Biological Rhythms

Question 1

Overview of Biological Rhythms

Answer 1

• Definition: Biological rhythms are periodic fluctuations in physiological and psychological processes. They are controlled by internal biological clocks (endogenous pacemakers) and influenced by external cues (exogenous zeitgebers).
• Types of Biological Rhythms:
  1. Circadian rhythms (about 24 hours).
  2. Infradian rhythms (longer than 24 hours).
  3. Ultradian rhythms (shorter than 24 hours).

Question 2

Circadian Rhythms

Answer 2

• Definition: A biological rhythm with a cycle of approximately 24 hours.
• Example: The sleep-wake cycle and the body’s temperature regulation.
• Control Mechanism:
  o Endogenous pacemakers: The suprachiasmatic nucleus (SCN) in the hypothalamus regulates circadian rhythms.
  o Exogenous zeitgebers: Light is the most important external cue, influencing the SCN to regulate wakefulness and sleep.

Question 3

The Sleep-Wake Cycle

Answer 3

• Process:
  o The SCN receives light information from the optic nerve and adjusts the release of melatonin from the pineal gland, promoting sleep when it’s dark.
  o Morning light reduces melatonin production, helping to wake us up.
• Research: Siffre’s cave study showed that in the absence of natural light, the sleep-wake cycle extends beyond 24 hours (around 25 hours), demonstrating the influence of exogenous cues.

Question 4

Core Body Temperature and Circadian Rhythms

Answer 4

• Explanation: Core body temperature follows a circadian rhythm, being lowest around 4:30 AM (36°C) and peaking in the afternoon (around 38°C).
• Impact on Cognition: Cognitive performance is better when body temperature is higher, leading to better alertness and efficiency.

Question 5

Evaluation of Circadian Rhythms

Answer 5

• Strengths:
  1. Research evidence (e.g., Siffre) supports the role of endogenous pacemakers.
  2. Practical applications: Shift work has implications for health (e.g., increased risk of heart disease due to circadian disruption).
  3. Applications in drug timing (chronotherapeutics): Some drugs are more effective at certain times of the day.
• Limitations:
  1. Case studies (e.g., Siffre) lack generalisability.
  2. Individual differences in circadian rhythms (morning people vs. night owls) are not accounted for in some research.

Question 6

Infradian Rhythms

Answer 6

• Definition: A biological rhythm with a cycle longer than 24 hours.
• Examples: The menstrual cycle, Seasonal Affective Disorder (SAD).

Question 7

The Menstrual Cycle

Answer 7

• Process:
  o The menstrual cycle typically lasts about 28 days, regulated by the release of hormones (e.g., estrogen and progesterone).
  o Ovulation occurs around the middle of the cycle (day 14), when estrogen levels peak, followed by a surge in progesterone which helps prepare the uterus for pregnancy.
• Research: Stern and McClintock’s study on pheromones found that menstrual cycles can synchronise among women due to pheromone influence, demonstrating the role of exogenous cues.

Question 8

Seasonal Affective Disorder (SAD)

Answer 8

• Definition: A type of depression that occurs seasonally, typically in winter when daylight hours are shorter.
• Cause: Reduced exposure to natural light disrupts circadian rhythms, leading to increased melatonin production, which may affect serotonin levels and lead to depressive symptoms.
• Treatment: Phototherapy (light therapy) has been shown to be an effective treatment, resetting the body’s circadian rhythms by mimicking sunlight exposure.

Question 9

Evaluation of Infradian Rhythms

Answer 9

• Strengths:
  1. Research on pheromonal influence (e.g., Stern and McClintock) supports exogenous control over biological rhythms.
  2. Applications in treating SAD through phototherapy.
• Limitations:
  1. Methodological issues in studies on menstrual synchrony (e.g., lack of control over other variables).
  2. Evolutionary explanation of menstrual synchrony is debated (e.g., it may have no adaptive function).

Question 10

Ultradian Rhythms

Answer 10

• Definition: A biological rhythm with a cycle shorter than 24 hours.
• Examples: The sleep cycle, appetite regulation.

Question 11

The Sleep Cycle

Answer 11

• Process:
  o The sleep cycle consists of five stages, lasting about 90 minutes per cycle.
  o Stages 1-2: Light sleep, slowing of heart rate and breathing, reduction in muscle tension.
  o Stages 3-4: Deep sleep (slow-wave sleep), delta waves are predominant. This stage is important for physical recovery.
  o Stage 5: REM sleep (rapid eye movement), where dreaming occurs and brain activity resembles waking states.
• Research: Dement and Kleitman found that REM sleep is associated with dreaming, and participants woken during REM reported vivid dreams more often than during other stages.

Question 12

Evaluation of Ultradian Rhythms

Answer 12

• Strengths:
  1. Strong research support for the sleep stages (e.g., Dement and Kleitman).
  2. Understanding sleep stages has practical applications in treating sleep disorders (e.g., insomnia, narcolepsy).
• Limitations:
  1. Individual differences in sleep cycles (e.g., some people have longer cycles) complicate the generalisation of findings.
  2. The functions of REM sleep are still debated (e.g., its role in memory consolidation vs. other functions).

Question 13

Application to Psychological Research

Answer 13

• Circadian Rhythms: Research into shift work and jet lag has practical applications in improving worker health and productivity.
• Infradian Rhythms: Understanding the menstrual cycle and SAD helps in treatment development, including hormonal therapies and light therapy.
• Ultradian Rhythms: Sleep cycle research informs therapies for sleep disorders and improves understanding of memory consolidation during sleep.

Question 14

Key Exam Points

Answer 14

• Definitions: Be clear on the definitions of circadian, infradian, and ultradian rhythms, with examples for each.
• Mechanisms: Understand the role of endogenous pacemakers (e.g., SCN) and exogenous zeitgebers (e.g., light) in regulating biological rhythms.
• Evaluation: Be able to discuss the strengths and limitations of research, particularly in terms of practical applications and methodological issues.