- A cycle that lasts for more than 24 hours, for example, the menstrual cycle and hibernation cycles.
- Pengilly and Admundson blinded squirrels at birth, and kept in the same conditions, kept roughly correct hibernation patterns for 3 years.
- A cycle that occurs approx. every 24 hours, for example the sleep/wake cycle.
- A cycle that occurs less than every 24 hours, for example the REM cycle.
- Dement and Kleitman 9 adults were admitted to a sleep lab, with electrodes attached to their brains. All participants experienced REM, lasting between 3 and 15 minutes, and on average REM occurred every 92 minutes.
Factors Influencing Circadian Rhythms
Endogenous Pacemakers (EP's) - a sort of 'body clock'.
Exogenous Zeitgabers (EZ's) - cues to keep the body clock accurate, such as light or temperature.
Suprachiasmatic Nucleus (SCN) is a group of cells located in the hypothalamus. The cells pulse, or 'fire', rhythmically, similar to the ticking of a clock, however this pulsing speeds up when a person undergoes activity. When removed from the body, but kept alive in fluid, the cells continue to fire. The SCN is located above the cross of the optic nerve, and light that travels through the optic nerve and regulates the SCN.
Pineal Gland - the Pineal Gland is situated in the brain, and is situated near a thin section of the skull, and responds to light that travels through the skull. The Pineal Gland releases melotonin, a hormone that makes you tired. The less light there is, the more melotonin is produced, showing that light affects EP's.
Evidence for the Role of EPs and EZs in the role o
AO1 Silver - removed the SCN from the brains of hamsters, who although retained their normal activities, lost their daily patterns, and performed their activities at erratic times.
AO2/3 Scientific Silver's experiment was a lab experiment, meaning it was well controlled. However, there is a confounding variable, for when removing the SCN, other parts of the hamster's brains may have been damaged. To retaliate, Silver implanted the SCN from foetal hamsters into the brains of the original hamsters. They shortly regained their daily routines, establishing cause and effect. This study also has concurrent validity, and shows the SCN to be the EP.
Animal Research Using animals heightens the amount of control, and lowers the amount of extraneous variables. However, using animals creates ethical problems, as Silver willingly caused harm to the animals. This also caused specieism, and the research cannot be applied to humans. Human evidence would be needed before this research could be applied to humans.
Evidence for the Role of EPs and EZs in the role o
AO1 Siffre - spent 6 months in a Texan cave, measuring his sleep/wake cycle along with his heart rate and breathing. His circadian rhythm went to 25-30 hours, and was steady without the need of external cues. An EZ is needed to keep a "normal cycle."
AO2/3 Case Study The extended CR only happened to one man, so can't be generalised. However, this is a rare insight into the CR so shouldn't be dismissed.
Supporting Evidence Aschoff - participants spent up to a month in underground laboratories, and the regular CR began to drift to 25 hours. However, studies show that artificial light lengthens CR, and in reality it is closer to 24.2 hours rather than 25. However, Miles performed a case study, looking at a man blind from birth, who had a CR of around 24.9 hours, and had to use sedatives and stimulants to control his CR.
Disruption of Biological Rhythms - Shift work
AO1 Shift Work - people end up working when they should sleep, interrupting their normal cycle. When a shift changes, it requires a person to adapt to a new pattern, disrupting links between EZ and biological rhythms. Biological rhythms can adapt at different speeds, leaving a person internally desynchronised for days. It is important to minimalist disruption. Forwards shift patterns (working with longer days) are better than backwards shift patterns (working with shorter days).
Czeisler - A study of a chemical plant in Utah, where a backwards shift pattern was already in place. This pattern seemed to causes sleepiness and stress. Czeisler suggested a forward shift pattern that changed every 3 weeks, giving the workers time to adjust. The shift pattern changed for 130 workers, and after less 9 months the workers reported to be less tired and more productive.
Disruption of Biological Rhythms - Shift Work (con
AO2/3 Methodology Large sample used in a realistic environment, so ecologically valid. Gender biased as only men used, workers may have felt better when researchers gave them extra attention, however it is an ethical way of testing testing shift work.
Supporting Evidence - Phillips - found same results when permanent shift was introduced, where workers were given the choice of early, late or night shifts, allowing the body to adjust to the shift change. However, it was less popular as not many favoured permanent night shifts.
Disruption of Biological Rhythms - Jet Lag
AO1 Jet Lag is caused by rapid travel across time zones, which lasts until the body resynchronizes. Klein found that there would be less jet lag from travelling east to west than travelling west to east, as days are lengthened rather than shortened. Recht, Lew and Schwarte studied baseball teams from the East and West coasts of the USA. The East coast teams that travelled West won 44% of their games, and West coast teams that travelled East only won 37% of their games over a period of 3 years.
AO2/3 Methodology - no ethical issues, high ecological validity, although there may be extraneous variables. East coast teams may have generally been better, although this should have evened out over 3 years. The study is scientific and objective.
Practical Applications - this study can help people minimalism disruption, and to prevent jet lag local times should be adopted and person should spend day in sunlight. The USA use melotonin tablets, which aren't available in the UK, due to possible side effects.
Stages of Sleep
Stage 1 - transition between wake and sleep, eyes roll slightly and Theta waves show on EEG.
Stage 2 - Theta waves still present along with sleep spindles.
Stage 3 - amount of sleep spindles decrease, Delta waves appear.
Stage 4 - mainly large, slow Delta waves, this is the deepest stage of sleep.
REM - EEG shows wake-like state, muscles lose tone, eyes move, heart rate and blood pressure increase, possibility of sexual arousal, difficult to wake, known as "paradoxical sleep" as person is active despite being asleep.
After 15 minutes in REM, move back to stage 2, then down to stage 4. Repeats on a 90 minute cycle.
Dement and Kleitman - REM is associated with dreaming, when woken during REM, dreaming was reported 80% of the time, when woken during NREM dreaming was reported 20% of the time.
Locus Coeruleus Raphe Nucleu
Lifespan Changes in Sleep
Premature Babies - 80% REM
Babies - 16-20 hours sleep, 50% REM, during 1st year sleep pattern regulates.
1 yr - 6-8 hours night sleep, 1-2 hours of day naps, 25% REM
5 yrs - 8 hours sleep, 5.8 stage 1, 47% stage 2, 24% stage 3 + 4, 25% REM.
30 yrs - Reduction of REM
70 yrs - 6 hours sleep, 6.8% stage 1, 55% stage 2, 9% stage 3 + 4, 19% REM.
Males: More sleep hours, deep sleep and REM. Females: more stage 2, less sleep hours, deep sleep and REM.
REM is used for growth and repair. Decrease in sleep efficiency as age increases, REM decreases by 0.6% each decade.
Lifespan Changes in Sleep (cont.)
AO2/3 Methodological Problems - the equipment used to measure sleep may disturb sleep quantity and quality.
External Factors - work, children, aches and pains, medication and sharing a bed can affect sleep.
Individual Differences - sleep varies night to night, the Mediterranean and South Americans have siestas, Greece and China use polyphasic sleep.
Evoloutionary Theory of Sleep
AO1 Selective Advantages behaviour that is desirable is passed on through mating, such as desirable sleep patterns.
Ecological Niches living conditions, such as habitat, predator/prey, nocturnal etc...
Meddis - Predator-Prey status, sleep keeps prey safe when they cant continue regular activities.
Webb - Hibernation theory - hibernate to conserve energy when activities become impossible, such as foraging, good for animals with higher metabolic rates,
Evoloutionary Theory of Sleep (cont.)
AO2/3 Allison and Cicchetti - studied 39 species, found prey slept less, as sleep could be dangerous. Herbivores (prey) sleep less than carnivores. Sleep leaves prey vulnerable. Non-human animals - ethical issues, observation may disturb animals, captivity animals may behave differently.
Lima and Rattenborg - Base Metabolism Rate (BMR) is positively correlated with sleep time, smaller animals have higher BMR. Only NREM sleep conserves energy.
Lesku - BMR is negatively correlated with NREM, contradiction, however BMR could be measured differently between researchers.
However, this research relies on other correlations, such as body weight/sleep time, cant establish cause and effect, eg small animals may find it easier to find places to sleep.
Behaviour may not have evolutionary advantage, may just be a neutral behaviour.
AO1 Oswald - brain trauma patients spent more time in REM, whereas new skin cells grow quicker during deep NREM, suggesting REM is for brain restoration and NREM is for body restoration.
Horne - REM and deep NREM (known as core sleep) is essential for normal brain function, whereas light NREM serves no real function. As we enter NREM, there is more growth hormone released, however, hormone needs protein and amino acids for tissue repair, and by the time we sleep, nutrients from the meal have been absorbed. Body repair may occur during "relaxed wakefulness" (after a big meal), rather than during sleep.
AO2/3 Peter Tripp USA DJ, stayed awake for 201 hours, suffered from hallucinations, paranoia and delusions. Afterwards, slept solidly for 24 hours and felt normal, however personality changed, and he lost his job and wife, could be down to sleep deprivation, alternatively could be other factors. Little control, Tripp may have had "micro-sleep", non-human studies show deprivation can lead to death, eg, rats die after 19 days of no sleep, although it could be down to stress.
Restoration Theory (cont.)
AO2/3 High REM in Babies as brain and synaptic connections are being made. Lab studies shows deprivation of REM can lead to REM rebound, thus supporting the theory. Patients on anti-depressants have less REM and no REM rebound when they stop taking anti-depressants, however the drugs increase the levels of neurotransmitters. Stern and Morgane linked REM to making neurotransmitters, with drugs there is less need for REM, supporting the theory.
Horne and Pettitt - lab experiment where participants where deprived of sleep, and some were given incentives to complete a task, whereas others were given no incentives. Incentives overcame the effects of sleep deprivation, although it eventually affected cognitive performance. Participants recovered after 8 hours of sleep. Difficult to generalise as participants may have had "micro-sleep". Restoration theory leads to specific hypothesis that can be tested, in order to see if the theory is reliable.
Sleep Disorders - Insomnia
AO1 Patients suffer with quality and duration of sleep, leads to day time sleepiness and problem functioning. Symptoms - sleep onset latency of > 30 mins, sleep efficiency of < 85%, and night time awakenings.
Explanation 1 - (primary insomnia: no other condition apparent, idiopathic insomnia can last for entire life.) Brain centres use neurotransmitters, malfunction in system can cause disrupted sleep pattern and insomnia. Winkleman - found those with insomnia for 6 months have reduced levels of GABA (reduces brain activity, a neurotransmitter, helps 'shut off brain').
Explanation 2 - (secondary insomnia: linked to another condition.) Conditions such as depression, anxiety and sz can be linked with insomnia. Morin - 40% of insomniacs have other conditions, anti-psychotics may cause insomnia, those with anxiety issues may stay up worrying.
Sleep Disorders - Insomnia (cont.)
AO2/3 1) Highly reductionist theory, doesn't take other factors into account, there is a high level of comorbidity between insomnia and anxiety, suggesting other factors are involved. Effectiveness of treatment can suggest cause. Insomniacs are often anxious before bed about sleep, and their functioning. CBT reduces worries and is often successful. Stimulus control therapy based on learned response teachers new cues to change behaviour, eg only going to bed when tired, can be effective.
2) Research - Gregory, longitudinal study on relationship between family conflict and insomnia. New Zealand children were followed from birth in 1972 to the present day, correlation was found between conflict when aged 9-15 and insomnia at age 18. Cause and effect can't be established, other factors such as personality may affect conflict, study was assessed with questionnaires which can lead to social desirability bias, study is culture biased.
3) Difficult to isolate key variables in secondary insomnia, other disorders may be symptoms of insomnia, rather than the cause. Has implications on treatment, quality of life may still be affected.
Sleep Disorders - Sleepwalking
AO1 parasomnia, doesn't result in daytime sleepiness, occurs in deeper stages of NREM, often perform automatic tasks, usually have no recollection.
Explanation 1 - Can run in families, genetic involvement, Baker - higher concordance rates in mz than dz twins. Delay in development, movement centres in brain usually inhibited during sleep, childhood sleepwalking suggest under developed inhibitory circuits.
Explanation 2 - psycho-dynamic approach suggests acting out conflicts in repressed unconscious during sleep walking, returning to childhood 'safe place' - Dreams work through unconscious anxieties, REM-NREM stops this causing sleep walking.
Sleep Disorders - Sleepwalking (cont.)
AO2/3 1) Concordance rates for mz twins aren't 100%, so other factors must be present. Delay in development doesn't explain 3% sleepwalking adults. Could use diathesis stress model.
2) Free will - people can commit violent crime whilst sleepwalking, they have no free-will (on 'autopilot'). No responsibility, so cannot be guilty if person has clear clear history of sleepwalking.
3) Psycho-dynamic theory is untestable, no scientific evidence.
Sleep Disorders - Narcolepsy
AO1 1 in 2000 suffer from extreme daytime sleepiness, cataplexy, hypnagogic hallucinations, sleep paralysis.
Explanation 1 - brain damage, Von Economo - patients with damage to hypothalamus have similar symptoms to narcolepsy. Brain damage can affect cells that secrete orexin (hormone linked to narcolepsy).
Explanation 2- Lin - dogs go straight into REM and have tendency towards cataplexy, linked to gene defect on chromosome 12. 12 is responsible for regulating orexin, defect means it cannot perform normal function. Thanaickal - narcoleptics have reduced orexin creating cells in hypothalamus. Administration of orexin directly into locus coerellus increases wakefulness in rats.
Sleep DIsorders - Narcolepsy (cont.)
AO2/3 1) Case study on a 16 year old girl, who developed narcolepsy after damage to hypothalamus after a tumour was removed. Lower level of orexin was found. Arii - removal of tumour damaged orexin secreting cells. Can't generalise, removal could've damaged other areas, and there are confounding variables.
2) Animal research - can't generalise. Overeem - found gene on chromosome 6 that is linked with narcolepsy, supporting genetic involvement. Gene helps regulate immune system, orexin cells destroyed when system goes wrong. One mutatation is associated with narcolepsy, but not all sufferers have mutation and vice versa. Details of link still to be uncovered.
3) Focuses on nature not nurture. Mignot - concordance rates in mz twins are 25%, must be environmental factors, could use diathesis stress model.