Circadian Rhythms

• Define circadian rhythm

  -A type of biological rhythm, subject to a 24-hour cycle, which regulates a number of body processes such as the sleep-wake cycle and core body temperature.
• Define biological rhythm

  -Distinct patterns of changes in body activity that conform to cyclical time periods.

  -They are influenced by endogenous pacemakers and exogenous zeitgebers
• What did Michael Siffre's do

  -He performed an experiment where he spent two months in a cave in the Southern Alps.

  -He had access to food and drink but no exposure to natural light or sound.

  -He resurfaced in mid-September 1962, believing it to be mid-August. He did a similar experiment a decade later, this time spending 6 months in a Texan cave.​

  -His biological rhythm settled down to one that was just beyond the usual 24 hours
• Outline Aschoff & Weber's study

  -They got a group of participants to spend four weeks in a WWII bunker, deprived of natural light. All but one of the participants (whose sleep/wake cycle extended to 29 hours) displayed a circadian rhythm of 24-25 hours.
• What do both these studies show

  -Both the bunker and cave studies suggest that the natural sleep/wake cycle may be slightly longer than 24 hours, but that it is entrained by exogenous zeitgebers.
• Outline Simon Folkards study

  -studied a group of 12 people who agreed to live in a dark cave for three weeks. ​

  -They were told to go to sleep when the clock said 11:45 and get up at 7:45. ​

  -Unbeknown to the participants, the clock was gradually sped up, so that an apparent 24 hours day became a 22-hour day. ​

  -None of the participants could comfortably adjust to the new regime.
• What does this suggest?

  -This suggests that the existence of a strong-free running circadian rhythm that cannot be overly overwritten by environmental cues.
• Define a free running circadian rhythm

  -refers to the natural, intrinsic cycle of a biological rhythm when it is not synchronized with external cues like the light-dark cycle
• Core Body temp varies by around how many degrees during the day?

  -2 degrees
• It is at its lowest

  -It is at its lowest (approx. 360C) around 4am and at its highest (380C) at around 6pm.
• Evidence suggests that

  -body temperature may have an effect on our mental abilities; the warmer we are the better we cognitively perform.
• What did Folkard found that children...

  -who had stories read to them at 3pm had superior recall and comprehension after one week than those that had them read to them at 9am.
• What did Gupta find?

  -improved performance on IQ tests when participants were assessed at 7pm as opposed to 2pm and 9am.