Infradian rhythms and Ultradian rhythms

Question 1

Infradian rhythms (IR) - Menstrual Cycle

Answer 1

Governed by monthly changes in hormone levels which regulate ovulation.
During each cycle, rising levels of the hormone oestrogen cause the ovary to develop an egg and release it - ovulation.
After ovulation, the hormone progesterone helps the womb lining to grow thicker, readying the body for pregnancy.
If pregnancy doesn’t occur, the egg is absorbed into the body, the womb lining comes away and leaves the body - menstrual flow.

Question 2

(IR) Although the menstrual cycle is an…

Answer 2

Endogenous system, evidence suggests that it may be influenced by exogenous factors, such as the cycles of other women.

Question 3

(IR) A study by Kathleen Stern and Martha McClintock (1998) demonstrates…

Answer 3

How menstrual cycles may synchronise as a result of the influence of female pheromones.

Question 4

(IR) McClintock’s pps

Answer 4

29 women with a history of irregular periods.

Question 5

(IR) How were samples of pheromones were gathered?

Answer 5

From 9 of the women at different stages of their menstrual cycles, via a cotton pad placed in their armpit.
The pads were worn for at least 8 hours to ensure that pheromones were picked up. The pads were treated with alcohol and frozen, to be rubbed on the upper lip of the other pps.
On day 1, pads from the start of the menstrual cycle were applied to all 20 women, on day 2 they were all given a pad from the 2nd day of the cycle, and so on.

Question 6

(IR) McClintock’s results

Answer 6

Found that 68% of women experienced changes to their cycle which brought them closer to the cycle of their ‘odour donor’.

Question 7

(IR) Seasonal affective disorder - SAD

Answer 7

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

Question 8

(IR) SAD’s symptoms

Answer 8

Persistent low mood with a general lack of activity and interest in life.
Referred to winter blues as symptoms are triggered during winter months when the number of daylight hours becomes shorter.
A particular type of infradian rhythm - circannual rhythm; subject to a yearly cycle.
Experience of SAD may be due to the disruption of the sleep/wake cycle and can be attributed to prolonged periods of daily darkness during winter.

Question 9

(IR) Psychologists have hypothesised that the hormone melatonin is…

Answer 9

Implicated in the cause of SAD.
During the night, the pineal gland secretes melatonin until sawn when there’s 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 on the production of serotonin in the brain - a chemical that has been linked to the onset of depressive symptoms.

Question 10

Ultradian rhythms (UR) - stages of sleep.

Answer 10

5 stages with approximately a span of 90 minutes - cycle continuing throughout the course of the night.

Question 11

(UR) Each of the stages is…

Answer 11

characterised by a different level of brainwave activity which can be monitored using an EEG.

Question 12

(UR) Stages 1 and 2

Answer 12

‘Sleep escalator’ - light sleep where the person may be easily woken.
Beginning of sleep, brainwave patterns start to become slower and more rhythmic (alpha waves), becoming even slower as sleep becomes deeper (theta waves).

Question 13

(UR) Stages 3 and 4

Answer 13

Delta waves - slower still and have a greater amplitude than earlier wave patterns; deep sleep or slow-wave sleep and difficult to rouse someone at this point.

Question 14

(UR) Stage 5 - REM sleep

Answer 14

The body’s paralysed yet brain activity speeds up significantly in a manner that resembles the awake brain.
REM = rapid eye movement to denote the fast, jerky activity of the eyes under the eyelids at the point.
Research has suggested that REM activity during sleep is highly correlated with the experience of dreaming.

Question 15

Weakness - methodological limitations of synchronisation studies

Answer 15

Criticisms have been made of early synchronisation studies and the methods employed.
Commentators argue that there are many factors that may affect change in a women’s menstrual cycle, including stress, changes in diet, exercise, etc., that might act as confounding variables. This means that any supposed pattern of synchronisation, as seen in s studies by McClintock and others, is no more than would have been expected to occur by chance.
In addition, research typically involves small samples of women and relies on pps self-reporting the onset of their own cycle.
Other studies failed to find any evidence of menstrual synchrony in all-female samples.

Question 16

Strength - Evidence supports the idea of distinct stages in sleep

Answer 16

A landmark study by William Dement and Nathaniel Kleitman (1957) monitored the sleep patterns of nine adult pps in a sleep lab. Brainwave activity was recorded on an EEG and the researchers controlled for the effects of caffeine and alcohol. REM activity during sleep was highly correlated with the experience of dreaming were, and pps woken during dreaming reported very accurate recall of their dreams.
Replications of this investigation have noted similar findings, though the small size of the original sample has been criticised by some. Nevertheless, this study suggests that REM sleep is an important component of the ultradian sleep cycle.

Question 17

Strength/ Weakness - animal studies

Answer 17

Much of the knowledge of the effects of pheromones on behaviour is derived from animal studies. The role of pheromones in animal sexual selection is well-documented. For instance, the fact that sea urchins release pheromones into the surrounding water so other urchins in the colony will eject their sex cells simultaneously. In contrast, evidence for the effects on human behaviour remains speculative and inconclusive.

Question 18

Strength/ Weakness - Practical application of SAD

Answer 18

One of the most effective treatments for SAD is phototherapy. This is a lightbox that stimulates very strong light in the morning and evening. It is thought to reset melatonin levels in people with SAD. This relieves symptoms in up to 60% of sufferers (Eastman et al, 1998). However, the same study recorded a placebo effect of 30% using a ‘sham negative-ion generator’. This casts doubt on the chemical influence of phototherapy.

Question 19

Strength - evolutionary basis of the menstrual cycle

Answer 19

Menstrual synchrony, of the kind observed in the McClintock study, is thought by many to have an evolutionary value. For our ancestors it may have been advantageous for females to menstruate together and therefore fall pregnant around the same time. This would mean that new-borns could be cared for collectively within a social group increasing the chances of the offspring’s survival.
The validity of the evolutionary perspective has been questioned by some. Jeffrey Schank (2004) has argued that if there were too many females cycling together within a social group, this would produce competition for the highest quality males (and thereby lowering the fitness of any potential offspring). From this point of view, the avoidance of synchrony would appear to be most adaptive evolutionary strategy and therefore naturally selected.