Introduction to Behavioral Neuroscience: Biological Rhythms and Sleep

Introduction to Behavioral Neuroscience: Biological Rhythms and Sleep

  • Introduction
      - This chapter is provided by OpenStax and licensed under a CC BY-NC-SA 4.0 International license. Adaptations must retain attribution to OpenStax, Rice University and must be shared under similar terms.

Attributions

  • Authors: Megan M. Mahoney, PhD and Eric M. Mintz, PhD
  • Slides Prepared by: Elizabeth D. Kirby

Chapter Outline

  • 15.1 What are circadian rhythms?
  • 15.2 Where are rhythms in the brain?
  • 15.3 Regulation of sleep
  • 15.4 Disorders of sleep and circadian rhythms
  • 15.5 Circadian rhythms and society

15.1 What are Circadian Rhythms?

  • Chronobiology: The study of biological clocks and biological rhythms within an organism. This includes:
      - Cycles of gene transcription
      - Hormone surges
      - Patterns of fatigue and alertness

Types of Biological Rhythms

  • Circadian: ~24 hours
      - Example: Sleep-wake cycle
  • Ultradian: <24 hours
      - Example: Ocean tides
  • Infradian: >24 hours
      - Example: Cycles of moonlight
  • Circannual: ~1 year
      - Example: Hibernation

Components of Biological Rhythms

  • Rhythm: A repeating event that occurs with a regular pattern
  • Level: Includes gene expression, activity, hormones, etc.
  • Period: The length of a full cycle
  • Amplitude: The strength or magnitude of the rhythm
  • Phase: The timing within the cycle

Characteristics of Biological Rhythms

  • Endogenous: Humans and animals display a ~24-hour activity-rest/sleep cycle even under constant dim light or darkness. This is referred to as the free-running period.
  • Entrainable: Human free-running period ranges from 23.5 to 24.7 hours/day, which can synchronize with external environmental cues.

Chronotypes

  • Refers to the tendencies of individuals towards sleeping during certain times of the day and being more alert at others.
      - Examples: Night owls vs. early birds

Photic Phase Response Curve

  • The study of circadian rhythms in laboratory settings, such as observing rodent wheel running behavior which increases at night when rodents are most active.
  • Under constant darkness, these rodents maintain a 24-hour activity rhythm.

15.2 Where are Rhythms in the Brain?

The Suprachiasmatic Nucleus (SCN)

  • The SCN is identified as the master clock located in the hypothalamus.

Lesion Experiments

  1. An intact hamster shows a 24-hour rhythm.
  2. Lesioning the SCN causes the hamster to exhibit arrhythmic activity.
  3. Transplanting fetal SCN tissue restores the hamster's free-running rhythm but does not allow it to entrain to light.

Input from the Retina

  1. Blue wavelength light activates intrinsically photosensitive retinal ganglion cells (ipRGCs).
  2. ipRGC axons form the retinohypothalamic tract, exciting the SCN.

Outputs from the SCN

  • Regulates processes such as:
      - Body temperature
      - Locomotor activity
      - Sleep-wake cycle
      - Hormone release

Clock Genes: Endogenous Gene Expression Cycle

  1. CLOCK and BMAL1 proteins induce the expression of per and cry genes by binding to their promoters.
  2. PER and CRY proteins accumulate in the cytoplasm.
  3. PER and CRY enter the nucleus, inhibiting CLOCK and BMAL1 from binding to DNA, blocking their expression.
  4. As PER and CRY degrade, CLOCK and BMAL1 can re-bind, restarting the cycle.

Connection to Pineal Gland and Melatonin

  1. Light activates ipRGCs which excite SCN neurons.
  2. SCN cells project to spinal cord neurons inhibiting the pineal gland.
  3. Activation of SCN reduces melatonin secretion while inhibition of the SCN corresponds with increased melatonin release.

Melatonin as a Medical Treatment

  • Melatonin is used to treat conditions such as:
      - Insomnia
      - Jet lag
      - Circadian rhythm and shift work sleep disorders
      - Improve sleep quality in the elderly

Test-like Question

  • Question: Where would damage result in a disturbed ability to maintain circadian rhythm of melatonin?
      - a) Visual cortex
      - b) Optic nerve
      - c) Suprachiasmatic nucleus
      - d) A and C
      - e) B and C

15.3 Regulation of Sleep

Factors that Drive Sleep

  • Process C: Circadian rhythm
  • Process S: Homeostatic pressure

Why Do We Need Sleep?

  • Restoration of physical and mental energy
  • Protection from predators
  • Support plasticity for learning
  • Reduced energy demand
  • Support of growth and development

How Do We Measure Sleep?

  • Polysomnography: A combination of technologies that measure
      - Brain waves (EEG)
      - Eye movements (EOG)
      - Muscle movements (EMG)

Hypnogram: Sleep Stages

  • Non-REM (NREM) sleep is more prevalent early in the sleep period.
  • REM sleep occurs predominantly in the last half of sleep.

Brain Circuits Regulating Sleep

  • Ascending wake-promoting brain regions and pathways originate from brainstem nuclei and extend throughout the forebrain.

Sleep Regulation via the Flip Flop Switch

  • Sleep transitions are regulated by a flip flop switch where wake and sleep promoting regions inhibit each other.
      - Waking: Affected by histamine (TMN), serotonin (Raphe nuclei), and norepinephrine (Locus coeruleus)
      - Sleeping: Affected by GABA and galanin (VLPO; Ventrolateral Preoptic Nucleus).

15.4 Disorders of Sleep and Circadian Rhythms

Common Sleep Problems

  • Inadequate sleep duration
  • Fragmented sleep periods
  • Sleepiness at inappropriate times
  • Inability to fall asleep at desired times

Non-24-hour Sleep/Wake Disorder

  • Occurs when the internal clock is not synchronized to external cues.
      - Example cause: Retina damage

Narcolepsy

  • Characterized by excessive daytime sleepiness even after adequate nocturnal sleep.
      - Symptoms:
        1. Excessive daytime sleepiness
        2. Cataplexy: a reduction or loss of muscle tone
        3. Hallucinations at the time of waking or falling asleep
        4. Sleep paralysis

15.5 Circadian Rhythms and Society

School Start Times

  • Most U.S. middle and high schools start the day too early, with 5 out of 6 starting before 8:30 AM.
      - The American Academy of Pediatrics recommends starting no earlier than 8:30 AM to ensure students get adequate sleep.

Sleep Requirements for Adolescents

  • Teens need at least 8 hours of sleep per night, while younger students require at least 9 hours.
  • 2 out of 3 U.S. high school students report sleeping less than 8 hours on school nights.
      - Source: CDC website on sleep recommendations.

Consequences of Sleep Deprivation

  • Adolescents lacking sufficient sleep are more likely to:
      - Be overweight
      - Engage in unhealthy behaviors like alcohol and drug use
      - Suffer from depressive symptoms
      - Perform poorly academically.

Social Jetlag

  • Defined as the misalignment of an individual's sleep/wake schedule on weekdays compared to weekends, leading to poor sleep quality and chronic partial sleep deprivation.
      - Linked to reduced attention, increased fatigue, and poor performance; associated with obesity, diabetes, and depression.

Medical Intern Hours Regulations

  • As of July 2003, the U.S. Accreditation Council for Graduate Medical Studies set intern/resident limits:
      - Maximum of 80 hours/week
      - 24-hour maximum shifts
      - At least 1 day off per week with 10 hours between shifts

Study on Intern Shift Hours

  • A comparative study reported a 0.25% decrease in absolute mortality and a 3.7% reduction in relative risk of death following these regulations.
  • Errors made by interns on 30-hour shifts included:
      - Overdosing on medications
      - Misdiagnosing conditions
      - Procedural mistakes, such as draining fluid from the wrong lung.

Reasons for Traditional Shift Patterns

  • Tradition and training value to see through treatment courses.
  • Reducing patient handoffs during shifts to improve care quality.