Research into Infradian & Ultradian Rhythms.

Question 1

What is the role of pheromones on the menstrual cycle?

Answer 1

The menstrual cycle is internally controlled by endogenous pacemakers (hormones), which are coordinated by the pituitary gland, to promote ovulation & stimulate the uterus for fertilisation. The menstrual cycle may also be influenced by external zeitgebers (pheromones), which are biochemical substances dispersed into the air from the armpit. The odourless chemicals are detected by other women through an organ in their nose which sends neural signals to the hypothalamus in the brain. The release of these pheromones may therefore coordinate menstrual cycles b/w different women.

Question 2

Outline McClintock’s research findings (1971).

Answer 2

It was found that females who spent extended periods of time together & did not take oral contraceptives, tended to menstruate at the same time every month. The release of pheromones may have facilitated this synchronisation.

Question 3

Evaluation of Research into Infradian Rhythms.

Answer 3

• Supporting evidence for the role of pheromones as an exogenous zeitgeber in the control of the menstrual cycle is provided by Russel et al. (1980): daily samples of sweat were collected from 1 group of women by placing cotton pads under the armpits of donors for 24hrs. Th sweat was then rubbed on the upper lips of other women. Over a number of months, each recipient’s menstrual cycle became synchronised w/ their donor.
• However, there is conflicting evidence for the synchronisation of menstrual cycles due to pheromones: Schank (2006) found w/ Chinese uni students that, there’s no evidence beyond chance that women synchronise their cycles. The perception of synchrony is therefore due to the inevitable variation of menstrual cycles which leads to menstrual cycles coinciding & there’s no actual effect of pheromones on synchronisation.
• Research into menstrual cycle suggests the infradian rhythm is deterministic, which has legal implications. There is irrefutable scientific evidence that the female menstrual cycle is controlled by hormones to prepare the body for pregnancy. A consequence ion the menstrual cycle is pre-menstrual syndrome (PMS).

Question 4

What is the link b/w brain activity & ultradian rhythms?

Answer 4

The regularity of the 90-min sleep stage cycle is partly maintained by endogenous pacemakers. The brain stem acts as a switching mechanism that alternates b/w REM & NREM sleep. When a person is awake, EEGs of the brain activity display high frequency beta wave activity.

• As they fall asleep, the brain stem switches to shallow sleep (NREM stages 1&2), characterised by alpha waves & theta waves which are less frequent & more rhythmic.
• In deep sleep (NREM stages 3&4), high voltage, low frequency delta wave occurs, after which there is gradual return to stage 1.

-The brain stem then switches to REM sleep, which results in beta wave activity & it’s during this time that vivid dreams are reported whilst body experiences sleep paralysis.
Because the brain activity during REM resembles that of an awake brain, REM sleep is aka paradoxical sleep. Brain activity cycles through the stages in this order on average 5 times during a typical night & thus is an ultradian rhythm. Evidence also suggests that the stages of sleep are influenced by exogenous factors (e.g. alcohol, caffeine & exercise).

Question 5

Evaluation of Research into Ultradian Rhythms

Answer 5

• Supporting evidence for ultradian sleep cycles comes from research conducted by Dement & Kleitman (1957): they studied 9 ps who slept for up to 61 nights in a lab whilst their brain activity was recorded using an EEG. They found that activity changed predictably in sleep cycles throughout an entire sleep period. They woke ps during different stages of sleep & found that people awakens during REM sleep reported dreams 80-90% of the time, compared to only 7% for NREM sleep.
• Research into the stages of sleep links to the debate of psychology as a science: the use of a lab setting allows scientists to control conditions to reduce extraneous variables, such as what is consumed before sleep, in order to isolate the role of biological mechanisms. However, to measure the physiology of sleep in a lab, ps are connected to many electrodes, which can affect the quantity & quality of sleep they experience. Therefore, the environment doesn’t reflect the range of factors that can influence sleep in real-life & therefore, lab-based research into sleep lacks ecological validity.
• There is often a lack of population validity in sleep-lab research, as volunteer sampled of young people are often used. Middle-aged people may be busy trying to raise families & succeed at work, so find less time to volunteer for lengthy sleep research. This suggests out knowledge of the stages of sleep is ltd to the use of unrepresentative samples.