Infradian and Ulfradian Rhythms

Question 1

Infradian rhythms (IR)

Answer 1

• type of biological rhythm, with a frequency of less than one cycle in 24 hours
• an example of infradian rhythms is the menstrual cycle

Question 2

IR - menstrual cycle

Answer 2

• menstrual cycle is controlled by monthly hormone level changes which regulate ovulation
• one cycle is time between the first day of the period and the day before the next period, which is typically 28 days
• ovary develops an egg as a result of rising levels of oestrogen, and the egg is released
• after ovulation progesterone is introduced, which helps the womb to grow thicker, as well as readying the body for pregnancy
• if the woman is not pregnant then the egg is absorbed into the body and the womb lining comes away
• this lining leaves the body as menstrual flow

Question 3

IR - Stern and McClintock (1998) - aim

Answer 3

• conducted experiment to demonstrate how menstrual cycles may synchronise due to influence of pheromones
• this supports the idea that the endogenous system of the menstrual cycle may be influenced by exogenous zeitgebers

Question 4

IR - Stern and McClintock (1998) - procedure

Answer 4

• 29 women were involved in the study, all of which had a history of irregular periods
• pheromone samples were taken from 9 of them at different stages of the menstrual cycles using cotton pads on the armpits
• the pads were work for 8 hours to absorb the pheromones
• they were then treated with alcohol and frozen, and then rubbed on the upper lip of the other 20 participants
• the 20 participants being given the pads were given pads from the day of the menstrual period in correspondence with the day of pad exposure they were on

Question 5

IR - Stern and McClintock (1998) - findings

Answer 5

• 68% of the women were found to have experienced changes to their menstrual cycle
• their cycle and the cycle of the ‘odour donor’ were brought more in synch

Question 6

IR - seasonal affective disorder

Answer 6

• depressive disorder with seasonal pattern of onset
• it is described and diagnosed as a mental disorder by the DSM-V
• the main symptoms are persistent low mode and general lack of interest in life or any other activities
• this disorder only occurs in winter months, when number of daylight hours decrease
• SAD is a specific type of infradian rhythm known as a circannual rhythm, which happens on a yearly cycle
• melatonin has been hypothesised to be the cause of SAD
• the pineal gland secretes melatonin at night, until dawn when light increases
• the lack of light in the winter mornings means that this melatonin release continues for longer, and is thought to have a knock-on effect in relation to the production of serotonin

Question 7

Ultradian rhythms

Answer 7

• type of biological rhythms which have a frequency of more than one cycle in 24 hours e.g. the sleep cycle

Question 8

UR - sleep cycle

Answer 8

• one of the most extensively researched ultradian rhythms
• 5 stages have been identified by psychologists which span 90 minutes then repeated throughout the night
• an EEG can monitor the different brainwave activity levels which characterise each stage

Question 9

UR - sleep cycle stages

Answer 9

Stages 1 and 2

• light sleep
• the person can easily be woken up
• brainwave patterns become slower and more rhythmic at the beginning of sleep
• theses are alpha waves
• as sleep becomes deeper they become slower, known as theta waves

Stages 3 and 4

• delta waves are present, which are even slower as the sleep becomes deeper
• it is quite difficult to wake someone up in this sleep stage

Stage 5

• REM sleep, when the body is paralysed yet brain activity increases further
• REM stands for rapid eye movement, which refers to the fast and jerky actions of the eyes under the eyelids
• REM activity and the experience of dreaming are highly correlated

Question 10

EVAL - evolutionary basis of the menstrual cycle

Answer 10

• the synchronisation of the menstrual cycle is though to have an evolutionary value
• it may have been beneficial for females in the past to menstruate and thus fall pregnant at around the same time
• babies could be cared for all together, which would increase their chances of survival
• Schank (2004) and others have questioned the validity of this evolutionary perspective however
• too many females totters within a social group would produce competition for the highest quality of males, lowering the fitness of any potential offspring
• this would mean that avoidance of synchrony would be the most adaptive evolutionary strategy

Question 11

(-) EVAL - methodological limitations in synchronisation studies

Answer 11

• early synchronisation studies and the methods used have been criticised
• it is argued that there are a number of factors affected the woman’s menstrual cycle e.g. exercise, diet, stress, etc.
• these may all be confounding variables
• this would mean that any pattern spotted in Stern and McClintock’s (1998) study would just have happened by chance
• as well as this, typically only small samples are used, and self-report techniques are relied upon to record data
• there are also a number of studies, e.g. Trevathan et al. (1993) that fail to find evidence of menstrual synchrony

Question 12

(+) EVAL - evidence supporting the idea of distinct stages in sleep

Answer 12

• Dement and Kleitman (1957)
• monitored sleep patterns of 9 adult participants
• an EEG was used to record brain activity, with researchers controlling for effects of caffeine and alcohol
• a high correlation was found between REM activity and dreaming
• brain activity varied according to how vivid the dreams were
• if participants were woken up during a dream they could very accurately recall their dreams
• this study suggests that REM sleep is an important component of sleep cycle