Circadian Rhythms

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Circadian Rhythms
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The SleepWaking Cycle

• Biological clock (link to video)
• Siffre (1975) spent 2 months in a cave.
• Wever (1979) several months in a bunker.
• 25 hour cycle suggests a biological clock that
  needs a small amount of external correction imp
  for travel, seasonal variations.

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Neural basis of the biological clock

• Suprachiasmatic nucleus (SCN)
• (sub cluster of hypothalamus).
• Direct link to optic nerve and pineal gland so
  ideal for translating external light dark cycle
  into hormonal fluctuations.
• Shows regularity to the release of melatonin
  (from pineal gland) a key hormone that regulates
  sleep.

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How it works
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• Exogenous factorsLight
• Campbell and Murphy (1998) light on skin was
  used to shift sleep cycle to new light-dark
  cycle.
• Miles et al. (1977) - case study of blind man.
• Luce and Segal (1966) arctic circle dwellers
  ignore light-dark cycle i.e. Can be overridden.

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Endogenous versus exongenous control

• Jet lag
• Shiftwork 10 years shortened life expectancy.
• Seasonal variation

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The Consequences of Disrupting Biological Rhythms

• Jet lag
• Changing time zones Klein et al. (1972)
• Body will slowly adjust using external clues at
  the rate of about 1 hour per day.
• Some people take Melatonin supplements to adjust
  faster
• Melatonin and aircrew US airforce have banned
  its use.

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The Consequences of Disrupting Biological Rhythms

• Shiftwork
• Usually more problematic since the effects span
  more than a few days
• Moore-Ede (1993) shiftworker fatigue costs 77
  billion
• Monk and Folkard (1983)

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Circannual Rhythms

• Rhythms that last for about 1 year or more
• Hibernation/migration undertaken in stable lab
  conditions indicating that it is endogenous

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Circannual Rhythms

• Seasonal Affective Disorder (SAD)
• Severe depression during the winter months
• Seasonal variation in the production of melatonin
  (Barlow Durand, 1995)
• More common in northern latitudes where winter
  days are very short (Terman, 1988)

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Video clips for Lecture day

• Neuron parts and functions
• Want more? This video is from the Kahn academy