Circadian Rhythms

• What is a circadian rhythm?

  A rhythm that repeats itself on a regular basis over a period of 24 hours
• What psychological functions are influenced by circadian rhythms?

  Functions such as body temperature
• What is photoentrainment?

  It is the synchronization of circadian rhythms with daylight hours through environmental light levels
• What are the two factors that regulate circadian rhythms?

  Endogenous pacemaker and exogenous zeitgebers
• What controls the sleep-wake cycle?

  The SCN (suprachiasmatic nucleus) in the hypothalamus
• When is the strongest sleep drive typically observed?

  Between 2-4 am and 1-3 pm
• How does sleep deprivation affect sleep intensity?

  It makes sleep more intense
• What is the duration of the 'free running' internal circadian clock?

  24-25 hours
• What can disrupt the circadian rhythm?

  Major changes such as jet lag
• How does the homeostatic drive for sleep change throughout the day?

  It increases gradually as energy is used up
• When is core body temperature lowest?

  Around 4:30 am
• When is core body temperature highest?

  Around 6 pm
• How does melatonin production follow a circadian rhythm?

  It peaks during hours of darkness promoting sleepiness
• What is one of the best-known circadian rhythms?

  The sleep-wake cycle
• What are exogenous influences?

  Influences originating from outside the body
• What are endogenous influences?

  Influences originating from inside the body
• What did Siffre (1975) find regarding external cues and circadian rhythms?

  Absence of external cues significantly altered his circadian rhythm
• What did Duffy et al (2001) discover about individual differences in circadian rhythms?

  Morning people prefer to rise and go to bed early, while evening people prefer to wake up and go to bed later
• What is a limitation of research methodology in circadian rhythm studies?

  Participants were not isolated from artificial light
• What did Buhr et al (2010) suggest about temperature and the body clock?

  Temperature controls our body clock rather than light
• How do small fluctuations in body temperature affect our body clocks?

  They set the timing of cells and cause tissues and organs to become active or inactive