Biological Rhythms

• What are Biological Rhythms?

  They are controlled by internal body clocks and external cues
• What are the three types of Biological Rhythms?

  • Circadian
  • Infradian
  • Ultradian
• What is a Circadian Rhythm?


  A bodily cycle that takes about 24 hours to complete
• What is an example of a circadian rhythm?

  Sleep / wake cycle
• Describe the Sleep / Wake cycle:

  It is governed by daylight and by a biological clock (superchiasmatic nucleus) that gets light information from the eyes
• Supporting Research for Circadian Rhythms:

  • Siffre's case study
  • Spent extended periods of time underground to study the effects on his own biological rhythm
  • Deprived of exposure to natural light
  • After resurfacing his free running biological rhythm had extended to 25 hours
• Supporting research for Circadian Rhythms:

  • Aschoff
  • Participants spent 4 weeks in a WW2 bunker deprived of natural light.
  • All but one of the P’s displayed a circadian rhythm between 24 and 25 hours.
• Supporting Evidence for Circadian Rhythms:

  • Folkard
  • 12 people lived in a cave for 3 weeks.
  • They agreed to go to bed at 11:45pm and get up at 7:45 am.
  • The researchers secretly sped up their clock, so that each “day” lasted only 22 hours.
  • None of the participants could adjust to this.
• Evaluation for Circadian Rhythms - Shift Work:

  • Night workers have a period of reduced concentration about 6am
  • Shift workers are 3x more likely to develop heart disease due to the disruption of their circadian rhythms

  Dealing with these problems could be beneficial for the economy
• Strength of Circadian Rhythms - Medical Treatment:

  • Research has found that there are certain peak times through the day when drugs are likely to be at the most effective.
  • This has led to guidelines on the best time to take certain medications (Chronotherapy)
• Limitation for Circadian Rhythms - Individual Differences:

  • Circadian rhythms have been found ranging from 13-65 hours
  • Duffy (2001) found that people are either more active in the morning (larks) or more active in the evening (owls).
  • Teenager’s CRs are typically 2 hours behind adults’ (sleepy in the morning and wide awake at bedtime)

  This variation makes generalisations difficult.
• Limitation of Circadian Rhythms - Confounding Variables:

  • Although Ps in “free running” studies were deprived of natural light, they still had access to artificial light which was turned on when awake and off when asleep.
  • research has shown that you can adjust the length of an individual’s circadian rhythm using artificial light (it was previously assumed that only natural light could do this).
• What is an Infradian Rhythm?

  A biological rhythm that lasts longer than 24 hours
• What is an example of an Infradian Rhythm?

  Menstrual cycle
• Describe the Menstrual Cycle:

  • Oestrogen levels rise which releases an egg from the ovary during ovulation
  • After ovulation the hormone progesterone helps the lining of the uterus to grow
  • If pregnancy does not occur the egg is absorbed back into the body and the uterus lining leaves the body
  • Takes 24 - 35 days
• Evidence for the role of EZs in the menstrual cycle:

  • Stern and McClintock demonstrated how menstrual cycles may synchronise as a result of the effect of pheromones
  • Studied 29 women with a history of irregular periods
  • Samples of pheromones were gathered from 9 of the women at different stages of the menstrual cycle via cotton pads from armpit
  • Pads were worn for 8 hours
  • Pads were frozen and treated with alcohol
  • Rubbed on upper lip of other Ps
  • Found that 68% of women experienced period changes which brought them closer to their odour donor
• What is seasonal affective disorder?

  • Seasonal affective disorder (SAD) is a type of depression that occurs during specific seasons, typically winter, due to reduced exposure to sunlight.
  • During the night the pineal gland secretes melatonin until dawn when light increases
  • During winter the lack of light in the morning means melatonin is secreted for longer
  • This has a knock on effect on the production of Serotonin
• Strength of Infradian Rhythms - Adaptation

  • Synchronisation may have an adaptive function
  • For distant ancestors it would have been beneficial for women to menstruate together so they have children at the same time so any child that loses their mother still has access to breast milk
  • Improving survivability
• Limitation of Infradian Rhythms - Methodology

  • Methodological shortcomings
  • There are many factors that could effect the menstrual cycle such as stress, changes in diet, exercise etc
  • These may act as confounding variables which means any pattern of synchronisation is by chance
• Strength of Infradian Rhythms - Real World Application:

  • Light therapy reduces the effects of SAD in about 80% of people
  • Light therapy is also preferred over anti depressants as it is safer

  COUNTERPOINT

  -Light therapy can cause headaches and eye strain

  -Relapse rate of 46% over successive winters compared to 27% in a comparison group receiving CBT
• What are Ultradian Rhythms?


  Biological Rhythms that take less than 24 hours to complete
• What is an example of an Ultradian Rhythm?

  The stages of sleep
• Describe the Stages of Sleep:

  • 5 stages that occur in a 90 minute cycle
  • Stages 1 and 2 = Light sleep, in stage one brain waves are high frequency and have short amplitude (Alpha waves). Stage 2 alpha waves continue and sleep spindles occur
  • Stages 3 and 4 = Deep sleep, The brain waves are delta waves with lower frequency and higher amplitude
  • Stage 5 (REM Sleep) = Body is paralyzed yet brain activity is similar to the awake brain. Theta waves are produced, Rapid eye movement, Dreams are most often experienced in REM sleep
• Strength of Ultradian Rhythms - Improved understanding:

  • Understanding of age related changes in sleep has improved
  • SWS reduces with age
  • Could explain issues such as reduced alertness
  • In order to increase SWS relaxation and meditation could be used
• Limitation of Ultradian Rhythms - Individual Differences:

  • There is significant variation between people
  • Tucker et al found large differences between Ps in terms of the duration of each sleep stage, particularly stage 3 and 4
  • These differences are likely to be biologically determined