What you need to Know Two theories about the function of sleep What happens during sleep and how this might relate to function Predictions Generated by each theory Evidence and evaluation points for each theory ID: 738217
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Slide1
SLEEPSlide2
EEG TODAY
Mummy, I Can’t Sleep!Slide3
What you need to Know
Two theories about the function of sleep
What happens during sleep and how this might relate to function.Predictions Generated by each theoryEvidence and evaluation points for each theoryEvaluation using a possible THIRD theorySlide4
Objectives
Slides 5 – 11 (plus text p148 & 154)
Mini-testTo know the stages of sleep (1-4 +REM) and brain activity related to each oneTo be clear about the difference between REM and NREM SleepTo be able to describe Restoration Theory of sleep with supporting evidence.Slide5
Qu. What are the sleep stages
?
0
1
2
3
4
5
6
7
4
3
2
1
Awake
Hours of sleep
REM
EEG stagesSlide6
Qu. How do we measure sleep?
Electro-encephalogram (
Electrical Activity
)
Electro-oculogram (
Eye Movement
)
Electro-myogram (
Muscle tension
)Slide7
Brain Waves and Sleep Stages
Slide8
Stages 1 & 2
Relaxed state – easily woken
Heart rate slows & temperature dropsAlpha & Theta wavesSleep spindles (stage 2)Brain waves are quite fastSlide9
Stages 3&4 Slow Wave Sleep
Deeper Sleep – harder to wake
Heart rate slows furtherTemperature keeps droppingSome slow Delta Waves (50%+ in stage4)Metabolic rate lowestGrowth hormone producedSlide10
REM Sleep
Paradoxical Sleep
Brain active - body paralysedFaster waves – like wakingIncrease in oxygen consumption, blood flow and neural firingRapid Eye MovementsHardest to wake fromSlide11
Qu. Why do we Sleep?
Restoration Model
= Sleep allows us to recharge our bodies and recover from fatigue
Evolutionary/circadian rhythm model
Sleep’s main purpose is to increase a species’ chances of survivalSlide12
Objectives –
Slides 13- 27(and text p155)
Mini-testTo evaluate Restoration theory in two ways:Discussing supporting and opposing evidenceDiscussing the evidence that relates to the predictions of restoration theory
psychlotron.org.ukSlide13
Restoration Theory
The function of sleep is to allow body to be repaired and restored
Oswald (1980)REM essential for brain recoverySWS essential for body repair
psychlotron.org.ukSlide14
The importance of SWS
Growth Hormone is secreted during SWS
Sassin et al found that when we sleep during the day and are awake at night the release of GH is also reversed. This supports the idea that GH is linked to SWSKrueger et al (1985) found a link between lack of SWS and reduced immune functioning. Slide15
What is different about infant and old people sleep patterns?Slide16
Importance of REM sleep
BRAIN DEVELOPMENT
In babies REM appears to be important for brain growthLength of REM in a species related to maturity at birthLess mature at birth = more REM neededCHECK – who needs more REM – a platypus or a dolphin?
Evaluate: Is this direct evidence?Slide17
Importance of REM sleep
NEUROTRANSMITTERS - Siegel and
Rogawki (1988)There is break in neurotransmitter releaseThis allows neurons to regain sensitivitySupport
MAOI’s increase levels of monoamines (
eg
serotonin and dopamine)Side effect – REM is abolishedWhy? Increase in monoamines mean receptors don’t need revitalising So – no need for REM (Siegel 2003)Slide18
Importance of REM sleep
MEMORY CONSOLIDATION
REM consolidates procedural memorySWS consolidates semantic memory and episodic memoryStickgold (2005)Evaluation – Relevant to Restoration Theory? How?Slide19
Oswald – Supporting evidence
(1983) Found that tissue growth in skin takes place more quickly when we are asleep. REM sleep is important for brain growth & repair. SWS important for bodily growth & repair.
(1969) Patients recovering from drug overdoses. Significant increase in quantity of REM sleep which is indicative of recovery processes.
EVALUATE- other possible conclusions?Slide20
Plenary questions
How is sleep measured?
What does Restoration theory say about the purpose of sleep?Give two reasons why SWS is important.What distinction does Oswald make about the purposes of REM and SWS?What evidence supports the idea that REM sleep is linked to neurotransmitters?Slide21
Restoration theory
Main predictions:
Deficits in functioning during sleep deprivationRebound following deprivationIncrease in REM during brain growth, reorganisation & repairIncrease in SWS during illness, recovery from injury
psychlotron.org.ukSlide22
Restoration theory
Main predictions:
Increased Exercise – increased sleep:Shapiro (81) Supports – How?Horne & Minard (85) opposed – How?
psychlotron.org.ukSlide23
Peter Trip VideoSlide24
Sleep deprivation experiments
Peter Tripp
radio DJ sleep deprived self for 200 hours. Randy Gardner - sleep deprived for 264 hours under supervision of sleep researcher DementMay have been getting MICROSLEEPSlide25
Rebound
Generally, people catch up on sleep following deprivation
Not all lost sleep is reclaimedAbout 70% of lost SWS and about 50% of lost REM typically recoveredOnly REM and SWS sleep is necessary
psychlotron.org.ukSlide26
Illness & injury
Sleep does increase during illness and recovery from injury
Total sleep time increases during illnessREM increases during recovery from brain injury, ECT & drug withdrawalSWS deprivation can cause physical symptoms
psychlotron.org.ukSlide27
Test
Why does Michael Corke’s story strongly support restoration theory?
What Shapiro et al find about the effect of increased exercise?What does the ‘rebound effect’ show about which types of sleep are important? What is REM sleep important for according to Stickgold?Slide28
Mini-test
To be able to describe evolutionary theory using the ideas of energy conservation, foraging requirements and predator avoidance.To understand the theories of Webb and Meddis
Objectives – Slides 29- 39and text p154Slide29
Evolutionary/circadian rhythm model
Sleep’s purpose = increase the chances of survival
BRAIN DEVELOPMENT
BODY SIZE
Ecological niche
Species sleep patterns are different due to….Slide30
Mammal
Hrs of sleep/day
Giant Sloth
Tree Shrew
Cat, Hamster
Mouse, rat, squirrel
Hedgehog
Humans, rabbit, pig
Cow, Goat, Elephant
Horse, Roe deer
20
15
14
13
10
8
3
2
2
All
mammals and birds sleep.
Qu. Do all animals sleep?
Qu. Can you explain these differences?Slide31
Qu. Do whales sleep?
Apparently soSlide32
Qu. Do fish sleep?
Apparently so
Fish, reptiles and amphibians have periods of ‘inactivity’Slide33
SWS and REM sleep patterns in mammalsSlide34
Evolutionary Theory of Sleep
THREE KEY ASPECTS
Energy ConservationForaging RequirementsPredator Avoidance (“Waste of Time”)Slide35
Webb, (1982) –
Energy Conservation
Hibernation TheorySleep evolved to conserve energyPeriod of enforced inactivity - using less energy (Like hibernation)Important for animals with high metabolic ratesSlide36
Foraging Requirements
Sleep limited by food requirements
Herbivores tend to eat large quantities of low nutrition food e.g grass and therefore need to eat a lot of the time – less time for sleep.Carnivores eat more nutritious food so can spend less time foragingCarnivores generally sleep for longer.Slide37
Meddis, (1975) -
Predation theory
Sleep has evolved to help species adapt to threats.Patterns of sleep diversify across species due to environmental threats posed, leading to;
Sleep pattern?
Large predators =
Small vulnerable animals = Animals who cannot see in the dark = Slide38
Meddis, (1975) -
Predation theory
“Waste of time Hypothesis”Sleep = avoid predators when most vulnerableMost animals = darkness + hiddenStaying still with nothing better to doSiegel (2008) being awake is more dangerous
Sleep is for energy conservation + avoiding danger
Best strategy for passing on genes = sleep for as long as you can get away withSlide39
Lions can do little else but sleep for up to 2 days after a large killSlide40
Objectives –
Slides 42-54and text p155
Mini-testTo evaluate research on evolutionary theories of sleepTo Develop an essay plan to answer the likely exam question
psychlotron.org.ukSlide41
Evidence
Sleep patterns are affected by energy expenditure & availability
Animals generally sleep more when weather is cold and food is scarce (Berger & Phillips, 1995)However, no direct correlation between physical work done and sleep duration in humans (e.g. Horne & Minard, 1985)
psychlotron.org.ukSlide42
Evidence
Comparative studies of different species generally support evolutionary view
Smaller animals tend to sleep more than larger (e.g. giraffe 1hr vs. bat 20hrs)Carnivores sleep more than herbivores (e.g. lion 16hrs vs. buffalo 3hrs)Some notable exceptions e.g. rabbit (small, herbivore) & human (much larger, omnivore) both sleep about 8hrs
psychlotron.org.ukSlide43
Energy consumption issues?
Marine mammals do not show REM sleep, perhaps because relaxed muscles are incompatible with the need to come to the surface to breathe.In dolphins and birds, only one brain hemisphere enters SWS at a time— the other remains awake.Slide44
Test
What is the purpose of sleep according to evolutionary theory?
Why do differences in the sleep patterns of species of animal support this?What did Meddis claim about the purpose of sleep?According to Webb why do carnivores sleep more than herbivores?Slide45
Evolutionary critiques?
Qu. Can these ideas be tested?
Qu. Does sleep serve the same function for all species? Qu. Is sleep an ‘adaptive process’?Qu. What happens if we are deprived of sleep?Slide46
Problems
Many evolutionary significant factors could affect sleep patterns; theory doesn’t tell us which are important
Does a bat get so much sleep because it’s small or because it has few predators?Why do animals with very different lifestyles have similar sleep patterns?
psychlotron.org.ukSlide47
Problems
Some features of sleep cannot be explained easily by the hibernation theory:
Why is sleep universal when in some species (e.g. dolphins) it would have been an advantage to get rid of it?Why is sleep deprivation apparently fatal?
psychlotron.org.ukSlide48
RESTORATION OR ADAPTION?
Jim Horne
(1999) asks……Qu. If the body can repair itself under a wakeful state, what is the main purpose of sleep, physiological repair or neurotransmitter recovery?Qu. If REM is for neurotransmitter recovery, why do infants spend 50% of their sleep in REM, but by the first year they have half of that (when most learning occurs)?Slide49
Horne
(1988) Core sleep consisting of SWS is essential for normal brain functioning. Stages 1-3 NREM and REM sleep are not essential. During core sleep the brain recovers & restores itself, but bodily restoration occurs during optional sleep & periods of relaxed wakefulness.Slide50
Horne
(1997) SWS (more dominant in the first 6 hours of sleep) is biologically essential.
In sleep labs participants deprived of sleep for 72 hours only needed 8 hours to restore powers of concentration. Most of the 8 hours is spent in SWS.People adapt to less sleep by sleeping more efficiently – going to sleep faster, entering deep sleep faster and waking less in nightSlide51
Horne
(1997) SWS (more dominant in the first 6 hours of sleep) is biologically essential.
EVALUATE HORNE’S METHOD AND FINDINGS – how convincing are his conclusions?Slide52
Horne (1999) - asks;
Qu
. What is the point of falling unconscious?Qu. Is sleep is purely restorative, why are there so many variations of sleep patterns across species?Slide53
Task
Find one supporting and one opposing piece of evidence for each of the evolutionary purposes of sleep – use page 154 to 155 and write down your findings.Slide54
Test
Explain why evolutionary theory contains a contradiction.
Why is REM sleep a problem when it comes to energy conservation?Why can research on different species of animal sometimes be flawed?What is a phylogenetic signal?