4.1 Notes: Circadian Rhythms and Sleep (Pages 1–8)

Page 1

  • Learning Objectives: By the end of this section, you will be able to:
    • Understand what is meant by consciousness.
    • Explain how circadian rhythms regulate the sleep-wake cycle and how these cycles can be disrupted.
    • Discuss the concept of sleep debt.
  • Consciousness:
    • Consciousness describes our awareness of internal and external stimuli.
    • Internal stimuli: feeling pain, hunger, thirst, sleepiness, and being aware of thoughts and emotions.
    • External stimuli: seeing sunlight, feeling warmth, hearing a voice.
    • We experience different states of consciousness and different levels of awareness regularly.
    • Consciousness can be viewed as a continuum from full awareness to deep sleep.
  • Sleep and wakefulness:
    • Sleep is a state with relatively low physical activity and reduced sensory awareness, distinct from rest during wakefulness.
    • Wakefulness involves high levels of sensory awareness, thought, and behavior.
    • Beyond wakefulness and sleep, there are states like daydreaming, intoxication, and unconsciousness due to anesthesia.
    • Even when fully awake, we are often not completely aware of surroundings (e.g., daydreaming while driving).
  • Biology of behavior:
    • Many processes, including psychological behavior, are rooted in biology.
  • Biological Rhythms:
    • Biological rhythms are internal rhythms of biological activity.
    • Example: a woman’s menstrual cycle is a biological rhythm—recurring, cyclic bodily changes.
    • One complete menstrual cycle takes about 28 days28\text{ days}, though many biological cycles are shorter.
    • Body temperature fluctuates cyclically over a 24-hour24\text{-hour} period; alertness tends to be higher when body temperature is higher, and sleepiness when it is lower.
  • Key concept: circadian rhythms often tie to environmental cues and physiological states.

Page 2

  • Figure 4.2 (descriptive content): circadian change in body temperature over 28 hours28\text{ hours} in a group of eight young men.
    • Body temperature rises during the waking day, peaks in the afternoon, and falls during sleep with the lowest point in the very early morning.
    • This daily fluctuation is an example of a circadian rhythm: a biological rhythm that takes place over about 24 hours24\text{ hours}.
  • Sleep-wake cycle:
    • Our sleep-wake cycle is linked to the environment’s natural light-dark cycle.
    • We also have daily fluctuations in heart rate, blood pressure, blood sugar, and body temperature.
  • Circadian clock in the brain:
    • The hypothalamus, above the pituitary, is a main center of homeostasis.
    • The brain’s clock mechanism is located in the suprachiasmatic nucleus (SCN).
    • Light-sensitive retinal axons provide information to the SCN about environmental light levels, synchronizing the internal clock with the outside world. (Klein, Moore, & Reppert, 1991; Welsh, Takahashi, & Kay, 2010)
  • Figure 4.3 (caption): The SCN serves as the brain’s clock mechanism. The clock sets itself with light information received through projections from the retina.

Page 3

  • Problems With Circadian Rhythms (overview):
    • For most people, circadian cycles align with the outside world (e.g., sleeping at night, being awake during the day).
    • Melatonin is a key regulator of the sleep-wake cycle.
    • The pineal gland releases melatonin and is involved in regulating various biological rhythms and the immune system during sleep (Hardeland, Pandi-Perumal, & Cardinali, 2006).
    • Melatonin release is stimulated by darkness and inhibited by light.
    • Individual differences in circadian patterns are known as chronotypes (e.g., morning larks vs night owls) (Taillard, Philip, Coste, Sagaspe, & Bioulac, 2003).
    • Sleep regulation refers to the brain’s control of switching between sleep and wakefulness and coordinating this cycle with the outside world.
  • Link to learning: (Content directs to further resources in the chapter.)

Page 4

  • Disruptions of Normal Sleep:
    • Circadian clock disruptions can occur when traveling across multiple time zones (jet lag) or with rotating shift work.
    • Jet lag: mismatch between internal circadian cycles and environment; symptoms include fatigue, sluggishness, irritability, and insomnia (defined as difficulty falling or staying asleep for at least three nights a week over a month) (Roth, 2007).
    • Rotating shift work: schedules that change from early to late shifts daily or weekly (e.g., 7:00–15:00, then 03:00–11:00, then 11:00–19:00).
    • Frequent schedule changes prevent a normal circadian rhythm, often resulting in sleep problems and symptoms of depression and anxiety.
    • Qualitative study of middle-aged nurses on rotating shifts highlighted impacts on family relationships and exhaustion (West, Boughton & Byrnes, 2009).
    • Practical implications: disruptions can affect safety, performance, and well-being in health care and service industries.
  • Mitigation ideas (intro to learning): realignment strategies exist, such as light exposure timing and other circadian-aligned practices. (LINK TO LEARNING)

Page 5

  • Realigning circadian rhythms:
    • Exposure to bright light helps realign the clock; light drives the biological clock.
    • Bright light exposure during work shifts and darkness when not working can combat insomnia and symptoms of anxiety and depression (Huang, Tsai, Chen, & Hsu, 2013).
  • Devices and interventions:
    • Devices designed to provide bright light exposure can help maintain a regular circadian cycle, useful for night-shift workers and people affected by seasonal variations in light.
  • Practical takeaway: light acts as a primary zeitgeber (time cue) for circadian alignment.

Page 6

  • Insufficient Sleep / Sleep Debt:
    • When sleep is regularly insufficient, a person accumulates a sleep debt, leading to decreased alertness and mental efficiency.
    • Since electric lighting became common, total sleep has declined; more activity during nighttime leads to reduced sleep relative to ancestral patterns.
    • Sleep needs vary by age. The National Sleep Foundation (n.d.) suggests newborns require the most sleep (between 12 and 18 hours12\text{ and }18\text{ hours} per day) and that this declines to about 7–9 hours7\text{–}9\text{ hours} in adulthood.
    • In 2015, the National Sleep Foundation updated sleep duration recommendations to better account for individual differences.
    • Table 4.1: Sleep needs at different ages (sampled values in the chapter):
  • Table 4.1 (Sleep Needs at Different Ages):
    • Age
    • Recommended
    • May be appropriate
    • Not recommended
    • 0–3 months: 14–17 hours14\text{–}17\text{ hours}; 11–13 hours11\text{–}13\text{ hours}; 18–19 hours18\text{–}19\text{ hours}; Fewer than 11 hours11\text{ hours}; More than 19 hours19\text{ hours}
    • 4–11 months: 12–15 hours12\text{–}15\text{ hours}; 10–11 hours10\text{–}11\text{ hours}; 16–18 hours; Fewer than 10 hours; More than 18 hours
    • 1–2 years: 11–14 hours11\text{–}14\text{ hours}; 9\–10\text{ hours}; 15–16 hours; Fewer than 9 hours; More than 16 hours
    • 3–5 years: 10–13 hours10\text{–}13\text{ hours}; 8\–9\text{ hours}; 14 hours; Fewer than 8 hours; More than 14 hours
    • 6–13 years: 9\–11\text{ hours}; 7\–8\text{ hours}; 12 hours; Fewer than 7 hours; More than 12 hours
    • 14–17 years: 8\–10\text{ hours}; 7 hours7\text{ hours}; 11 hours; Fewer than 7 hours; More than 11 hours
    • 18–25 years: 7\–9\text{ hours}; 6 hours6\text{ hours}; 10–11 hours; Fewer than 6 hours; More than 11 hours
    • 26–64 years: 7\–9\text{ hours}; 6 hours6\text{ hours}; 10 hours; Fewer than 6 hours; More than 10 hours
    • ≥65 years: 7\–8\text{ hours}; 5\–6\text{ hours}; 9 hours; Fewer than 5 hours; More than 9 hours
  • Notes:
    • Sleep debt and sleep deprivation have significant negative psychological and physiological consequences. (Figure 4.5.)
    • The table and notes emphasize variability and the idea that “recommended” ranges are guidelines, not rigid rules.

Page 7

  • Sleep debt and deprivation effects:
    • Lack of sleep leads to negative psychological and physiological consequences, including depression-like symptoms and impaired cognitive function.
    • Sleep deprivation is associated with obesity, increased blood pressure, higher stress hormone levels, and reduced immune functioning (Banks & Dinges, 2007).
    • A sleep-deprived individual generally falls asleep more quickly than when not sleep-deprived.
    • Some sleep-deprived individuals have difficulty staying awake when sedentary (e.g., watching TV or driving).
    • Sleep deprivation can impair cognitive and motor function, potentially as much as or more than alcohol intoxication (Killgore & Weber, 2014; Killgore et al., 2007).
    • The most severe effects occur after staying awake for more than 24 hours, or after repeated nights with fewer than four hours in bed (Wickens, Hutchins, Lauk, Seebook, 2015). Irritability, distractibility, and impairments in cognitive and moral judgment can occur with fewer than four hours of sleep.
  • Sleep deprivation can lead to perceptual disturbances, including hallucinations after extended wakefulness (e.g., 48 hours).
  • Figure 4.5 (caption): This figure illustrates some negative consequences of sleep deprivation. (Credit: modification of work by Mikael Häggström)
  • Lifespan considerations: The amount of sleep needed varies across the lifespan; newborns sleep up to ~16 hours, decreasing with age. A meta-analysis (Ohayon, Carskadon, Guilleminault, & Vitiello, 2004) indicates by age 65, the average sleep is fewer than 7 hours7\text{ hours} per day.
  • Readings and resources: The chapter suggests reading articles about sleep needs to assess personal sleep habits.

Page 8

  • Sleep needs across the lifespan continue to show variability and gradual reduction with age.
  • Quantitative summary: By age 65, many individuals average less than 7 hours7\text{ hours} of sleep per day (Ohayon et al., 2004).
  • Modern lifestyle and sleep: The chapter notes ongoing research into sleep duration trends and the impact of artificial lighting and modern schedules on sleep health.
  • Additional learning: A brief video on overcoming jet lag is referenced to provide practical tips.
  • Practical implications:
    • Sleep needs are personal and context-dependent; planning around circadian rhythms and sleep debt can improve alertness, mood, and safety.
    • Healthcare and service professions are particularly affected by circadian disruptions; management strategies include light exposure, scheduling considerations, and sleep hygiene practices.
  • Summary of links:
    • Circadian rhythm theory links to real-world issues like jet lag, shift work, and modern lighting.
    • Sleep debt connects to daytime functioning, mental health, and long-term health outcomes.
  • Key formulas and numbers to remember:
    • Circadian period: ≈24 hours\approx 24\text{ hours}
    • Body temperature fluctuation period: ≈24 hours\approx 24\text{ hours} (Figure 4.2)
    • Newborn sleep need (example): 12–18 hours12\text{–}18\text{ hours} per day
    • Adult sleep need (example): 7–9 hours7\text{–}9\text{ hours} per night
    • 65+ sleep average (example): <7\text{ hours} per night (Ohayon et al., 2004)