Biological rhythms: circadian, infradian and ultradian and the difference between these rhythms.

Question 1

Define biological rhythms

Answer 1

Distinct patterns of changes in the body activity that conform to cyclical time periods. Biological rhythms are influenced by internal body clocks (endogenous pacemakers) as well as external changes to the environment (exogenous zeitgebers)

Question 2

What is a simple definition of biological rhythm?

Answer 2

A biological rhythm is a cyclical variation over some period of time.

Question 3

What are biological rhythms governed by?

Answer 3

1. The body’s internal biological ‘clocks’ - endogenous pacemakers
2. external changes in the environment - exogenous zeitgebers

Question 4

What are the 3 different types of biological rhythm?

Answer 4

1. Circadian
2. Infradian
3. Ultradian

Question 5

Define circadian rhythms

Answer 5

Biological rhythms, subject to a 24 hour cycle, which regulate a number of body processes such as the sleep/wake cycle and changes in core body temperature

Question 6

What are circadian rhythms influenced by?

Answer 6

Endogenous pacemakers – this is the body’s internal biological clock.

Exogenous Zeitgebers – literally means external time givers. Clues from our environment that influence the biological rhythms such as light, darkness.

Question 7

How long does the circadian rhythm last?

Answer 7

A 24 hour period

Question 8

Give an example of a circadian rhythm

Answer 8

the sleep/wake cycle

Question 9

How do exogenous zeitgebers / external cues influence the sleep/wake cycle?

Answer 9

The sleep wake cycles is governed by external cues such as light and darkness. These exogenous zeitgebers are important in guiding the sleep wake cycle.

Question 10

How do endogenous pacemakers/ internal cues influence the sleep/wake cycle?

Answer 10

there is also an internal (endogenous) ‘clock’. This is free running – it works without any external cues – setting a cycle around 24 – 25 hours.

Question 11

Who did research on the circadian rhythm / sleep wake cycle?

Answer 11

Siffre

Question 12

What did Siffre do?

Answer 12

Spent several periods underground to study the effects of his own biological rhythms. Underground, in a cave, he had no external cues to guide his rhythms – no daylight, no clocks, no radio. He simply woke, ate, and slept when he felt like it. The only thing influencing his behaviour was his internal ‘clock’ or ‘free-running rhythm.

Question 13

What did Siffre find?

Answer 13

After his first underground stay of 61 days , he resurfaced on 17th September believing the date was 20th August. On the second occasion he spent 6 months in a cave, his circadian rhythm settled to just over 24 hours but this would sometimes change to 48 hours. On his final underground study (he was 60 years old) he found that his internal biological clock ticked more slowly compared to when he was a young man.

Question 14

Who provides support for Siffre?

Answer 14

Aschoff + Weaver

Question 15

What did Aschoff + Weaver do?

Answer 15

Convinced a group of participants to spend 4 weeks in a WW2 bunker deprived of natural light.

Question 16

What did Aschoff + Weaver find?

Answer 16

1 participant showed a very extended circadian sleep/wake cycle of 29 hours. The rest all showed an extended circadian sleep/wake cycle of between 24-25 hours.

Question 17

What does Siffre’s + Aschoff + Weaver’s studies show?

Answer 17

The ‘natural’ sleep/wake cycle may be slightly longer than 24 hrs but that it is entrained by exogenous zeitgebers associated with our 24-hour day (such as the number of daylight hours, typical mealtimes etc.)

Question 18

What did Folkard study?

Answer 18

Studied a group of 12 people who agreed to live in a dark cave for 3 weeks, retiring to bed when the clock said 11:45pm and rising when it said 7:45am.

Question 19

What did Folkard do?

Answer 19

Over the course of the study, the researchers gradually speeded up the clock (unbeknown to the ppts), so an apparent 24 hour day eventually lasted only 22 hours!

Question 20

What did Folkard find?

Answer 20

Only one of the participants was able to comfortably adjust to the new regime. This would suggest the existence of a strong free-running circadian rhythm that cannot easily be overridden by exogenous zeitgebers.

Question 21

Give an example of another circadian rhythm

Answer 21

Another circadian rhythm is shown by your body temperature.

Question 22

What is core body temperature?

Answer 22

Core body temperature is the physical state at which the internal organs and bodily systems function at an optimal level.

Question 23

When is your core body temperature the lowest and highest?

Answer 23

Your body temperature is lowest around 04.30, and highest around 18:00.
Higher temperature seems to be linked with better mental performance.

Question 24

Explain the link between circadian rhythms + core body temperature

Answer 24

The circadian rhythm has been linked to changes in core body temperature which in turn has been related to cognitive abilities.
Research demonstrating core body temperature as a circadian rhythm linked to performance was conducted by Folkard et al. (1977).

Question 25

Explain Folkard’s research on circadian rhythm + core body temperature

Answer 25

They looked at the learning ability of 12- and 13-year-old children who had stories read to them at either 9.00 am or 3.00 pm. After one week, the afternoon group (higher core body temperature) showed both superior recall and comprehension, retaining about 8% more meaningful material. Therefore, this research shows the circadian rhythm of core body temperature effects cognitive ability.

Question 26

Define infradian rhythm

Answer 26

A type of biological rhythm with a frequency of less than one cycle in 24 hours, such as menstruation and seasonal affective disorder.

Question 27

How long is an infradian rhythm?

Answer 27

Longer than a day e.g. a week or a month

Question 28

What is the clearest example of an infradian rhythm?

Answer 28

The menstrual cycle. On average this cycle takes 28 days but there are individual variations between 20-60 days

Question 29

What is the menstrual cycle governed by?

Answer 29

It is governed by hormones i.e. an endogenous mechanism. During the cycle, rising levels of oestrogen cause the ovary to develop an egg and release it (ovulation). After ovulation, progesterone helps the womb lining to grow thicker, readying the womb for pregnancy. If pregnancy doesn’t occur, the egg is absorbed back into the body, the womb lining comes away and leaves the body (the menstrual flow).

Question 30

What is the function of the menstrual cycle?

Answer 30

The function of the menstrual cycle is to regulate ovulation. The pituitary gland releases hormones which stimulate a follicle in one ovary to ripen the egg and also triggers the release of the female hormone oestrogen. Once the egg has ripened the ruptured follicle starts to secrete progesterone which causes the lining of the womb to prepare for pregnancy - if after 2 weeks there is no pregnancy, progesterone is reduced and this causes the lining of the womb to be shed.

Question 31

Who did research on infradian rhythm / menstrual cycle?

Answer 31

McClintock + Stern

Question 32

What did McClintock + Stern investigate?

Answer 32

Whether the menstrual cycle (endogenous system) is influenced by phermone secretions from other women (exogenous factor)

Question 33

What was McClintock + Stern’s sample?

Answer 33

29 female university students, not taking birth control pills.

Question 34

Describe McClintock + Stern’s study

Answer 34

A control group of women wore an alcohol soaked pad in their armpits. The phermones were then rubbed on the top lip of another group of women (the experimental group) and their menstrual cycles monitored.

Question 35

What did McClintock + Stern find?

Answer 35

69% of the ppts in the experimental group showed changes in their own menstrual cycle timings which brought them closer to the cycle of the ppts in the control group who they received the phermones from. This supports the role of Exogenous zeitgebers in human infradian rhythms.

Question 36

What did McClintock + Stern conclude?

Answer 36

the experimental groups’ menstrual cycles were affected by the secretions from the control group. This explains why when a group of women live in close proximity their menstrual cycles tend to synchronise.

Question 37

What did Russel do?

Answer 37

Russell et al conducted a study where their sample consisted of female university students, not taking birth control pills. Daily samples of sweat were collected from one group of women and rubbed on the upper lip of women in a second group.

Question 38

What did Russel find?

Answer 38

The groups were kept separate yet their menstrual cycles became synchronised. This suggest that the synchronisation of the menstrual cycle can be affected by pheromones.

Question 39

What is seasonal affective disorder (SAD)?

Answer 39

A depressive disorder which has a seasonal pattern of onset, and is described and diagnosed as a mental disorder in DSM-5.

Question 40

What are the main symptoms of SAD?

Answer 40

Persistent low moods alongside a general lack of activity and interest in life. Symptoms are triggered during the winter months when the number of daylight hours become shorter.

Question 41

How is SAD an example of an infradian rhythm?

Answer 41

SAD is a particular type of infradian rhythm called a circannual rhythm as it is subject to a yearly cycle. However it can also be classed as a circadian rhythm as the experience of SAD may be due to the disruption of the sleep/wake cycle and this can be attributed to prolonged periods of daily darkness during winter.

Question 42

What have psychologists found about SAD?

Answer 42

The hormone melatonin is a cause. During the night the pineal gland secretes melatonin until dawn when there is an increase in light. During winter, the lack of light in the morning means this secretion process continues for longer. This is thought to have a knock-on effect in the production of serotonin in the brain - a chemical that has been linked to the onset of depressive symptoms.

Question 43

Define ultradian rhythms

Answer 43

A type of biological rhythm with a frequency of more than one cycle in 24 hours, such as the stages of sleep (the sleep cycle).

Question 44

What is the length of ultradian rhythms?

Answer 44

Ultradian rhythms are shorter than a day (24hours) in length. The stages of sleep are the clearest example of the Ultradian rhythm in humans.

Question 45

Why are the stages of sleep the clearest example of ultradian rhythms in humans?

Answer 45

Sleep is a repetition of 5 stages through the night - therefore it is a rhythm that happens within a 24 hour period, making it ultradian. Sleep progresses to deeper and deeper sleep from stages 1-5. These stages are in cycles of 90 minutes. Then this is reversed, but instead of going back to stage 1, REM sleep is experienced instead.

Question 46

What happens in stage 1 of sleep?

Answer 46

– Relaxed, feeling drowsy, hypnogogic state where we might have hallucinatory images. Characterised by alpha waves on EEG

Question 47

What happens in stage 2 of sleep?

Answer 47

Characterised by slower and larger waves – theta waves with short bursts of sleep spindles (high frequency waves). It is still easy to wake in this stage

Question 48

What happens in stage 3 of sleep?

Answer 48

Brain waves slow down. Deeper sleep characterised by long slow delta waves and some sleep spindles

Question 49

What happens in stage 4 of sleep?

Answer 49

Mainly delta waves known as slow wave sleep (SWS) Hard to wake in this stage but personally significant noises like your baby crying will wake you. Body temperature drops and growth hormone is produced. Sleep walking/talking and night terrors can occur.

Question 50

What happens in stage 5 sleep?

Answer 50

Stage 5 = REM sleep where we experience dreams. (Stage 5) REM sleep is characterised by rapid eye movements, your muscles are paralysed to stop you acting out your dreams and is shown as desynchronised EEG activity resembling the awake state
EEG indicates the brain is very active showing beta activity but it is the hardest stage to wake from so it is known as paradoxical sleep

Question 51

Who provides research for the sleep cycle?

Answer 51

Dement + Kleitman

Question 52

What did Dement + Kleitman do?

Answer 52

Dement and Kleitman (1957) monitored electrical activity in the brain during sleep using EEG recordings and so could wake participants during the different stages of sleep. They woke ppts during the different stages of sleep.

Question 53

What did Dement + Kleitman find?

Answer 53

People awakened during REM sleep reported dreaming 90 per cent of the time. Dreams were recalled in detail, including elaborative visual images. Only 7 percent of awakenings from NREM led to dream recall. This supports the stages of sleep, in particular the role of REM sleep for dreaming.