L12 - Biological Rhythms - Infradian & Ultraradian Rhythms

Question 1

Infradian rhythms

Answer 1

Infradian rhythms span a period of longer than 24 hours; they may last weeks, months or even a year. Examples of the infradian rhythms include: the menstrual cycle and seasonal affective disorder.

Question 2

Ultradian rhythms

Answer 2

• frequency of more than one cycle in 24 hours and can be found in the pattern of human sleep
• the stages of sleep is an example of an ultradian rhythm.
• sleep cycle alternates between REM (rapid eye movement) and NREM (non-rapid eye movement) sleep and consists of five stages.
• starts at light sleep, progressing to deep sleep and then REM sleep, where brain waves speed up and dreaming occurs.
• This repeats itself about every 90 minutes throughout the night.

Question 3

Complete sleep cycle

Answer 3

Has four stages of NREM sleep before entering REM (Stage 5) and then repeating.
Research using EEG has highlighted distinct brain waves patterns during the different stages of sleep.
1. Stages 1 and 2 are ‘light sleep’ stages. During these stages brainwave patterns become slower and more rhythmic, starting with alpha waves progress to theta waves.
2. Stages 3 and 4 are ‘deep sleep’ or slow wave sleep stages, where it is difficult to wake someone up. This stage is associated with slower delta waves.
3. Finally, Stage 5 is REM (or dream) sleep. Here is the body is paralysed (to stop the person acting out their dream) and brain activity resembles that of an awake person. In this stage the EEG machine will be reading theta waves.
- On average, the entire cycle repeats every 90 minutes and a person can experience up to five full cycles in a night.

Question 4

What has the 90 minute cycle been referred to?

Answer 4

Kleitman (1969) referred to the 90 minute cycle found during sleep as the Basic Rest Activity Cycle (BRAC). He suggested that this 90 minute cycle continues when we are awake.
- During the day, rather than moving through the sleep stages, we move progressively from a state of alertness into a state of physiological fatigue.
- Research suggests that the human mind can focus for about 90 minutes, and towards the end of those 90 minutes the body begins to run out of resources, resulting in loss of concentration, fatigue and hunger.
- key study to support the stages of sleep was by Dement and Kleitmen in 1957.

Question 5

Dement and Kleitmen (1957)

Answer 5

Procedure: seven adult males and two adult females took part in the study - asked to report to the laboratory at bedtime where they were connected to an EEG. (for up to 61 nights).
- The EEG took measurements throughout their time asleep, all night. Pps were asked not to drink caffeinated drinks for the day before their sleep was investigated.
- During the night, Pps were woken at different stages of sleep by the sound of bell. They would also be awoken between 5 and 15 minutes of their REM sleep. (they were woken up to six times in a night). - Once awake, they would then speak into a recording machine by their bed about if they had been dreaming and if they could remember the details of their dream.
Findings:
1) All pps had periods of REM sleep every night.
2) They found high incidences of dream recall when pps were awakened during REM sleep. When awakened in other stages, very few pps reported of dreaming.
3) When looking for a relationship between brain activity and dreams, they found that the brain activity was different in very vivid dreams to the less clear dreams.

Question 6

Dement and Kleitmen (1957) conclusion

Answer 6

Conclusion: From the above research, it can be concluded that the stages of sleep follow a typical pattern throughout the night, and dreams occur in REM sleep. This study therefore supports the idea that stages of sleep are an example of an ultradian rhythm and occur more than once in the night (in 24 hours)

Question 7

Evaluation of ultradian rhythms

Answer 7

strengths
- Dement and Kleitmen (1957)
- BRAC support
weaknesses
- individual differences

Question 8

BRAC support

Answer 8

• Ericsson et al. (2006) found support for BRAC.
• studied a group of elite violinists and found that among this group practise sessions were limited to 90 minutes at a time.
• Violinists frequently napped to recover from practise, with the best violinists napping more.
• The same pattern was found among musicians, athletics, chess players and writers.
• This study shows that ultradian rhythms can help to explain that for maximum performance 90 minutes practice is the best. This study further supports that ultradian rhythms occur.

Question 9

Individual differences

Answer 9

• There are individual differences in sleep patterns so we can’t generalise the stages of sleep to all.
• Tucker et al. (2007) suggests that there are individual differences in sleep patterns, which are biologically determined and may even be genetic in origin.
• Participants were studied over 11 consecutive days and nights in a laboratory environment.
• The researchers assessed sleep duration, time to fall asleep and the amount of time in each sleep stage.
• They found differences in all of these characteristics. This study shows that we need to be cautious about generalising how ultradian rhythms work with regards to stages of sleep since some people who may not go through these stages do not necessarily have abnormal sleep!

Question 10

Types of Infradian rhythms

Answer 10

• menstrual cycle
• SAD (seasonal affective disorder)

Question 11

What does SAD stand for?

Answer 11

Seasonal affective disorder

Question 12

Menstrual cycle

Answer 12

• regulated by hormones that either promote ovulation or stimulate the uterus for fertilisation.
• Ovulation occurs roughly halfway through the cycle when oestrogen levels are at their highest, and usually lasts for 16-32 hours.
• After the ovulatory phase, progesterone levels increase in preparation for the possible implantation of an embryo in the uterus.
• It is also important to note that although the usual menstrual cycle is around 28 days, there is considerable variation, with some women experiencing a short cycle of 23 days and others experiencing longer cycles of up to 36 days.
• Although the menstrual cycle is an endogenous system, evidence suggests that it may be influenced by exogenous factors, such as the cycles of other women.

Question 13

Menstrual cycle evaluation

Answer 13

strengths
- external factors on Infradian rhythms
- exogenous zeitegebers research
- evolutionary psychologists
- regulators of behaviour
weaknesses
- methodological limitations
- environmentally determinist

Question 14

External factors on Infradian rhythms

Answer 14

Research suggests that the menstrual cycle is, to some extent, governed by exogenous zeitegebers (external factors). Reinberg (1967) examined a woman who spent three months in a cave with only a small lamp to provide light. Reinberg noted that her menstrual cycle shortened from the usual 28 days to 25.7 days. This result suggests that the lack of light (an exogenous zeitgeber) in the cave affected her menstrual cycle, and therefore this demonstrates the effect of external factors on infradian rhythms.

Question 15

exogenous zeitgebers research

Answer 15

There is further evidence to suggest that exogenous zeitgebers can affect infradian rhythms. Russell et al. (1980) found that female menstrual cycles became synchronised with other females through odour exposure. In one study, sweat samples from one group of women were rubbed onto the upper lip of another group. Despite the fact that the two groups were separate, their menstrual cycles synchronised. This suggests that the synchronisation of menstrual cycles can be affected by pheromones, which have an effect on people nearby rather than on the person producing them. These findings indicate that external factors must be taken into consideration when investigating infradian rhythms like the menstrual cycle.

Question 16

Evolutionary psychologists

Answer 16

Another strength of studying the menstrual cycle as an infradian rhythm can be supported by evolutionary psychologists who claim that the synchronised menstrual cycle provides an evolutionary advantage for groups of women, as the synchronisation of pregnancies means that childcare can be shared among multiple mothers who have children at the same time. This means that the research is useful and has practical advanatages.

Question 17

Regulators of behaviour

Answer 17

There is research to suggest that infradian rhythms such as the menstrual cycle are also important regulators of behaviour. Penton-Volk et al. (1999) found that woman expressed a preference for feminised faces at the least fertile stage of their menstrual cycle, and for a more masculine face at their most fertile point. These findings indicate that women’s sexual behaviour is motivated by their infradian rhythms, highlighting the importance of studying infradian rhythms in relation to human behaviour.

Question 18

methodological limitations

Answer 18

There are methodological limitations in menstrual synchronisation studies. For example, there
are many factors that may effect change to the menstrual cycle, including stress, changes in
diet, exercise, etc. These may act as confounding variables, which means that any supposed
patterns of synchronisation is no more than would have been expected to occur by chance. This
may explain why other studies have failed to replicate the findings. This suggests that
menstrual synchrony studies are flawed which then questions whether this is good scientific
evidence to support the menstrual cycle as an infradian rhythm.

Question 19

environmentally determinist

Answer 19

Furthermore, most research seems to focus on the influence of exogenous zeitgebers such as
Pheromones and seems to ignore the importance of endogenous pacemakers that control the
menstrual cycle – it is therefore environmentally determinist.

Question 20

Evaluation - SAD

Answer 20

• research support
• practical applications
• placebo effect

Question 21

Research support

Answer 21

Evidence supports the role of melatonin in SAD. Terman (1988) found that the rate of SAD is more common in Northern countries where the winter nights are longer. For example, Terman found that SAD affects roughly 10% of people living in New Hampshire (a northern part of the US) and only 2% of residents in southern Florida. These results suggest that SAD is in part affected by light (exogenous zeitgeber) that results in increased levels of melatonin.

Question 22

Practical applications

Answer 22

Another strength of studying the infradian rhythm in terms of SAD, is the practical applications of it. One of the most effective treatments for SAD is phototherapy- a lightbox that simulates very strong light in the morning and evening. This is thought to reset melatonin levels, which in turn regulates serotonin levels, and improves symptoms in up to 60% of sufferers (Eastman et al, 1998). This supports the idea that SAD is specifically caused by a reduction in light leading to biochemical imbalances.

Question 23

Placebo affect

Answer 23

However the same study (Eastman et al, 1998) found that 30% of participants showed improvement when treated with a placebo (a pretend ‘negative ion generator’). This suggests that the effectiveness phototherapy might in part be due to the placebo effect.