Circadian Rhythms

1
Circadian Rhythms

• Does the early bird always get the worm?
• Individual and developmental differences in
  circadian rhythms ignored until recently
• Circadian rhythms (from the Latin circa,
  approximately and dies, day) roughly 24-hour
  fluctuations in behavior, from algae to humans
  endogenous, but entrained by exogenous cues
  (zeitgebers)
• The biological clock in humans is in the
  suprachiasmatic nucleus of the hypothalamus

2
Measuring Circadian Rhythms

• Horne Ostberg Morningness-Eveningness
  Questionnaire
• 19 questions, such as Considering only your own
  feeling best rhythm, at what time would you get
  up if you were entirely free to plan your day?
  and If you went to bed at 11PM, at what level of
  tiredness would you be?
• Results 5 categories, from definitely morning
  type to neutral to definitely evening type
• Test is reliable and valid correlates with core
  body temperature, sleep-wake cycles, etc.

3
Developmental and Individual Differences

• Children (lt13 years old) prefer morning
  adolescents and young adults prefer afternoon or
  evening older adults (gt65 years old) prefer
  morning
• Children are variable some are evening types
• 94 of University students evening or neutral
  types none are morning types
• 75 of older adults are morning types, lt2
  evening types
• Synchrony when preferred time of day and task
  demands match

4
Preference scores for children aged 8 to 16 years
(Kim, Dueker, Goldstein, Hasher, 2002)
5
Morningness-Eveningness Distributions(Yoon et
al., 2000)
6
Sentence Recognition by Testing Time(May et
al., 1993)
7
Forgetting of Story Materials (Winocur
Hasher, 2002)
8
Stem Cued Recall of Words(May Hasher, in
preparation)
9
Performance on Stop Signal trials (May
Hasher, 1998)
10
Research Implications

• Childhood are evening type children at risk
  for learning and behaviour problems?
• Adolescence does high school start too early?
• Elderly are cognitive deficits in memory,
  inhibition exaggerated?