Biological rhythms

• Siffre

  case study- spent months in cave isolated from any daylight but found that his sleep/wake cycle still regulated around 25 hours but sometimes ranged to 48hours

  found that daylight acted as an exogenous zietgeber to resynchronise the cycle as the absence altered the circadian rhythm
• Folkard et al (1985)

  12 participants kept in natural light for 3 weeks and exposed to 22hour time cues like alarms and time for food

  11/12 adjusted their sleep/wake cycle

  suggesting that it supports the idea of circadian rhythms as its close to 24 hours and is consistent
• Ralph et al (1990)

  removed the SCN of genetically abnormal hamsters with a 20 hour circadian rhythm and transplanted it into normal hamsters

  the normal hamsters acquired this circadian rhythm showing SCN is important in biorhythms
• Morgan et al (1995)

  removed the SCN from normal hamsters and their circadian rhythm disappeared
• Campbell and Murphy (1998)

  monitored 15 volunteers body temperature and they were woken at different times and a light pad was shon on the backs or their knees

  their circadian rhythms were affected up to 3 hours
• Steele et al (2008)

  investigated 6 participants living in the arctic for 6 weeks where they were in constant daylight- participants kept a sleep diary

  5/6 had a sleep/wake cycle over 24 hours and had no synchronisation of biorhythms
• Stern and McClintock (1998)

  synchronisation of women's menstrual cycles as a result of exposure to pheromones

  68% of women experienced changes to their cycle
• SAD (seasonal affective disorder)

  depression that involves recurrent depressive episodes in a seasonal pattern usually triggered in the winter due to lack of serotonin and increase of melatonin
• The Sleep Cycle


  goes through light sleep (stage 1+2), deep sleep (3+4) and stage 5 and REM
• AO3 of Infradian

  Evolutionary bias of the menstrual cycle- women will have become pregnant at a similar time to raise children collectively to increase chance of survival

  there may be other influences on synchronisation such as stress, diet and exercise
• AO3 of Ultradian Rhythms

  evidence to support distinct sleep stages

  Dement and Kleitman monitored 9 ppts sleep cycles and found a high correlation between REM sleep and dreaming