Circadian Rhythms - The Sleep-Wake Cycle
Biological Rhythms vary in length.
Circadian Rhythms last about 24 hours. Example: The Sleep-Wake Cycle.
- Michel Siffre investigated the effects on the sleep-wake cycle taking away external cues to see if the 'internal clock' still runs at 24 hours.
- Aschoff and Wever (1986) put participants in underground bunker without external cues and their rhythms settled to 24 to 25 hours.
Studies suggest that circadian rhythms exist without zeitgebers which shows an 'endogenous pacemaker'
However... Czeisler et al. (1999) showed that cycle length varies between 13 to 65 hours.
Circadian Rhythms - Body Temperature
Suggests that body temperature effects cognitive performance.
- It is lowest at 4:30am (36 degrees) and highest at 6:00pm (38 degrees).
- Giesbrecht et al. (1993) placed participants in cold water, they then endured several tasks and those that had lower body temps did worse on the tasks.
- Folkard et al. (1977) studied children being read stories at 9am and 3pm. Children being read stories at 3pm had better long term recall suggesting better cognitive performance when body temperature is highest.
- Hord and Thompson (1983) found no correlation between cognitive performance and body temperature.
However there may be factors that aren't considered, it may be that higher body temperature increases arousal which increases cognitive performance (Yerkes-Dodson 1908).
Infradian Rhythms - The Menstrual Cycle
Infradian Rhythms occur more than 24 hours. E.g. A month.
The Menstrual Cycle regulates ovulation.
The pituitary gland releases hormones - egg is ripened - oestrogen released.
- Russell et al. (1980) studied the synchronisation of women's menstrual cycles. It has been shown that women that live together cycle's synchronise. Swear of one group of women was placed in the upper lip of another group, and eventually their cycles synchronised. This could be because of pheromones which are chemicals produced by a person that only affect the people around them.
- Seasonal Affective Disorder (SAD) low levels of melatonin/serotonin cause depression. More should be produced in winter because of lack of light but if not enough is then you get depressed.
Ultradian Rhythms - Different Stages of Sleep
Ultradian Rhythms are less the 24 hours.
- There are 5 sleep stages.
- The cycle goes for 90 minutes.
- EEGs record brain waves at each stage.
- Awake brain produces Beta Waves.
- NREM sleep: Stages 1 and 2 - Relaxed, easily woken, heart rate slows, temperature drops. Alpha and Theta Waves.
- NREM sleep: Stages 3 and 4 - Metabolic rate slows, growth hormone produced. Delta Waves.
- REM sleep: Brain/eyes active, body paralysed (paradoxical sleep).
In mammels, the pacemaker is the suprachiasmatic nucleus (SCN) which lies in the hypothalamus.
SCN acts as an internal clock which keeps the body at 24 hours.
Is affected by light entering the eyes.
+ light = - melatonin and - light = + melatonin. Melatonin induces sleep.
- Morgan (1995) transplanted the SCNs of mutant hamsters with an abnormal circadian rhythm (20 hours) into normal hamsters who then developed the mutant rhythm.
But... Animal study so lacks external validity and there are ethics involved.
External cues which act as a prompt, and may trigger a biological rhythm.
- Light: Most important zeitgeber. Siffre (1975) stayed in a cave with no light and his internal clock extended to about 25 - 30 hours. Light can reset the SCN.
- Social Cues: Such as meal times and appropriate sleep times. Davidson (2006) says all body cells have their own oscillating rhythms, so cells in the liver and heart are likely to have mealtime rhythms as they are reset by eating.
- Temperature: In the absence of light, may be the dominant zeitgeber.
- Stevens (2006) suggests artificial light disrupts circadian rhythms as it disrupts melatonin production.
Disrupting Biological Rhythms
Shift Work and Shift Lag...
- Decreased alertness: Night workers experience a circadian trough of decreased alertness around midnight when low cortisol levels and 4:00am when body temperature low. (Boivin et al. 1996)
- Sleep Deprivation: Hard to sleep during day due to noise and light etc. So, harder to stay awake at night.
- Those that do shiftwork for more than 15 years are 3 times more likely to develop heart disease (Knutsson et al. 1986) but possibly not a direct link.
- Linked to organ disease (Martino et al. 2008)
- Shift workers experience social disruption (Solomon 1993) divorce rates are up to 60% as they have less time to spend with family.
- Health effects: Insomnia, Anxiety, Irritability, Low energy, Drowsiness.
Jet Travel and Jet Lag
Phase Delay = going back in time (gaining hours) East to West
Phase Disruption = ahead in time (losing hours) West to East
- Winter et al. (2008) takes one day to adjust back to every 1 hour time change.
Sleepiness, lowered concentration, mild depression, headaches, irritability, gastric discomfort, appetite loss.
- Recht et al. (1995) analysed US baseball results over 3 years.
East to West (phase delay) won 44%
West to East (phase disruption) won 37%
Reducing Harmful Shift and Jet Lag Effects
- Gold et al. (1992) non-fluctuating shifts are better because the body can get used to the sleep-wake pattern.
Melatonin: Taken to induce sleep.
Social Customs: Eat at the right times and sleep when the clock says.
- Kripke et al. (2002) study of 1,000,000 men and women.
6/7 hours = reduced mortality.
8 hours = 15% increase. - contradicts theory that lots of sleep
10 hours = 30% increase. correlates with good health.
Sleep Lifespan Changes - Infancy
- 16 hours non-continuous
- Short sleep cycles - wake up about every hour.
- 60 minute cycle (not 90 of an adult)
- Go through active sleep before entering quiet sleep.
6 months: Circadian rhythm established.
1 year: Sleeping mainly at night 1-2 naps.
Sleep Lifespan Changes - Infancy
- adapt for parents: sleeping in day for their benefit.
- Need of being fed regularly, so wake in night.
- Immaturity of brain = greater amount of active sleep.
- 90% of sleep in premature babies is active.
- Supports that younger infants have more active sleep.
Sleep Lifespan Changes - Childhood
- Similar EEG patterns to an adult.
- 12 hours sleep per cycle.
- More REM activity.
- Boys sleep more that girls.
- Parasomnias e.g. night terrors are common.
Sleep Lifespan Changes - Adolescence
- 9/10 hours sleep
- Male REM sleep sometimes accompanied by wet dreams.
- Circadian rhythm changes to phase delay = awake at night more and find it hard to get up.
- Hormones are mainly released at night which can disturb sleep.
- Hormones upset circadian rhythm...responsible for change to phase delay. (Crowley et al. 2007)
- Wolfson and Carskadon (2005) suggest that schools should begin later to accomodate for poor attention span in the morning.
Sleep Lifespan Changes - Adulthood and Old Age
- 8 hours sleep.
- 25% REM sleep. (increased)
- Rare parasomnia but increased insomnia.
- More difficult to sleep, waking 6 times a night.
- Circadian rhythm changes to phase advance = sleeping early, waking early.
- Reduced sleep due to sleep problems or medical problems.
- SWS (deep sleep) reduced in old age... easier to wake.
Functions of Sleep: Restoration Theory
- Oswald (1980) proposed:
- SWS is for body repair. REM is for brain recovery.
Slow Wave Sleep (SWS):
Growth hormone secreted ---> restoration of cells.
Lack of SWS = reduced immune system functioning.
Rapid Eye Movement (REM)
- Higher in babies...more REM, more immature.
- Neurotransmitters 'take a break'.
- Crick and Mitchinson (1983) proposed that during REM sleep, unwanted memories are discarded - so more important memories are easier to access.
Total Sleep Deprivation
In a study participants awake for more than 72 hours fell into 'microsleep'.
(Microsleep - state of sleep but appearing to be awake)
Microsleep has same EEG recordings as sleep.
Apparent non-sleepers (in microsleep) could be getting sleep benefits while appearing to be awake.
MAY HAVE FATAL CONSEQUENCES.
- Rechtschaffen et al. (1983) forced rats to remain physically active on a spinning disk with water below. All died. But could have been due to stress.
Partial Sleep Deprivation
Can lead to REM rebound - need to catch up on REM sleep.
SWS rebound can occur too when EEG shows SWS and participants woken.
- Empson (2002) participants woken when eyes began to dart (REM). On recovery nights, REM amount greatly increased.
Excercise and Sleep:
- Shapiro et al. (1981) found marathon runners slept for 1/2 hours more 2 days after race.
- Horne and Minard (1985) participants given exhausting tasks went to sleep quicker but not for longer.
Functions of Sleep - Evolutionary Explanations
- Webb (1982) Hibernation Theory. Sleep is to conserve energy.
- Predators can sleep for longer than prey.
- Herbivores sleep less than carnivores as they need more time to eat.
Study supporting 'Energy Conservation'
Zepelin and Rechtschaffen (1974) smaller animals with higher metabolic rates sleep more than larger animals.
Study supporting 'Predator Avoidance'
Allison and Ciccetti (1976) species with a higher risk of predatation did sleep less.
Evolutionary Approach: Fails to address why we need more sleep after being deprived. May be a combination of evolutionary reasons and restoration theory.
Initial Insomnia: trouble falling asleep.
Middle Insomnia: trouble staying asleep.
Terminal Insomnia: waking up too early.
Transcient is short-term.
Intermittent is occasional.
Chronic is long-term. (over a month)
Causes of Insomnia
- Occurs on it's own with no single cause.
- May have started due to bad sleeping habits.
- Single underlying cause i.e. Medical
- Could be a characteristic (symptom) of another illness.
Risk Factors For Insomnia
Age: Older people: Other medical problems lead to insomnia.
Gender: Females: Hormonal fluctuations (i.e. menopause)
Parasomnias: Sleep Apnoea (stopping breathing) or sleep walking increase likelihood.
Personality: Keeping problems within inceases likelihood. (Kales et al. 1970)
Watson et al. (2006)
- 50% of the risk could be from genetic factors. (Evidence from twin studies)
Treatment of Insomnia
- Relaxation techniques.
- Increasing 'sleep hygiene'... less caffine, darker room, less naps, more excercise.
- Melatonin intake.
- Reconditioning = bed is just for sleep.
- Sleep Restriction Therapy = gradually increasing sleep time.
Begins in adolescence/adulthood and continues throughout life.
Triggered by strong emotions.
A neurological condition affecting the area of the brain that controls waking and sleeping.
- feeling sleepy all the time
- sleep paralysis
- cataplexy (loss of muscular control in the day)
Explanations of Narcolepsy
Malfunction in system that regulates REM sleep. Explains cataplexy and hallucinations which should only occur in REM sleep.
Honda et al. (1983) found increased frequency of human leukocyte antigen in narcoleptics, HLA molecules are on WBC's surface and co-ordinate immune response.
The most promising lead. Hypocretins play a role in maintaining wakefulness. Lowerlevels in narcoleptics.
REM, HLA, Hypocretin Studies
REM: Siegel (1999)
Brain recordings of dogs shoe cataplexy is linked to activation of cells which are normally only active during REM sleep. REM narcolepsy research has not been convincing.
HLA: Mignot et al. (1997)
Not convincing because HLA increase is found in a lot of the population.
Hypocretin: Nishino et el. (2000) found lower levels in narcoleptics. Unlikely due to inherited factors as doesn't fun in family. Mignot (1998)
May be due to brain injury, infection, stress.
- Affects 20% children.
- Less than 3% adults.
- Occurs in NREM/SWS sleep.
Incomplete Arousal: In sleepwalking, EEG recordings show a mixture of SWS delta waves and beta waves from awake state.
SW occurs when person is woken but brain arousal is incomplete.
Why more in children?
- They have more SWS sleep. SWS not sufficiently developed.
Other Factors in Sleep Walking
- Sleep Deprivation.
- Hormonal changes.
Lecendreux et al. (2003) - used twin studes to show SW can be genetical. Identical twins had 50% concordance. Non-identical had 10-15%.