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Define biological rhythms

Distinct patterns of changes in body activity (controlled by internal + external factors) that conform to cyclical time periods


What two things are all biological rhythms regulated by?

- Endogenous pacemakers
- Exogenous zeitgebers


What are endogenous pacemakers?

- Internal factors
- Work as an internal body clock to regulate biological rhythms
- E.g. suprachiasmatic nucleus (involved in sleep-wake cycle)


What are exogenous zeitgebers?

- External factors
- Changes in the environment that influence our body clock + rhythms
- E.g. light + social cues (involved in sleep-wake cycle)


What are the three types of biological rhythms?

- Circadian rhythms
- Infradian rhythms
- Ultradian rhythms


Define circadian rhythms

Biological rhythms that occurs in cycles once every 24hrs


What is the example of circadian rhythms we use?

Sleep-wake cycle


What is the sleep-wake cycle?

A circadian rhythm (usually 8 hrs sleep every 24hrs)
Causes us to feel awake/alert in the day and drowsy at night


What exogenous zeitgebers influence the sleep-wake cycle?

- Light
- Social cues


What endogenous pacemakers influence the sleep-wake cycle?

Suprachiasmatic nucleus (SCN)


What is the Suprachiasmatic nucleus (SCN)?

- Endogenous pacemaker involved in the sleep-wake cycle
- Bundle of nerves in the hypothalamus working a an internal body clock


Outline how the SCN works in the sleep-wake cycle?

- Nerve fibres in the eye cross in the optic chiasm
- SCN sits just above the optic chiasm
- SCN detects light in the optic chiasm as its being sent to visual cortex
- SCN sends info to pineal gland about whether its light or dark
- If dark: pineal gland produces melatonin (inducing sleep)
- If light: pineal gland is prohibited from producing melatonin (preventing sleep)


What are two pieces of research on the sleep-wake cycle (circadian rhythm)?

- Siffre (cave study)
- Folkard et al (cave study, changing clock)


Outline Siffre’s cave study 1962 (aim, process, findings, conclusion)

Aim: to see if we have endogenous pacemakers causing our sleep-wake cycle
Process: spent 2 months isolated in a cave - no sunlight or clock
Findings: body chose when to eat and sleep, settled into a sleep-wake cycle of 25-30hrs
- Supports existence of endogenous pacemakers: settled into a regular cycle of approx 25hr day
- Supports existence of exogenous zeitgebers: cycle wasn’t ‘norm’ of 24hrs


Outline Folkard’s cave study 1985 (aim, process, findings, conclusion)

Aim: to see if our internal body clock can be overridden by exogenous zeitgebers
Process: 12 ppts spent 3 weeks in dark cave. Told to go to bed when clock said 11:25pm + wake up at 7:45am. Changed clock to 22hr day.
Findings: Only 1 ppt could comfortably adjust to new regime
Our internal body clock is very strong + it is very hard to override using exogenous zeitgebers


What is the natural length of humans’ sleep-wake cycle?

Slightly over 24hrs


What is the sleep-wake cycle length for humans? Why?

- Naturally slightly longer
- Entrained by exogenous zeitgebers


What happens if the sleep-wake cycle is disrupted?

- Poor health
- Low concentration
- High anxiety


Give 2 positive evaluation points for circadian rhythms

Real world application (shift work)
- Understanding circadian rhythms can help improve conditions for shift workers
- Night shifts can disrupt sleep-wake cycle pattern + cause…
Circadian troughs (reduced conc - usually at 6am)
Poor health (3x more likely to get heart disease)
- Have concluded we should reduce shift work + give readjustment periods
- So, research has helped improve health + conc (+ productivity)

Real world application (medical treatment)
- Understanding circadian rhythms has contributed to chronotherapeutics
- If medicine is given at specific times (corresponding to rhythms) treatment will be more effective
- E.g. rhythms make heart attacks most common in early morning, novel medicine given at 10pm to release early morning, reduced heart attacks
- Understanding bodily rhythms over the day (circadian) improved treatment


Give 2 negative evaluation points for circadian rhythms

Methodological issues with Siffre + Folkard
- Small samples, affected by individual differences
- Sleep-wake cycles may vary by 13hrs-65hrs
- Time when asleep/awake also varies (Duffy’s larks + owls)
- Hard to make generalisable conclusions about circadian rhythms when individual differences are so significant

- Trying to isolate role of endogenous pacemakers + exogenous zeitgebers (e.g. in Siffre’s study on circadian rhythms) is biologically reductionist
- Trying to reduce the cause of rhythms has low ecological validity, as in real life the two causes will never be separated
- So, would be more useful in real world to use an interactionist model, rather than trying to separate the role of internal + external factors


What does it mean to be a ‘lark’?

Wake up early + sleep early


What does it mean to be an ‘owl’?

Wake up late + go to sleep late


Give 2 positive evaluation points for endogenous pacemakers + exogenous zeitgebers

- Supports endogenous: settled into rhythm
- Supports exogenous: rhythm longer than norm (25hrs)
- Both important

Real world application (Shift work)
- Understanding importance of endogenous pacemakers + the issues that come with disrupting the natural sleep-wake cycle has led to improvements in shift work
- Reduced shift work + longer adjustment periods
- Has improved health + concentration of workers


Give 2 negative evaluation points for endogenous pacemakers + exogenous zeitgebers

- Research has tried to isolate two causes (unrealistic + reductionist)
- Need to use interactionist model for conclusions that apply to real world

Research has suggested endogenous pacemakers are still superior
- Limitation of exogenous zeitgebers
- E.g. Miles
Did case study of young blind man (unaffected by light + social cues)
Found strong sleep-wake cycle of 25hrs
- So, endogenous pacemakers are important in keeping biological rhythms + are only slightly entrained (approx 1 hr) by exogenous zeitgebers


What is the piece of research supporting endogenous pacemakers?

- 30 chipmunks
- Looked at endogenous pacemaker SCN
- Destroyed their SCN + let them back into wild to observe for 80 days
- Findings: Sleep-wake cycle disappeared by end of study
Significant proportion killed by predators (because they were awake at unsafe times + hunted)
- Conclusion: SCN is a very important endogenous pacemaker + the sleep-wake cycle cannot exist in the same way without it


What is the piece of research supporting exogenous zeitgebers?

Campbell + Murphy
- Looked at exogenous zeitgeber light
- 15 ppts
- Woke them during sleep + shone torch on back of knees
- Findings: this light could alter sleep-wake cycle by up to 3hrs
- Conclusion: light is an important exogenous zeitgeber as it impacts the natural sleep-wake cycle
(Also - may be other light receptors not just the SCN)


Define infradian rhythms

Biological rhythms that occur less than once every 24hrs


What example of infradian rhythms do we use?

Female menstrual cycle


What is the female menstrual cycle?

An infradian rhythm which occurs over an average of 28days (between the first day of womb shedding/period to the day before the next period) due to changes in hormones over a month


What endogenous pacemakers influence the female menstrual cycle?

- Oestrogen levels rise (ovary develops egg then ovulates)
- Progesterone levels rise after ovulation (womb lining thickens)
- If pregnancy doesn’t occur egg is absorbed + lining breaks down in menstrual flow


What exogenous zeitgebers influence the female menstrual cycle?

- Women synchronising
- Diet/health
- Stress
- Contraceptive pill


Give 2 positive evaluation points for infradian rhythms

Research support
- Stern + McClintock support that infradian rhythms are governed by an endogenous system, affected by exogenous factors
- They focused on the menstrual cycle + affect of women
- 29 female ppts with irregular periods
- Pheromones gathered from 9 women (pad under armpit for 8 hrs) + given to other 20 women (rubbed on upper lip)
- Findings: 68% ppts experienced cycle changes to match ‘odour donor’
- Supports affect of endogenous + exogenous influence on rhythms

Evolutionary advantage of infradian rhythms
- Menstrual cycle (infradian rhythm) can synchronise with other women to get an evolutionary advantage
- In the past, allowed mothers to give birth at same time, so if mothers die in childbirth the orphan can get milk from the social group
- Today, giving birth at same time means help with shared childcare
- Synchronisation may be a valuable theory, showing how infradian rhythms can provide evolutionary benefits


Give 2 negative evaluation points for infradian rhythms

Methodological issues with research
- Research into infradian rhythms (Stern + McClintock) has flaws
- Small sample (29): hard to generalise findings
- Self report (about cycle changes): may lie due to demand c
- Confounding v (stress, diet, etc): may cause change, lowering internal v
- So, supporting research about infradian rhythms may be weak, with flawed conclusions

Issues for the legal system
- PMS (linked to infradian rhythm of menstrual cycle) used as legal defence
- Dalton argued severe PMS is like a mental disorder + individuals cant be held accountable (biological determinism)
- E.g. Ms English - killed married lover, had PMS, manslaughter charge
- Infradian rhythms are seen as biologically deterministic due to the strong role of endogenous pacemakers, causing legal issues


Define ultradian rhythms

Biological rhythms that occur more than once every 24hrs


What is the example of ultradian rhythms we use?

The sleep cycle (stages of sleep)


What is the sleep cycle?

An ultradian rhythm. A continuous 90 min cycle of sleep that repeats during sleep, with each cycle broken into 5 stages.


How long is one sleep cycle?

90 mins


How many sleep cycles does the average person go through each night?



How have we gained our understanding of sleep cycles and the stages of sleep?

EEG recordings


What is Stage 1 of the sleep cycle?

Light sleep where person may be easily woken
- Alpha waves (high frequency, low altitude)


What is Stage 2 of the sleep cycle?

Light sleep where person may be easily woken
- Alpha waves (high frequency, low altitude)
- Some ‘sleep spindles’ (random wave changes - thought to inhibit cognitive functions to allow for sleep)


What is Stage 3 of the sleep cycle?

Deep sleep/slow wave sleep (SWS) where a person is hard to wake
- Delta waves (low frequency, high amplitude)


What is Stage 4 of the sleep cycle?

Deep sleep/slow wave sleep (SWS) where a person is hard to wake
- Delta waves (low frequency, high amplitude)


Which stages of the sleep wake cycle are the same or very similar to each other?

- Stage 1 + 2 (very similar - difference is sleep spindles in 2)
- Stage 3 + 4 (same)


What is Stage 5 of the sleep cycle?

Body is paralysed yet brain is active, resembling an awake brain
- Theta waves
- Eyes move under lids


What is REM?

Rapid Eye Movement
- Associated with dreaming
- In Stage 5 of the sleep cycle


What is NREM?

Non-Rapid Eye Movement
- Not associated with dreaming
- In Stage 1,2,3,4 of the sleep cycle


Give 2 positive evaluation points for ultradian rhythms

Research support
- Dement + Kleitman
- Aim: to measure variations in sleep stages (an ultradian rhythm)
- 9 ppts
- Lab where EEGs recorded during sleep
- Controlled some confounding variables: alcohol, caffeine
- Findings: identified changes in brainwaves that matched 5 stages of sleep + found correlation between REM waves and reports of dreaming
- Research supports the existence of 5 sleep stages + that sleep is an ultradian rhythm because it was recorded multiple times per night

Sleep deprivation
- Problems associated with sleep deprivation support importance of ultradian rhythms such as the sleep cycle
- E.g Randy Gardener
Awake for 264hrs
Blurred vision, disorganised speech, hallucinations
After, he slept for 15hrs
Sleep recovery = 70% Stage 4, 50% Stage 5, little of other stages
- Problems after not sleeping support importance of this rhythm
- Different rates of recovery suggest some stages are even more important for our survival than other (i.e. Stage 4 + REM)


Give 2 negative evaluation points for ultradian rhythms

Methodological issues
- Issues with supporting research methodology (Dement + Kleitman)
- Small sample (9): hard to generalise
- EEGs: Have to make inferences that change in brainwaves means change in stage of sleep (this isn’t a certainty)
- Lab: Lacks ecological validity - may not represent natural sleep pattern
- Flaws in research supporting infradian rhythm of sleep stages may have led to flawed conclusions about these rhythms, low in validity

Individual differences
- The significant variations between people limits ultradian rhythms
- E.g. Tucker et al - found significant differences between peoples’ duration of each stage (particularly 3 + 4). Suggested these were biologically determined
- E.g. Kale + Kale - found differences in each. Older people sleep less (approx 6 hrs)
- So, it is difficult to make a valid theory about ‘normal sleep’ because ultradian rhythms can change between individuals + over time