce exercise or other vigorous ac-tivity (Mistlberger & Skene, 2004). Although these additional zeitgebers modify the effects of light, they have only weak ef-fects on their own. For example, people who are working in Antarctica during the constant darkness of an Antarctic winter try to maintain a 24-hour rhythm, but they drift away from it. Different people generate slightly different rhythms, until they find it more and more difficult to work together (Kennaway & Van Dorp, 1991). Astronauts in orbit face a special problem: As they orbit the Earth, a 45-minute period of daylight alternates Copyright 2019 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. Due to electronic rights, some third party content may be suppressed from the eBook and/or eChapter(s). Editorial review has deemed that any suppressed content does not materially affect the overall learning experience.
eBook - ePub- Amanda Ellison(Author)
- 2012(Publication Date)
- Bloomsbury Academic(Publisher)
9 Just sleep on itOur lives are ruled by rhythm, and I’m not talking about “Dad dancing at weddings” rhythm here. These rhythms take the form of cycles, peaks and troughs of activity throughout the day, month or even year. In the natural world the tide goes in and out every day. Women have a monthly menstrual cycle up until the menopause (menopausal men buy motorcycles). The sleep/wake cycle is generally thought to be our most important daily cycle, and is known as a circadian rhythm. This is the rhythm that gets disrupted if you fly to another time-zone, particularly if you fly east. When everybody is ready for bed, you may be in the middle of the afternoon in your cycle and it takes time to adjust. Our sleep/wake cycle is very constrained to the day/night cycle of the sun and indeed light does control this circadian rhythm. Zeitgebers (meaning time-givers) are environmental events that entrain biological rhythms and light from the sun is our most important Zeitgeber. But what would happen if we lived in a nuclear bunker and we had no light cues at all? What would happen to our biorhythms then?It turns out that in the absence of external environmental cues, we have a perfectly functioning biorhythm, but our sleep/wake cycle would last for 26 hours and not the 24 that we usually have to match the day/night cycle. This endogenous circadian clock seems to be located in the suprachiasmatic nucleus (SCN) of the hypothalamus. If the SCN is disconnected from the rest of the brain, its neurons continue to show fluctuations of neuronal activity that match the circadian rhythm. Damage to the SCN causes animals to continue to eat, drink, exercise and sleep but they do so at haphazard times and so the SCN is not just a biological clock but acts as a pacemaker for other rhythms too. The location of the SCN (see Figure 9.1 ) also explains how light can entrain our endogenous rhythm as it receives direct input from the retina (the retino-hypothalamic pathway mentioned in Chapter 4
eBook - PDF- Jon C. Horvitz, Barry L. Jacobs(Authors)
- 2022(Publication Date)
- Cambridge University Press(Publisher)
Some genetic evi- dence suggests that these characteristics may run in families. 5.2 STAGES OF SLEEP 197 The study of circadian rhythms also helps us to understand jet lag. Say that your flight departs New York City at 8:00 p.m. and lands in Rome at 8:00 a.m. local time on the following day. In your excitement, you want to rush out immediately to see the Coliseum. However, it’s still only 2:00 a.m. in New York. With your sleep–wake cycle still entrained to New York zeitgebers, your biological clock tells you that you should be in bed. Expo- sure to the bright Roman morning sunshine will cause your internal clock to reset in a few days, i.e., your sleep–wake cycle will eventually entrain to the time cues in Rome. KEY CONCEPTS • Virtually all life on earth is influenced by a circadian cycle of approxi- mately 24 hours. • While typically influenced by external cues such as periods of light and darkness, a biological clock operates in the absence of any external signals. • In mammals, the brain mechanism controlling circadian rhythms is located in the suprachiasmatic nucleus of the hypothalamus. • The degree to which you feel tired depends on an interaction between your biological clock and how long you have been awake. TEST YOURSELF 1. If you were in a cave with no external cues about time of day, would you still show a circadian rhythm? Would you begin to sleep at random times during the day and night? 2. What brain structure is considered the brain’s master clock? 3. Sleep is said to be governed by circadian and homeostatic factors. Ex- plain what this means. 4. After a night without sleep, a person may be very tired at 4:00 a.m. Surprisingly, they may feel less tired at 9:00 a.m., even though they have had 5 additional hours without sleep! Why? 5.2 STAGES OF SLEEP In the sleep laboratory, researchers employ several physiological meas- ures as the individual sleeps. Three key measures are examination of brain waves, muscle activity, and eye movements.
eBook - ePub- Richard B. Berry, Mary H. Wagner, Mary H Wagner(Authors)
- 2014(Publication Date)
- Saunders(Publisher)
The period of the rhythm is called tau and the mean value in humans is about 24.2 hours. 3 For humans to maintain synchrony with the light–dark cycle, external stimuli must induce a slight daily advance (shift in circadian rhythms to an earlier clock time) to counteract the intrinsic tendency for phase delay caused by a period slightly longer than 24 hours. These external stimuli, called zeitgebers (“time givers”), are said to “entrain” the SCN to the light–dark cycle (Box F40-1). Box F40-1 Circadian Physiology—Important Facts • Circadian (“about a day”) denotes processes with approximately a 24-hour (hr) period. • The human period of circadian rhythms (tau) is about 24.2 hr. • The suprachiasmatic nucleus (SCN) is the major circadian pacemaker in humans. • The SCN function helps maintain alertness by producing an alerting signal during the day and maintaining sleep by a reduced signal at night. • Human alertness: • Midday decrease in alertness 2–4 pm. • Alertness peaks in the early evening hours. • Lowest levels of alertness occur from 4–6 am. • Zeitgebers (time givers) entrain the SCN to the physical environment. • Light (sunlight) is the major zeitgeber. • Melanopsin-containing retinal ganglion cells are the major circadian photoreceptors and communicate the presence of light to the SCN via the retinohypopthalamic tract (RHT). The most potent zeitgeber is light (sunlight). Other zeitgebers include exercise, food, and social activities. The light stimulus reaches the SCN via the retinohypothalamic tract (RHT) (Figure F40-1). The RHT is a monosynaptic pathway connecting the melanopsin-containing photosensitive retinal ganglion cells (pRGCs) to the SCN. The neurotransmitters of the RHT are glutamate and pituitary adenylate cyclase activating polypeptide (PACAP)
eBook - PDFTime and Behaviour
Psychological and Neurobehavioural Analyses
- C.M. Bradshaw, E. Szabadi(Authors)
- 1997(Publication Date)
- North Holland(Publisher)
The degree of precision with which the underlying clock is expressed behaviorally, for example in sleep/wake or rest/activity patterns, is dependent largely on the degree of environmental structure within which it functions. In studies such as the one just described, in which subjects are permitted to sleep anytime throughout the circadian day, they do exactly as instructed. That is, sleep can, and does, occur at all phases of the circadian day, as illustrated in Figure 1. Under circumstances in which even fewer behavioral options are permitted, such as the bed rest design, or the disentrainment protocol, sleep and waking episodes become even more labile, rendering the circadian organization of behavior almost unrecognizable as such (see for example Campbell, 1984; Campbell & Zulley, 1985). Yet, even under the most unstructured behavioral conditions, careful examination of certain physiological components of these behavioral variables reveals the continuing influence of the endogenous circadian pacemaker. For example, the proportions of both REM sleep and slow wave sleep comprising a given sleep episode are dependent on the time at which that sleep bout occurs. Likewise, as illustrated in Figure 1, the duration of a sleep episode is not only determined by whether a subject perceives the sleep to be a nap or a major sleep episode, but is also dependent on the circadian phase at which the sleep bout occurs (Czeisler, Weitzman, Moore-Ede, Zimmerman, & Knauer, 1980; Zulley, 1980; Zulley, Wever, & Aschoff, 1981). Long-Term Time Estimation in Humans 389 12 ~,._ 10t o 8- c .o_ 6- 121 L.- . 1 1 1 1 I I I I I I I 1 I I I 1 I 1 1 ~ 1 I I I 1 I I I t I I 1 I I I I I I i I l 1 1 1 I 1 1 ~ 0 5 10 15 20 25/0 5 10 15 20 25/0 time from minimum of body temperature (hours) Figure 1. Average durations of sleep periods as a function of the circadian phase of onset, obtained from six subjects while living in a time-free environment (Zulley & Campbell, 1985).
eBook - PDF- Thomas Brown(Author)
- 2012(Publication Date)
- Academic Press(Publisher)
But studies in which the day/night cycle are altered, or in which individu-als have no cues to tell them when it is dark or light outside, suggest that an internal clock (or clocks) exists. Several studies have been conducted on human beings in environments which are essentially free of time cues. These studies all suggest that a rhythm is maintained under these conditions, but it differs in some respects from the normal circadian rhythm. Webb and Agnew (1974a), for example, stud-ied seven male subjects, aged 18-29 years old. These volunteers were kept isolated between 10 and 14 days in rooms designed to eliminate all cues to the time of day. The sound levels were kept constant by an air conditioner and the subjects could request food through a communication system anytime during the experiment. To counteract the effects of boredom, each room was equipped with books and a stereo system; it was also Figure 13.7 Sleep wakefulness patterns of eight subjects in an environment free of cues to time of day. Upper graphs are for subjects who did not exercise strenuously, lower graphs are for subjects who did. [From Webb and Agnew (1974a).] l a l b l e l g 372 physiological psychology equipped with microphones and a closed-circuit TV in order to monitor the subject. Figure 13.7 shows the sleeping-waking patterns for several sub-jects during the experiment. The lines across each day represent when the subject slept. Subject la showed a typical pattern: each day he went to bed slightly later than the day before, and also slept later. The patterns for the other subjects were essentially the same, although slightly more irregular. Subject lm's pattern was such that by the end of the first week he was sleeping during the actual daytime and stay-ing awake during the night. Subject In showed a similar, but more erratic pattern.
eBook - ePubSleep Difficulties and Autism Spectrum Disorders
A Guide for Parents and Professionals
- Kenneth Aitken(Author)
- 2012(Publication Date)
- Jessica Kingsley Publishers(Publisher)
The similarities in the underpinning biological processes, across the animal kingdom, are allowing significant developments in our understanding of human sleep to be made through the study of its development in other ‘model organisms’ such as Drosophila melanogaster (the fruit fly) and Danio rerio (the zebrafish) (Hendricks, Sehgal and Pack 2000). In addition to sleep–wake cycle issues, mood disorders including unipolar depression and seasonal affective disorder are typically due to abnormalities of the circadian system (McClung 2007; Monteleone and Maj 2008). There is a growing body of evidence that circadian abnormalities are seen in a large proportion of individuals with ASDs (Glickman 2010). Methods for the reliable assessment of human circadian rhythms are now available and in use (see Hofstra and de Weerd 2008). Variations in cognitive ability follow a circadian pattern and are affected both by endogenous circadian clocks and external factors that vary the amount and timing of actual sleep (Kyriacou and Hastings 2010). W HAT IS SLEEP? A useful starting point in understanding and unravelling sleep problems is trying to get a basic idea of what sleep is, why we might do it and what it might be for. We should start by defining what we mean by sleep. There are many definitions to choose from. Here is a selection: Sleep is a reversible condition of reduced responsiveness usually associated with immobility. (Cirelli and Tononi 2008, p.1605) …sleep is that golden chain that ties health and our bodies together. (Thomas Dekker, The Gull’s Hornbook 1609) Sleep is the interest we have to pay on the capital which is called in at death; and the higher the rate of interest and the more regularly it is paid, the further the date of redemption is postponed. (Arthur Schopenhauer) Sleep that knits up the ravelled sleave of care, the death of each day’s life, sore labour’s bath, balm of hurt minds, great nature’s second course, chief nourisher in life’s feast
- John Weinman(Author)
- 2013(Publication Date)
- Butterworth-Heinemann(Publisher)
Finally, it should be noted again that although circadian variations in psychological processes can be demonstrated these do not necessarily have an absolute effect in that they can be modified by social, motivational and personality factors. • 4.3. Sleep The most obvious behavioural change which occurs during the circadian cycle is the transition from wakefulness to sleep. For most of us approximately one-third of the 24-hour period is spent in sleep and so a separate consideration of its nature seems appropriate. Moreover, sleep disorders are among the commonest symptoms seen by doctors and to some extent these can be understood more easily with reference to the 'normal' pattern of sleep. a. What is sleep? It is probably not too surprising to find that sleep occurs at a time in the circadian cycle when body temperature and arousal level are at their lowest. A common-sense interpretation of the functions of sleep would therefore be in terms of a recovery process in response to the activities of the preceding day and as a preparation for a new day. However, the notion of sleep as the natural response to a hard day's activity can be seen to be too limited since the amount of sleep may be relatively unaffected by the variability in waking levels of activity. It seems as if sleep constitutes a very basic part of the overall circadian pattern which is laid down in the early period of development and persists throughout life. One further misconception about sleep is that it is a somewhat passive state and corresponds to an absence of wakefulness and mental activity. It is now known that there are 47 Arousal, circadian rhythms and sleep brain regions which give rise to cortical rhythms associated with the onset and maintenance of sleep. Sleep is by its very nature a private event and relatively inaccessible to research investigation. In general terms, sleep is indicated by loss of awareness and a decreased responsiveness to the environment.
eBook - PDFMotivation and Emotion
Evolutionary, Physiological, Cognitive, and Social Influences
- David C. Edwards(Author)
- 1998(Publication Date)
- SAGE Publications, Inc(Publisher)
The time cues, or Zeitgebers (time-givers in German) entrain (cue, drag, or carry along) the rhythm functions. Change in daily activity routine can also disrupt body rhythms. Traveling to a different time zone and changing the time of one's work to a new shift are alterations in Zeitgebers that may de-synchronize circadian biological rhythms. The practical questions are how and how soon will one become entrained to a specific new time environment. Travel to a different time zone affects body functions and performances, but a com-plete picture is not yet ready. The first rush of findings produced a long list of potential dis-abilities from a single large change in time zone. Heading the list of jet-lag symptoms were sleep disturbance, fatigue, and slow mental performance. Frequent time-zone travelers reported headaches, burning eyes, digestion upset, unprovoked sweating, men-strual irregularities, and possibly premature aging (Luce, 1971). These studies of aviation professionals also introduced the problem of separating time-zone changes from symp-toms of work stress, including irregular rest periods. Among the most predictable effects and perhaps the dominant factor of time-zone change is sleep disturbance. Change in timing breaks the laws of sleep. A traveler is either awake at the time of normal sleep or expected to sleep after too short a period of being awake. The effects are those of being sleepy at inappropriate times and difficulty getting sufficient sleep when the social schedule in the new time zone dictates. Together these ef-fects lead to feelings of sleepiness and fa-tigue, perhaps partly the cause of subnormal mental performance. The practical questions are how to deal with time-zone, activity-rest disruptions, and how long does it take to adapt to the changed time. Some partial answers are available. There are differences in adaptation to time-zone change depending upon the direction of the change.
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