Biological Rhythms: Circadian, Ultradian and Infradian Rhythms

Question 1

How is the sleep/wake cycle a circadian rhythm?

Answer 1

A traditional sleep-wake cycle relies on both exogenous zeitgebers and endogenous pacemakers. Light is the most important zeitgeber, and one’s endogenous pacemaker often levels out at around 25 hours.

Question 2

What is Siffre’s cave study?

Answer 2

Michel Suffer spent time in a Southern Alp cave, deprived of exposure to natural light and sound, but with access to adequate food and drink. In each case, his free-running biological rhythm levelled out at 25 hours, though he did sleep and wake on a regular schedule.

Question 3

What is Folkard’s research?

Answer 3

Folkard studied 12 people who agreed to live in a dark cave for 3 weeks, sleeping when the clock said 11:45 and waking when it said 7:45. Over the course of the study, the researchers slowly sped up the clock, so that an apparent 24-hour day was only 22 hours. Only 1 participant adjusted, showing that it is difficult to overcome a strong free-running circadian rhythm.

Question 4

What is the core body temperature circadian rhythm?

Answer 4

It is at its lowest at 4 in the morning (36) and at its highest at 6 in the evening (38). Evidence suggests that body temperature may have an effect on our mental abilities: the warmer we are, the better our cognitive performance. Gupta (1991) found children scored higher on an IQ test at 7PM than one administered at 2pm and 9am.

Question 5

What is the strength - practical application to shift work

Answer 5

Knowledge of circadian rhythms has meant that we know now that night workers experience a reduced concentration around 6 in the morning, making mistakes and accidents more likely. Research also suggested a relationship between shift work and heart disease - 3x more likely to develop it. Thus, research into this may have economic implications in terms of how best to manage worker productivity.

Question 6

What is the strength - practical application to drug treatments?

Answer 6

Circadian rhythms coordinate a number of the body basic processes. This in turn has an effect on pharmacokinetics. Research into this has revealed certain times when drugs are at their most effective - this has led to the development of guidelines to do with the timing of drug-dosing for a range of medications.

Question 7

What is the limitation - use of case studies and small samples?

Answer 7

The people involved may not be representative of the wider population, as most people would not agree to be in a bunker for 3 weeks so it is much less generalisable. Siffre observed that at 60 his internal clock was much slower, so even if the same person is involved, there are factors which prevent conclusions being drawn.

Question 8

What are the two examples of infradian rhythms. Explain

Answer 8

The menstrual cycle - a monthly basis
SAD - an annual basis.

Question 9

What is McClintock’s research?

Answer 9

McClintock demonstrated how menstrual cycles may synchronise as a result of the influence of female pheromones. He gathered 29 women with irregular periods, and samples were gathered from the armpits of 9 of there women. These were then rubbed on the upper lip of the other participants and so on. He found that 68% experienced changes which brought them closer to their ‘odour donor’.

Question 10

What is SAD?

Answer 10

Seasonal Affective Disorder is in the DSM-5 as a type of seasonal depression. It is often triggered by a decrease in the amount of light hours. It is called a circannual rhythm as it is a yearly cycle.

Question 11

Which hormone is implicated in SAD?

Answer 11

Melatonin - the pineal gland secretes melatonin all night until dawn when there is an increase in light. During winter, the lack of light in the morning means that the secretion continues for longer. This has a knock-on effect on serotonin production, ushering in depressive symptoms.

Question 12

What is the main example for Ultradian Rhythms?

Answer 12

Sleep Cycle

Question 13

What are Stages 1 and 2 of the Sleep Cycle?

Answer 13

Light sleep, where the persona can be easily woken. Brainwave patterns become slower and more rhythmic - alpha waves - becoming slower as sleep deepens - theta waves.

Question 14

What are Stages 3 and 4 of the Sleep Cycle?

Answer 14

Delta waves, which are slower with greater amplitude. This is deep sleep or slow wave sleep and it is hard to wake them.

Question 15

What is Stage 5 of the Sleep Cycle?

Answer 15

REM sleep - the body is paralysed yet brain activity speeds up significantly. Rapid Eye Movement is correlated with dreaming.

Question 16

What is the strength - evolutionary basis?

Answer 16

It has been posited that it is evolutionarily beneficent to menstruate together and therefore fall pregnant around the same time. This would mean that newborns could be cared for collectively within a social group, increasing survival chances.

Question 17

What is the counterpoint - evolutionary basis

Answer 17

The validity has been questioned by some. Schank argued that if there were too many females cycling together within a social group, there would be competition for the highest quality males, reducing the fitness of potential offspring. From this view, the avoidance of synchrony seems most evolutionarily successful.

Question 18

What is the limitation - methodological limitations in synchronisation studies

Answer 18

Commentators argue that there are many factors, such as stress or changes in exercise which act as confounding variables. This means that any supposed pattern of synchronisation is no more than would have been expected to occur by chance. In addition, this also involves self-report which can be unreliable.

Question 19

What is the strength - evidence supports the idea of distinct stages in sleep?

Answer 19

A landmark study by Dement and Kleitman monitored the sleep patterns of 9 participants in a lab. Brainwave was recorded on an EEG and caffeine and alcohol was controlled. REM activity was highly correlated with dreaming, and participants woken during dreaming reported very accurate recall of their dreams.