Biopsychology - Biological Rhythms

Question 1

What are the key features of circadian rhythms?

Answer 1

• Biological rhythms governed by endogenous pacemakers and exogenous zeitgebers.
• The circadian rhythm lasts for about 24 hours.
• Sleep/wake cycle governed by internal and external mechanisms.
• Siffre demonstrated a free-running circadian rhythm of about 25 hours.
• Aschoff and Wever also found a similar circadian rhythm.
• Endogenous pacemakers may have stronger influence than exogenous zeitgebers.

Question 2

What are biological rhythms governed by?

Answer 2

Biological rhythms are periodic activity, governed by:

1. endogenous pacemakers (internal biological clocks)
2. exogenous zeitgebers (external changes in the environment)

Question 3

What are the 4 different biological rhythms?

Answer 3

1. Ultradian rhythms: last less than 24 hours.
2. Infradian rhythms: last longer than 24 hours.
3. Circadian rhythms: last around 24 hours.
4. Circannual rhythms: last around 12 months.

Question 4

What is the sleep/wake cycle governed by?

Answer 4

The sleep/wake cycle is governed by internal and external mechanisms.

Exogenous zeitgebers - The fact that we feel drowsy when it’s night and alert during the day shows the effect of daylight.

Endogenous pacemakers - There is a basic rhythm governed by the suprachiasmatic nucleus, which lies just above the optic chiasm and receives information about light directly from this structure. The exogenous zeitgeber (light) can reset the suprachiasmatic nucleus.

Question 5

What did Siffre demonstrate?

Answer 5

French caver Siffre spent long periods in dark caves to examine the effects of free-running biological rhythms - two months (in 1962) in the caves of the Southern Alps and six months (in the 1970s) in a Texan cave (when he was 60).

In each case study, Siffre’s free-running circadian rhythm settled down to just above the usual 24 hours (about 25 hours).

Importantly, he did have a regular sleep/wake cycle.

Question 6

What did Aschoff and Wever find?

Answer 6

A group of participants spent four weeks in a World War 2 bunker deprived of natural light (Aschoff and Wever 1976).

All but one (whose sleep/wake cycle extended to 29 hours) displayed a circadian rhythm between 24 and 25 hours.

Question 7

What do Siffre’s study and Aschoff and Wever’s study show?

Answer 7

Siffre’s experience and the bunker study suggest that the ‘natural’ sleep/wake cycle may be slightly longer than 24 hours but is entrained by exogenous zeitgebers associated with our 24-hour day (e.g. number of daylight hours, typical mealtimes, etc.).

Question 8

What evidence suggests that endogenous pacemakers may have stronger influence than exogenous zeitgebers?

Answer 8

Folkard et al. (1985) studied a group of 12 people who live in a dark cave for three weeks, going to bed when the clock said 11:45pm and waking when it said 7:45am.

The researchers gradually sped up the clock (unbeknown to the participants) so an apparent 24-hour day eventually lasted only 22 hours.

Only one participant comfortably adjusted to the new regime. This suggests the existence of a strong free-running circadian rhythm that cannot easily be overridden by changes in the external environment.

Question 9

What are the strengths of circadian rhythm research?

Answer 9

• practical application to shift work

- practical application to drug treatments

Question 10

What are the weaknesses of circadian rhythm research?

Answer 10

• use of case studies and small samples in studies
• poor control in research studies
• individual differences may have an influence on results

Question 11

What practical application to shift work is there of circadian rhythms?

Answer 11

Boivin et al. (1996) found shift workers experience a lapse of concentration around 6am (a circadian trough) so mistakes and accidents are more likely.

Research also suggests a link between shift work and poor health, with shift workers three times more likely to develop heart disease (Knutsson 2003).

Thus, research into the sleep/wake cycle may have economic implications in terms of how best to manage worker productivity.

Question 12

What practical application to drug treatments is there of circadian rhythms?

Answer 12

Circadian rhythms coordinate the body’s basic processes (e.g. heart rate, hormone levels) with implications for pharmacokinetics (action of drugs on the body and how well they are absorbed and distributed).

Research shows there are times during the day or night when drugs are more effective. Guidelines have been developed for the timing of dosing for a range of drugs including treatments for cancer and epilepsy (Baraldo 2008).

Thus research into circadian rhythms may have real-life medical benefits.

Question 13

Why is the use of case studies and small samples in circadian rhythm studies a limitation?

Answer 13

Studies of the sleep/wake cycle often use small groups of participants (e.g. Aschoff and Wever), or even single individuals (e.g. Siffre).

Participants may not be representative of the wider population and this limits making meaningful generalisations. Siffre observed that his internal clock ticked much more slowly at 60 than when he was younger.

This suggests that, even when the same person is involved, there are factors that may prevent general conclusions being drawn.

Question 14

How is there poor control in circadian rhythm research studies?

Answer 14

Participants deprived of natural light still had access to artificial light (e.g. Siffre had a lamp turned on from when he woke up until he went to bed). Artificial light was assumed to have no effect on free-running rhythms.

But Czeisler et al. (1999) adjusted participants’ circadian rhythms from 22 to 28 hours using dim lighting. Using artificial light may be like taking a drug that resets participants’ biological clocks.

This suggests that researchers may have ignored an important confounding variable in circadian rhythm research.

Question 15

How may individual differences have an influence on results found from circadian rhythm research studies?

Answer 15

An issue complicating the generalisation of findings from studies of the sleep/wake cycle is that individual cycles can vary from 13 to 65 hours (Czeisler et al. 1999).

Also, Duffy et al. (2001) found some people display a natural preference for sleeping and rising early (‘larks’) but others prefer the opposite (‘owls’). There are also ahe differences in sleep/wake patterns.

This means that findings from sleep/wake cycle studies may not fully represent individual differences within the population.

Question 16

What are key features of infradian rhythms?

Answer 16

• The female menstrual cycle is an infradian rhythm.
• Exogenous zeitgebers may synchronise menstrual cycles.
• Seasonal affective disorder is another infradian rhythm.
• Seasonal affective disorder may be caused by the hormone melatonin.

Question 17

How is the female menstrual cycle an example of an infradian rhythm?

Answer 17

The human female menstrual cycle is about 28 days (less than one cycle in 24 hours).

Rising levels of oestrogen cause the ovary to develop and release an egg (ovulation). Then progesterone helps the womb lining to thicken, readying the body for pregnancy. If pregnancy does not occur, the egg is absorbed into the body and the womb lining comes away and leaves the body (menstrual flow).

Question 18

How can exogenous zeitgebers synchronise menstrual cycles?

Answer 18

Stern and McClintock (1998) studied 29 women with irregular periods. Pheromones were taken from some at different stages of their cycles, via a cotton pad under the 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 closer to the cycle of their ‘odour donor’.

Question 19

How is seasonal affective disorder an example of an infradian rhythm?

Answer 19

Seasonal affective disorder is a depressive disorder (low mood, lack of activity) with a season pattern.

Often called the ‘winter blues’ because the symptoms are triggered during the winder months when the number of daylight hours becomes shorter.

SAD is an infradian rhythm called a circannual (yearly) cycle.

Question 20

What hormone may seasonal affective disorder be caused by?

Answer 20

During the night, the pineal gland secretes melatonin until dawn when there is an increase in light.

During winter, the lack of light in the morning means secretion goes on for longer.

This has a knock-on effect on the production of serotonin in the brain (low serotonin is linked to depressive symptoms).

Question 21

What are key features of ultradian rhythms?

Answer 21

• Stages of sleep are an ultradian rhythm.

- Five stages of sleep have been identified.

Question 22

How are stages of sleep an ultradian rhythm?

Answer 22

Sleep pattern occurs in 90-minute periods (more than one cycle in 24 hours).

Divided into five stages, each characterised by a different level of brainwave activity (monitored using EEG).

Question 23

How are stages of sleep an ultradian rhythm?

Answer 23

Sleep pattern occurs in 90-minute periods (more than one cycle in 24 hours).

Divided into five stages, each characterised by a different level of brainwave activity (monitored using EEG).

Question 24

What are the five stages of sleep?

Answer 24

Stages 1 and 2: light sleep. Person may be easily woken. Brainwaves become slower and more rhythmic (alpha waves), slowing further as sleep becomes deeper (beta waves).

Stages 3 and 4: deep sleep. Slow wave sleep characterised by delta waves which are slower still and have a greater amplitude.

Stage 5: REM (rapid eye movement) sleep. Fast, jerky activity of eyes. Sensory blockade and movement inhibition (sleep paralysis), but brain activity speeds up.

Question 25

What are the strengths of research into infradian and ultradian rhythms?

Answer 25

• research on the menstrual cycle shows its evolutionary value
• evidence supports qualitatively different stages in sleep
• research into season affective disorder has practical application

Question 26

What are the weaknesses of research into infradian and ultradian rhythms?

Answer 26

• the methodology used in synchronisation studies

- the use of animal studies

Question 27

How does research on the menstrual cycle show its evolutionary value?

Answer 27

It may have been advantageous for our ancestor females to menstruate together and become pregnant around the same time, so offspring could be cared for collectively, increasing their chances of survival.

However, Schank (2004) questions the validity of this perspective - too many females cycling together within a social group would produce competition for highest quality males (lowering the fitness of potential offspring).

From this point of view, the avoidance of synchrony would appear to be the most adaptive evolutionary strategy and therefore the one that would be naturally selected.

Question 28

How does evidence support qualitatively different stages in sleep?

Answer 28

A landmark study by Dement and Kleitman (1957) monitored the sleep patterns of nine participants in a sleep lab and found evidence for stages of sleep, specifically REM sleep.

REM activity during sleep correlated with dreaming; brain activity varied according to how vivid dreams were; participants woken during dreaming reported accurate recall of their dreams.

The study suggests that REM (dreaming) sleep is a distinct ultradian rhythm and an important component of the ultradian sleep cycle.

Question 29

What are the practical applications of research into seasonal affective disorder?

Answer 29

An effective treatment for SAD is phototherapy, a lightbox that stimulates strong light in the morning and evening (thought to reset melatonin levels).

This relieves symptoms in up to 60% of sufferers (Eastman et al. 1988). But the same study recorded a placebo effect of 30% using a ‘sham negative-ion generator’.

This casts doubt on the real value of phototherapy, which may only be affective because of expectations.

Question 30

Why is the methodology used in synchronisation studies a weakness?

Answer 30

Commentators argue that there are many factors that may change a woman’s menstrual cycle and act as confounding variables in research (e.g. stress, changes in diet).

So any pattern of synchronisation (e.g. in Stern and McClintock’s study) is what we would expect to occur by chance. Also, research involves small samples of women and relies on them self-reporting onset of their own cycle (may be inaccurate).

This suggests that important aspects of synchronisation studies may lack validity.

Question 31

Why is the use of animal studies in infradian and ultradian rhythm research a weakness?

Answer 31

The role of pheromones in animal sexual behaviour is well-documented and is the basis for most of our knowledge.

For example, sea urchins release pheromones into the surrounding water so other urchins eject their sex cells simultaneously.

In contrast, evidence for the effects of pheromones on human behaviour remains speculative and inconclusive.