biological rhythms

Biological Rhythms

Overview of Biological Rhythms

  • Biological rhythms can be categorized into two main types: infradian and ultradian rhythms.
Infradian Rhythms
  • Definition: Infradian rhythms are biological rhythms with a frequency of less than one cycle in 24 hours.
  • Examples:
    • Menstrual Cycle
    • Governed by monthly hormonal changes regulating ovulation.
    • Defined as the time between the first day of a woman's period (womb lining shedding) to the day before the next period, typically around 28 days (range: 24 to 35 days).
    • Hormones involved:
      • Oestrogen: Causes the ovary to develop an egg and trigger ovulation.
      • Progesterone: Thickens the womb lining in preparation for pregnancy. If pregnancy does not occur, the egg is reabsorbed, and the lining is shed.
    • Seasonal Affective Disorder (SAD)
    • A depressive disorder with symptoms triggered during winter months due to reduced daylight (often referred to as the winter blues).
    • Considered a circannual rhythm (yearly cycle) but can also fit as a circadian rhythm due to its disruption by long periods of darkness affecting the sleep/wake cycle.
    • Melatonin's Role in SAD:
      • Secreted by the pineal gland during the night; prolonged secretion occurs in winter due to lack of morning light.
      • This prolonged secretion potentially affects serotonin production leading to depressive symptoms.
Ultradian Rhythms
  • Definition: Ultradian rhythms are biological rhythms that occur more than once within a 24-hour cycle.
  • Example: Stages of Sleep (Sleep Cycle)
    • Five distinct stages of sleep spanning about 90 minutes, repeating throughout the night.
    • Each stage has a unique brainwave activity profile measured using EEG (electroencephalograms).
    • Stages of Sleep:
    1. Stage 1: Light sleep with alpha waves. Easily woken.
    2. Stage 2: Features alpha waves and sleep spindles. Light sleep.
    3. Stage 3: Slow-wave sleep (SWS) with delta waves. Difficult to wake the person.
    4. Stage 4: Deep sleep with delta waves and high amplitude. Very hard to awaken.
    5. Stage 5 (REM sleep): Body paralyzed; brain activity resembles that of wakefulness with theta waves. Dreams occur during this stage.

Measurement of Brainwaves

  • EEGs: Used for measuring brainwaves in laboratories, facilitating detailed studies of sleep patterns and neural activity.
  • Recent Advances: Shift from paper printouts to digital imaging for enhanced analysis of brain activity during sleep.

Applications and Considerations

Menstrual Synchrony
  • Evidence suggests menstrual cycles may synchronize among women due to pheromonal influence (study by Kathleen Stern and Martha McClintock, 1998).
    • Methodology: Pheromone samples collected from women in different cycle stages and applied to others resulted in 68% experiencing synchronization.
Strengths and Limits of EEGs
  • Strengths: Enable detailed observation of brain changes during sleep.
  • Limitations: Participants often arrive after sleep deprivation, affecting natural sleep patterns.
Evaluation of Infradian Rhythms
  1. Evolutionary Basis: Synchronization in menstrual cycles may have provided evolutionary advantages for communal child-rearing.
  2. Methodological Limitations: Other factors (diet, stress, lifestyle changes) could impact menstrual cycles, confounding results. Past studies have failed to replicate findings.
Seasonal Affective Disorder (SAD) Treatment
  • Light Therapy: Much of the efficacy seen via light therapy, which mimics sunlight and reset circadian rhythms, showing effectiveness in about 80% of individuals.
  • Challenges: Potential side effects include headaches and eye strain; relapses are recorded at rates higher than alternative treatments like CBT.

Understanding Sleep and Ultradian Rhythms

  • Age-related Changes: Older adults exhibit reduced slow wave sleep; implications include reduced alertness due to diminished growth hormone production during these stages.
  • Individual Differences: Research shows significant variations in sleep stages duration among different individuals, complicating the identification of 'normal' sleep patterns.
The Basic Rest-Activity Cycle (BRAC)
  • Research indicates a 90-minute cycle of alertness followed by fatigue, akin to sleep cycles, also applicable to alertness during waking hours. Suggested connection to optimizing study sessions for maximum focus.
    • Ericsson's Study: Top violinists practice in sessions of no longer than 90 minutes to maximize performance.
Methodological Approach in Studies on SAD
  • Design: Patients assigned to receiving either treatment or no treatment for effect comparison (statistical analysis on mood after therapy).

Review Questions

  1. Name an ultradian rhythm.
  2. What does psychological research indicate about infradian rhythms?
  3. Evaluate research findings concerning infradian and/or ultradian rhythms.