Biopsychology: Ultradian and infradian rhythms

Question 1

What is an infradian rhythm?

Answer 1

Rhythms that have a duration of over 24 hours, and maybe weekly, monthly or even annually.

E.G Menstrual cycle
E.G Seasonal affective disorder (SAD)

Question 2

Menstrual cycles: Infradian rhythm

Answer 2

A monthly infradian rhythm is the female menstrual cycle, which is 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.

Question 3

Exogenous zeitgebers may synchronise mentrual cycles:

Answer 3

Stern and McClintock (1988) studied 29 women with irregular periods. Pheromones were taken from some at different stages in their cycles, via a cotton pad under their armpits. These pads were cleaned with alcohol and later rubbed on the upper lips of the other participants. 68% of women experienced changes to their cycle which brought them close to the cycle of their ‘odour donor’. This suggests that the menstrual cycle can be influenced by exogenous factors, such as the cycles of other women.

Question 4

Seasonal affective disorder (SAD): Infradian rhythm.

Answer 4

Seasonal Affective Disorder (SAD) is categorised as a mood disorder which results in feelings of depression, normally brought upon by changes in the seasons.

The majority of individuals with SAD experience symptoms in the winter months (winter blues), making them feel lower in mood and lacking in energy. In rare cases, another form of seasonal depression can occur in the spring and summer months, which can result in irritability and difficulty sleeping. SAD is an infradian rhythm called circannual because the cycle takes longer than 24 hours to complete.

Melatonin located in the pineal gland is predicted to be linked to SAD. During the night melatonin is secreted until dawn and then stops when daylight increases. During the winter, the lack of light in the mornings means melatonin is secreted for longer.

Question 5

What are ultradian rhythms?

Answer 5

Ultradian rhythms take less than 24 hours to complete. An example is the sleep cycle. Psychologists have identified 5 stages of the sleep cycle which span approx. 90 minutes. The cycle continues throughout the course of the night. Each stage is characterised by a different level of brainwave activity which can be monitored using an EEG.

Question 6

What are stages 1 and 2 of the sleep cycle?

Answer 6

Stages 1 and 2 are referred to as the sleep escalators, brain waves become slower as sleep becomes deeper - alpha and theta waves.

Question 7

What are stages 3 and 4 of the sleep cycle?

Answer 7

Stages 3 and 4 are characterised as deep sleep, delta waves are slow and have great amplitude.

Question 8

What is stage 5 of the sleep cycle?

Answer 8

Stage 5 is REM-dreaming, the body is paralysed but brain activity resembles an awake brain.

Question 9

What is the basic rest-activity cycle?

Answer 9

The basic rest–activity cycle (BRAC) is a physiological arousal mechanism in humans proposed by Nathaniel Kleitman, hypothesized to occur during both sleep and wakefulness. Empirically, it is an ultradian rhythm of approximately 90 minutes (80–120 minutes) characterised by different levels of excitement and rest.

Question 10

Evaluating infradian rhythms:

Answer 10

+ Research suggests that the menstrual cycle is, to some extent, governed by exogenous zeitgebers
+ Led to the development of SAD treatment
- Unethical
- Research is based on field experiments

Question 11

A03: Research suggests that the menstrual cycle is, to some extent, governed by exogenous zeitgebers: Infradian rhythms

Answer 11

Research suggests that the menstrual cycle is, to some extent, governed by exogenous zeitgebers (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 12

A03: Led to the development of SAD treatment: Infradian rhythms

Answer 12

Led to the development of SAD treatment. One treatment is phototherapy which is a lightbox that stimulates strong light in the morning and evening thought to rest melatonin levels. This relieves symptoms in 60% of the sufferers (Eastman et al. 1988). However, the same study recorded a placebo effect of 30% using a ‘sham generator’.

Question 13

A03: Unethical: Infradian rhythms

Answer 13

Due to the fact that research into this area tampers with the infradian rhythm of menstruation, research can be criticised as being unethical. Research from McClintock has purposely changed the length of its female participant menstrual cycles. This is a weakness because researchers are not fully aware of the implications of modifying/tampering with such cycles. Such changes could negatively affect female biological processes which is a lack of protection for participants.

Question 14

A03: Research is based on field experiments: Infradian rhythms

Answer 14

In addition, much of the research is based on field experimental methods and therefore the is a lack of control over extraneous variables. For example, researchers such as McClintock are unable to control other external factors that could affect the female menstrual cycle (e.g. stress, exercise/physical activity etc ). This is a weakness because the lack of control over such variables makes it difficult for researchers to confirm a cause-and-effect relationship between the presence of pheromones and the lengthening/shortening of the female menstrual cycle.

Question 15

Evaluating ultradian rhythms:

Answer 15

+ Flexibility of ultradian rhythms
+ Evidence supports the idea of distinct stages in sleep
- Individual differences
- The way in which such research is conducted may tell us little about ultradian rhythms in humans.

Question 16

A03: Flexibility of ultradian rhythms: Ultradian rhythms

Answer 16

An interesting case study indicates the flexibility of ultradian rhythms. Randy Gardener remained awake for 264 hours. While he experienced numerous problems such as blurred vision and disorganised speech, he coped rather well with the massive sleep loss. After this experience, Randy slept for just 15 hours and over several nights he recovered only 25% of his lost sleep. Interestingly, he recovered 70% of Stage 4 sleep, 50% of his REM sleep, and very little of the other stages. These results highlight the large degree of flexibility in terms of the different stages within the sleep cycle and the variable nature of this ultradian rhythm.

Question 17

A03: Evidence supports the idea of distinct stages in sleep: Ultradian rhythms

Answer 17

Evidence supports the idea of distinct stages in sleep. Dement and Kleitman (1957) monitored the sleep patterns of 9 adults using EEG recordings. They found evidence for stages of sleep, specifically REM sleep. Thus, REM (dreaming) sleep is a distinct ultradian rhythm and an important component of the sleep cycle.

Question 18

A03: Individual differences: Ultradian rhythms

Answer 18

The problem with studying sleep cycles is the differences observed in people, which make investigating patterns difficult. Tucker et al. (2007) found significant differences between participants in terms of the duration of each stage, particularly stages 3 and 4 (just before REM sleep). This demonstrates that there may be innate individual differences in ultradian rhythms, which means that it is worth focusing on these differences during investigations into sleep cycles.

Question 19

A03: The way in which such research is conducted may tell us little about ultradian rhythms in humans: Ultradian rhythms

Answer 19

The way in which such research is conducted may tell us little about ultradian rhythms in humans. When investigating sleep patterns, participants must be subjected to a specific level of control and be attached to monitors that measure such rhythms. This may be invasive for the participant, leading them to sleep in a way that does not represent their ordinary sleep cycle. This makes investigating ultradian rhythms, such as the sleep cycle, extremely difficult as their lack of ecological validity could lead to false conclusions being drawn.