BP - Biological rhythms

Question 1

Biological Rhythms

Answer 1

• Cyclical changes in body activity

Question 2

Circadian Rhythms

Answer 2

A type of biological rhythm in which a pattern of behaviours occurs or recurs approximately every 24 hours and which is set and reset by environmental light levels.
Examples of CR are sleep-wake cycles and temperature control.

Question 3

Endogenous pacemakers

Answer 3

• Internal body clocks that regulate many biological rhythms

Question 4

Exogenous zeitgebers - short

Answer 4

• External cues that may effect (retrain or regulate) our biological rhythms

Question 5

Infradian rhythms

Answer 5

• A type of biological rhythm that has a duration of over 24 hours

Question 6

Ultradian rhythms

Answer 6

• A type of biological rhythm with a duration of less that 24 hours, or has multiple cycles within a 24 hour period

Question 7

How do circadian rhythms work?

Answer 7

Comes from the Latin ‘circa’ = about, and ‘diem’ = day (about a day)

• Our CR are driven by our body clocks found in all body cells which are synchronised by the master circadian ‘pacemaker’ - the suprachiasmatic nucleus (SCN) found in the hypothalamus
• This pace maker must be constantly reset so that our bodies are in synchrony with the outside world; light acts as the primary input to this system, setting the body clock to the correct time in a process of photoentrainment
• Light-sensitive receptor cells in the eyes act as brightness detectors sending messages about environmental light levels directly to the SCN via the optic nerve
• The SCN then uses this information to coordinate the activity of the entire circadian system (even with eyes closed, light still penetrates eyelids)

Question 8

How does the sleep-wake cycle work as a CR?

Answer 8

• The CR dictates when we sleep and when we should be awake
• In the morning, our eye cells detect light and so messages are sent via the optic nerve to the SCN which sends messages to raise our blood pressure and body temperature and delay the release of hormones like melatonin from the pineal gland
• As a result, in the morning, we have our sharpest rise in blood pressure and the reduction in melatonin secretion makes us feel awake, helped by high levels of cortisol in the morning
• We are therefore at our cognitive best in the late morning, where we have high levels of alertness, perception, attention, memory and other sensory / mental processes due to cortisol being high and melatonin being low
• In the evening, with the sun (natural light) disappearing, the SCN picks up signals of changing light from our eyes and so it sends messages to ensure our body temperature cools and sleep inducing hormones like melatonin are released from the pineal gland - therefore, in the evening, our body signals it is time to sleep

Question 9

When does the circadian rhythm of the sleep-wake cycle dip and rise?

Answer 9

• This happens throughout the day, with our strongest sleep drive happening around 2am-4am and 1pm-3pm (post-lunch dip)
• The sleepiness experienced in these circadian dips is less intense with sufficient sleep, and more intense when we are sleep deprived
• There is also a slight dip in body temperature between 2pm and 4pm which may also contribute to the post-lunch dip
• Sleep and wakefulness are not solely decided by the circadian rhythms alone, but are also under homeostatic control, as when we have been awake for long periods of time, homeostasis tells us the need for sleep is increasing because of the amount of energy ‘used up’ during wakefulness
• This homeostatic need for sleep increases throughout the day, reaching its maximum in the late evening when most people fall asleep

Question 10

How does the circadian system deal with changes?

Answer 10

• It keeps us awake as long as their is daylight, prompting us to sleep as it becomes dark, and the homeostatic system also increases sleepiness throughout the day, regardless of light in the environment
• The circadian system is intolerant of any major alterations in sleep and wake schedules (e.g. travel or shift work) because this causes the biological clock an d the internal systems that depend on it to become completely out of balance
• Chronic disruption to the CR of sleep/wake can lead to obesity, fatigue, diabetes and insomnia

Question 11

Evidence for Circadian rhythms - Siffre

Answer 11

Siffre spent several extended periods underground to study the effects on his own biological rhythms

• This deprived him of exposure to natural light and sound, but with access to adequate food and drink, Siffre resurfaced after two months in the caves of the Southern Alps
• A decade after, he performed a similar study for 6 months in a Texas cave
• In each case, his free running biological rhythms settle down to one that was just beyond the usual 24 hours (around 25) though he did fall asleep on a regular schedule

Question 12

Evidence for Circadian rhythms - Aschoff and Wever (1976)

Answer 12

• They convinced a group of participants to spend 4 weeks in a WWII bunker deprived of natural light, with all but one of the participants displaying a circadian rhythm of between 24-25 hours
• Both of these studies suggested the natural sleep-wake cycle may be slightly longer than 24 hours but that it is entrained by exogenous zeitgebers associated with the 24 hour day, like typical meal times and daylight hours

Question 13

Evidence of Circadian rhythms - Folkard et al. (1985)

Answer 13

• Studied a group of 12 people who agreed to live in a cave for 3 weeks, retiring to bed when the clock said 11:45 pm and rising when it read 7:45 am
• Over the course of the study, the researchers gradually sped the clock up without the participants knowledge, and so an apparent 24 hour day only lasted 22
• It was revealed that not one of the participants were able to comfortably adjust to the new regime, suggesting the existence of a strong free running circadian rhythm that cannot easily be overridden by changes to the external environment

Question 14

Evaluation of Circadian rhythms - Strengths

Answer 14

Practical application to shift work -

• Shift work has been linked to desynchronisation of circadian rhythms and can lead to adverse cognitive and physiological effects
• Research has shown that night shift workers suffer concentration lapse at 6am, increasing the likelihood of accidents, and shift workers are also 3 times more likely to suffer from heart disease as a result of the stress of adjusting to sleep/wake cycles
• This is a strength as research on CR has highlighted the practical and economic implications of shift work in terms of maintaining worker productivity and preventing accidents in the workplace
• A counter argument of this evidence is poor control in studies

Application: Pharmacokinetics

• By understanding CR and their health impacts, it can help determine the best times to administer drug treatments
• For example, the risk of heart attack is greatest early in the morning so drugs can be taken at night, but not released until they will be most effective at dusk
• This is a strength as it means research has a practical purpose and application, such as timing drug dosing of a whole range of medications including anti-cancer, cardiovascular and anti-epileptic drugs
• This means there are peak times for administration of dosage of a variety of drugs to increase their efficacy

Support from the ‘cave study’

• Research to support the existence of CR, such as the work of Siffre, who despite spending seven months in Southern Alps caves found his CR remained at around 24-25 hours
• This suggests the body’s internal clock is set at 24-25 hours in the absence of external cues, and is intolerant of any major alterations to sleep and wake cycles through processes like shift work and jet lag - this is a strength as it shows the concept has research support and therefore may be valid
• Further research by A&W (WW2 bunker study) concluded also that exogenous zeitgebers may have an impact on mediating the cycle after their participants had a CR of 25 hours for sleep/wake cycles
• However, Folkard’s study provides other research, whose participants had a massive impact on their well being after their Circadian sleep/wake cycle was shortened to 22 hours - suggests how much the CR is set in stone

Question 15

Evaluation of CR - Weaknesses

Answer 15

Issues with case study evidence -

• The Siffre study was on one individual, and A&W and F both only used a handful of people
• Consequently, it is impossible to generalise their results to whole populations as there may be some differences in research samples that make participants sleep/wake in atypical ways
• For example, Siffre noted that when he went in the cave at 60 years old, he found his body responded differently with his body clock following more of a 48hr cycle - Czeisler has found evidence that cycles could vary as much as 13-65 hours
• This is a weakness, suggesting results lack external validity, as factors like age and gender may have significant impacts on our CR

Poor control in studies -

• In cave studies, exposure to artificial light such as torches / phones was not controlled
• It was assumed that it was only natural light that has an influence on our biological rhythms - however, research by Czeisler found that dim artificial lighting could adjust the CR between 22-28 hours
• This is a weakness as it means the results to the original studies may lack ecological validity and the sleep/wake cycle may vary considerably more
• Additionally, the impact of artificial lighting on our CR also has practical implications when it comes to the use of electronic devices such as iPad and smartphones during different times of the day

Question 16

The general circadian rhythm cycle

Answer 16

06: 45 - sharpest rise in blood pressure
07: 30 - Melatonin secretion stops
08: 30 - Bowel movement likely
09: 00 - Highest testosterone secretion
10: 00 - High alertness
14: 30 - Best coordination / strongest etc
15: 30 - Fastest reaction time
17: 00 - Greatest cardiovascular efficiency and muscle strength
18: 30 - Highest blood pressure
19: 00 - Highest body temperature
21: 00 - Melatonin secretion starts
22: 30 - Bowel movements suppressed
02: 00 - Deepest sleep
04: 30 - Lowest body temperature

Question 17

Ultradian rhythms - sleep cycle

Answer 17

The Sleep cycle;

• Stage 1 - light sleep, muscle activity slows down, occasional muscle twitching, forms about 4-5% of the cycle
• Stage 2 - light sleep, breathing pattern and HR slow, slight decrease in body temperature, forms about 45-55% of cycle
• Stage 3 - deeper sleep, brain begins to generate slow delta waves, 4-6% of cycle
• Stage 4 - deep sleep, rhythmic breathing, limited muscle activity, brain produces delta waves, 12-15%
• Stage 5 - rapid eye movement, brainwaves speed up and dreaming occurs, muscles relax and heart rate increases, breathing is rapid and shallow 20-25%

One cycle of all stages last around 90 minutes, and around 4 of these occur in one night.

Question 18

Ultradian rhythms - The basic rest-activity cycle (BRAC)

Answer 18

• Kleitman (1969) suggested that a similar 90 minute cycle continues during waking hours and he called this the basic rest-activity cycle
• This is characterised by periods of alertness followed by periods of physiological fatigue which occurs across a 90 minute cycle which recurs throughout the day
• Research suggests that the human mind can focus for about 90 minutes and towards the end of this 90 minute period, the body begins to run out of resources, resulting in a loss of concentration, fatigue and hunger
• Ericsson et al (1993) found that the best performers in a study of violinists were those who tended to practise for 3 sessions during the course of the day, with each session lasting 90 minutes and having a break in between too recharge

Question 19

Infradian rhythm - the menstrual cycle

Answer 19

• 28 days in length - period happens around day 21, lasts 2-7 days, and ovulation occurs around day 10-16
• Hormones involved - FSH, oestrogen, LH and progesterone
• FSH and LH - released by pituitary
• O and P - ovaries
• LH - releases matured egg from ovaries, and stimulates the release of oestrogen and progesterone
• FSH - Triggers maturing of eggs in ovary, and stimulates oestrogen production to start building womb lining
• O - inhibits FSH production, stimulates LH release and causes ovaries to mature egg and build lining
• P - helps to maintain womb lining by thickening womb lining, readying the womb for the implantation of a fertilised egg
• Ovulation occurs when O levels are highest, and if pregnancy does not occur, the egg is observed by the body and the womb lining comes away and leaves the body - the menstrual flow

Question 20

Evidence for the infradian rhythm of the menstrual cycle

Answer 20

Stern and McClintock - 1998:

• Studied 29 women with irregular periods, gathering samples of pheromones from 9 women at different stages of their menstrual cycle via a cotton pad placed in the armpit for 8 hours, before treating the pads with alcohol and freezing them to place them on the upper lip of the other 20 women
• On day one of their cycles, they received the pheromones from the first day of the sample, and the same happened for the rest of their cycles
• Found that 68% of women experienced changes to their menstrual cycle which brought them closer to the cycle of their ‘odour donor’

Factors that could affect menstrual cycle other than pheromones -
- Age, diet, exercise, stress and weight fluctuation, dehydration

Criticisms -
- Small sample size, lack of causality, not fully controlled

Question 21

Infradian rhythm - Seasonal Affective Disorder

Answer 21

• A form of depression which has a seasonal pattern of onset - ‘winter blues’
• Main symptoms - low mood persistently, changes in appetite, weight loss, general lack of activity and interest in life and feelings of despair
• It is triggered during the winter months when the number of daylight hours becomes shorter
• Psychologists have hypothesised the hormone melatonin is implicated as a main cause of SAD; 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 the secretion process continues for longer which is thought to have a knock on effect on the production - a chemical linked to the onset of depressive symptoms

Question 22

Evaluation of infradian and ultradian rhythms - supporting evidence

Answer 22

1. Stern and McClintock’s 1998 study - supports the endogenous infradian rhythm of the menstrual cycle, but it also suggests that it may be influenced by exogenous, such as the cycles of other women
2. Menstrual synchrony as found in S&M’s study is thought to have evolutionary value as it would be advantageous for females to menstruate together and therefore fall pregnant at the same time, which would result in new-borns being cared for collectively within a social group, which would increase chances of the survival of the offspring
   - This supports the importance of the endogenous infradian rhythm of the MC
   - However, the validity of this evolutionary perspective has been questioned - if there are too many females in a social group synced up, this would produce competition for the highest quality males (thereby lowering fitness of potential offspring)

Question 23

Evaluation of infradian and ultradian rhythms - supporting evidence 2

Answer 23

3. Derment and Kleitman (1957) - monitored sleep patterns of nine adult participants in a sleep lab, recording brainwave activity 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, brain activity varied according to the vividity of dreams, and participants woken during their REM cycle reported very accurate recall of dreams
   - This suggests REM sleep is an important component of the ultradian sleep cycle and that there are distinct sleep stages, with replications of the investigation have noted similar findings, although the size of the original sample has been criticised
4. Ericsson et al (2006) study - found through analysis that the very best violinists napping more than their teachers, and they found the same pattern among the other musicians, athletes, chess players and writers
   - This is consistent with the claim that fatigue is a characteristic of the end of the BRAC cycle which occurs in a roughly 90 minute cycle, and therefore supports the ultradian rhythm

Question 24

Evaluation of infradian and ultradian rhythms - supporting evidence 3

Answer 24

5. One of the most effective treatments for SAD is phototherapy, where sufferers spend time next to a lightbox that stimulates very strong light in the morning and evening, which is thought to reset melatonin levels in those with SAD - this relieves symptoms in 60% of sufferers
   - This supports the importance of knowing about infradian rhythms and therefore the external validity of this theory, however the same study recorded a placebo effect of 30% using a ‘sham negative ion generator’ which they were told was another form of treatment
   - This casts doubt on the chemical influence of phototherapy and implies thinking you are receiving treatment is more important than the actual treatment; consequently this calls into question the thinking behind the causes of the infradian rhythm

Question 25

Evaluating of infradian and ultradian rhythms - weaknesses

Answer 25

There are many criticisms of early synchronisation studies and the methods employed in studies like S&M’s - there may be other factors that change a woman’s menstrual cycle that act as confounding variables, such as changes in diet and exercise.

• Furthermore, research typically uses small sample sizes and relies on self-reporting - additionally, other studies have failed to find any evidence of menstrual synchronicity in all-female samples
• This suggests that any supposed pattern of synchronisation of infradian rhythms between women is no more than would have been expected to occur by chance - we cannot internally validate this idea from research as we cannot determine cause and effect; additionally, results may not be externally valid either, and so even if cause and effect was determined, we cannot generalise it to all women

Question 26

Endogenous pacemakers evidence

Answer 26

DeCoursey et al. (2000)
- They destroyed the SCN connections in the brains of 30 chipmunks who were then returned to their natural habitat and observed for 80 days. The sleep-wake cycle of the chipmunks disappeared and by the end of the study a significant proportion of them had been killed by predators (presumably because they were awake and vulnerable to attack when they should have been asleep).

Ralph et al. (1990)
- They bred ‘mutant’ hamsters with a 20-hour sleep-wake cycle. When SCN cells from the foetal tissue of ‘mutant’ hamsters were transplanted into the brains of normal hamsters, the cycles of the second group defaulted to 20 hours.

Question 27

Exogenous Zeitgebers evidence

Answer 27

Campbell and Murphy (1998)

• They demonstrated that light may be detected by skin receptor sites on the body even when the same information is not received by the eyes
• 15 participants were woken at various stages of the sleep cycle and a light pad was shone on their knees
• The researchers managed to produce a deviation in the participants usual sleep-wake cycle of up to 3 hours in some cases

Burgess et al (2003)

• They found that exposure to bright light prior to an east-west flight decreased the time needed to readjust to local time on arrival
• Volunteers participated in one of three treatments - continuous bright light, intermittent bright light or dim light, each of which shifted their sleep-wake cycle one a hour a day over a period of three days
• Participants exposed to continuous bright light shifted their circadian rhythm by 2.1 hours over the course of the study, and those exposed to intermittent bright light saw a shift of 1.5 hours, and the dim light group saw a shift of 0.6 hours
• As a result, participants in the first treatment group felt sleepier two hours earlier in the evening, and woke 2 hours earlier in the morning i.e. closer to the local time conditions they would find after an east-west flight
• Exogenous zeitgebers were able to effect circadian rhythms

Question 28

Exogenous Zeitgbers

Answer 28

Exogenous = outside the organism
Zeitgeber = time-giver

The biological-clock is reset each day by cues in the environment – like the light cues of sunrise and sunset.
This process is called entrainment - the opposite of free-running where the biological clock works free of any exogenous cues, including social cues like clocks.
Therefore, sleeping and wakefulness are determined by an interaction of internal and external factors.
Melatonin - pineal gland
Cortisol - adrenal gland

Question 29

Light as an exogenous zeitgeber

Answer 29

• Light is a key zeitgeber in humans. It can reset the body’s main endogenous pacemaker (the SCN), and thus plays a role in the maintenance of the sleep-wake cycle.
• Receptors in the SCN are sensitive to changes in light levels during the day that they receive from rod and cone cells in the eye via the optic nerve, and use this information to synchronise the activity of the body’s organs and glands.
• Light resets the internal biological clock each day, keeping it on a 24-hour cycle.
• Light also has an indirect influence on key processes in the body that control functions such as hormone secretion (e.g. melatonin and cortisol) and blood circulation.

Question 30

Social cues as exogenous zeitgebers

Answer 30

• Social stimuli, such as mealtimes and social activities, may also have a role as zeitgebers.
• In human infants, the initial sleep-wake cycle is pretty much random. At about 6 weeks of age, the circadian rhythms begin and by about 16 weeks, most babies are entrained. The schedules imposed by parents are likely to be a key influence e.g. adult-determined mealtimes and bedtimes.
• Research also suggests that adapting to local times for eating and sleeping (rather than responding to own feelings of hunger and fatigue) is an effective way of entrainment circadian rhythms and beating jet lag when travelling long distances.

Question 31

Evaluating Exogenous zeitgebers and endogenous pacemakers - weaknesses

Answer 31

1. There are generalisation issues with animal studies to humans - additionally, particularly with Decoursey et al, the ethical issues with the study are open to criticism as animals were exposed to considerable harm, and subsequent risk when returned to their natural habitat
   - Whether what we learn from investigations justifies the aversive procedures involved is a matter of debate, but regardless we cannot be certain that the animal results are externally valid, and so from the research we cannot strongly support the role of the SCN as an endogenous pacemaker
2. The findings of the C&M study have yet to be replicated - other psychologists have also been critical of the manner in which the study was conducted and they have suggested that there may be some limited light exposure to the participant’s eyes which acted as a major confounding variable
   - This suggests results may not be internally valid and as such we cannot strongly support the role of light as an exogenous zeitgeber via the skin through research

Question 32

Evaluating Exogenous zeitgebers and endogenous pacemakers - weaknesses

Answer 32

3. Only in exceptional circumstances are endogenous pacemakers free-running and unaffected by the influence of exogenous zeitgebers - total isolation studies like Siffre’s cave are extremely rare and could be judged as lacking validity for this reason
   - In real-life, pacemakers and zeitgebers interact and it may make little sense to separate the two for the purpose of research

Question 33

Evaluating exogenous zeitgebers and endogenous pacemakers - strengths

Answer 33

1. Decoursey et al, Ralph et al, Campbell and Murphy and Burgess et al
   - Supporting evidence
   - The animal studies emphasise the role of the SCN in establishing and maintaining the circadian sleep-wake cycle
2. Using our knowledge of the importance of light as an exogenous zeitgeber for the sleep-wake cycle, we can use light exposure to avoid jet lag - Burgess et al
   - Real-world application
   - This suggests that the research is externally valid and has potentially important societal implications