Circadian Rhythms

• What are biological rhythms ?

  Repeated patterns of change in the body, all regulated by an internal clock (cyclical)
• What are all biological rhythms minted by?

  Endogenous pacemakers and exogenous zeitgebers
• What are endogenous pacemakers?

  • internal cues
  • E.g. cortisol (makes us alert) and melatonin (makes us drowsy)
• What are exogenous zeitgebers?

  • external cues
  • E.g. light outside (signals wake-up) or darkness (signals bedtime)
• What is the master clock called?

  Suprachiasmatic Nucleus (SCN)
• What does the master clock (SCN) do?

  • Controls and synchronises all of the body’s clocks
  • control of the pineal gland means it can regulate hormones like melatonin
• Where is the master clock (SCN) located?

  Hypothalamus
• How can internal / external cues affect the master clock?

  External cues can adjust the internal clock (E.g. SCN uses light cues)
• What did Siffre do?

  • solo cave study
  • Spend period of 2 months and 6 months in a cave (no external cues)
  • Found - his ‘Free running’ rhythm stays around 24/25 hours
  • Regular sleep pattern maintained around 8 hours per night
  • -> endogenous pacemakers regulate the circadian rhythm and can do this without external cues
• What did Folkand et al do?

  • multiple ppts in cave
  • 12 ppts in caved for 3 weeks, would sleep at around 11:45pm and wake 7:45am
  • Researcher (unknown to ppts) secretly adjusts this by speeding up the clock so a day lasted 22hours not 24
  • Found: only 1 ppt adjusted to this cycle. Others kept their free-running (24hr) clock
  • -> endogenous pacemakers aren’t easily overridden by exogenous zeitgebers
• Weakness - lack of generalisability (Siffre)

  • only 1 ppt (himself)- can’t be generalised to anyone else
  • He may have lost objectivity
  • There is no one else to check his findings (not falsifiable)
  • his sleep-wake cycle may have been misinterpreted or confirmation bias (trying to prove his theory) could’ve interfered in the results
  • he though he had only been in there just over a month but he had been 2-> losf track of time
  • = his account may not be reliable, limited sample and potential bias causes it to be unreliable + hard to generalise
• Strength - Real World Application:

  • valuable for shift work (e.g. fire fighters)
  • Working shifts desynchronises circadian rhythms - can lead to psychical/ mental problems
  • = it is useful to advise employers not to repeatedly allocate night shifts to the same people
• Lack of validity

  • both Siffre and Folkands studies didn’t take place in total darkness
  • Artificial light sources were used
  • Lack of control over other variable such as air pressure and temperature (that could’ve impacted rhythm)
  • Exogenous zeitgebers may have still had an effect rather than endogenous pacemakers
  • = studies haven’t tested only endogenous pacemakers, external cues may have impacted results
• Strength - RWA - Chronotherapy

  • can treat real sleep disorders
  • Try to re-set the rhythm for those who struggle to sleep and wake at regular times
  • -> useful to real people in medical / clinical practice