Rhythms

• What are the two main factors that govern biological rhythms?

  Endogenous pacemakers and exogenous zeitgebers
• How does daylight influence our sleep/wake cycle?

  Daylight acts as an important exogenous zeitgeber affecting alertness and drowsiness
• What is the suprachiasmatic nucleus (SCN)?

  It is part of the hypothalamus and acts as an internal clock
• What role does the SCN play in regulating melatonin secretion?

  It regulates melatonin secretion by the pineal gland in response to light/dark cycles
• What is the most influential exogenous zeitgeber?

  Light, specifically sunlight
• What was the purpose of Michael Siffre's cave study?

  To study the effects of deprivation of natural light and sound on biological rhythms
• How long did Siffre believe he had been underground during his first study?

  Two months
• What was the duration of Siffre's second cave study?

  Six months
• What did Siffre's biological rhythm settle to during his studies?

  About 25 hours
• What is a circadian trough and when does it typically occur for night workers?

  A period of reduced concentration around 6 in the morning
• How does shift work relate to health risks?

  Shift workers are three times more likely to develop heart disease
• What is jet lag and how long does it typically take to adjust to a new time zone?

  Jet lag is the adjustment of the body clock after traveling across time zones, taking about a week
• What is chronotherapeutics?

  It is the study of how circadian rhythms affect drug action and timing
• How has research into circadian rhythms influenced drug dosing guidelines?

  It has led to guidelines for timing drug doses for various medications
• What is a limitation of studies on the sleep/wake cycle?

  They often involve small samples that may not represent the wider population
• How did Siffre's age affect his internal clock in his 1999 study?

  His internal clock ticked more slowly than when he was younger
• How do social cues influence infants' sleep/wake cycles?

  Schedules imposed by parents help entrain infants' circadian rhythms
• What is the typical duration of the female menstrual cycle?

  Approximately 28 days, but can range from 24 to 35 days
• What hormone is primarily involved in regulating the menstrual cycle?

  Oestrogen
• What did Stern and McClintock's study demonstrate about menstrual cycles?

  Menstrual cycles may synchronize due to the influence of female pheromones
• What percentage of women experienced changes to their cycle in McClintock's study?

  68%
• What is the evolutionary basis of menstrual synchrony?

  It may have been advantageous for females to menstruate together for collective care of offspring
• What criticism did Schank (2004) make regarding menstrual synchrony?

  Too many females cycling together could lower the fitness of offspring
• What are some confounding variables that may affect menstrual cycles?

  Stress, changes in diet, and exercise
• What is Seasonal Affective Disorder (SAD)?

  A depressive disorder with a seasonal pattern of onset, often triggered in winter
• How is melatonin implicated in SAD?

  Prolonged secretion of melatonin during winter may affect serotonin production
• What is phototherapy and how effective is it for treating SAD?

  It is a light box treatment that can relieve symptoms in up to 60% of sufferers
• What is the typical duration of a sleep cycle?

  90-120 minutes
• How many sleep cycles does a person typically experience in a night?

  Four to five cycles
• What happens to REM sleep as the night progresses?

  REM periods lengthen while deep sleep time decreases
• What are the four stages of sleep?

  Non-REM (Stages 1, 2, 3) and REM sleep
• What is the significance of sleep spindles and K complexes in Stage 2 sleep?

  They protect the brain from awakening during sleep
• What occurs during Stage 3 sleep?

  It is the deepest stage of sleep, most restorative and least likely to be disturbed
• What is the role of human growth hormone during deep sleep?

  It is released to restore the body and muscles
• What happens during REM sleep?

  Breathing becomes rapid, eyes jerk, and vivid dreams occur
• What did Dement and Kleitman's study reveal about REM sleep?

  REM activity is highly correlated with the experience of dreaming
• How did researchers control for confounding variables in Dement and Kleitman's study?

  They controlled for the effects of caffeine and alcohol
• What was the main finding of Dement and Kleitman's research?

  Brain activity varied according to how vivid dreams were