SLEEP

Dement and Kleitman (1930’s)

Qu. How do we measure sleep?

Electro-encephalogram (Head)Electro-oculogram (Eye)Electro-myogram (Neck)

EEG TODAY

Brain Waves and Sleep Stages

Qu. What are the sleep stages?

0 1 2 3 4 5 6 7

4

3

2

1

Awake

Hours of sleep

REM

EE

G stages

Qu. Why do we Sleep?

Restoration Model = Sleep allows us to recharge our bodies and recover from fatigueEvolutionary/circadian rhythm model Sleep’s main purpose is to increase a species’ chances of survival

Cognitive model = Sleep is necessary for the consolidation of memory and mental functioning.

Restoration Theory

The function of sleep is to allow body to be repaired and restored

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The importance of SWS

Growth Hormone is secreted during SWSSassin 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 SWS

Krueger et al (1985) found a link between lack of SWS and reduced immune functioning.

What is different about infant and old people sleep patterns?

Oswald

(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.

Siegal and Rogawki (1988)

Sleeping may be a way of conserving & replenishing brain chemicals known as neurotransmitters. Over the day these levels fall. During REM sleep neurons synthesize new neurotransmitter for release during waking.

Siegal (2003)

Some antidepressants which increase levels of monoamines such as dopamine and seratonin abolish REM sleep.

Why might this be?

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?

Restoration theory

Main predictions: Deficits in functioning during sleep

deprivation Rebound following deprivation Increase in REM during brain growth,

reorganisation & repair Increase in SWS during illness, recovery

from injury

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Restoration theory

Main predictions:Increased Exercise – increased sleep:Shapiro (81) Supports – How?Horne & Minard (85) opposed – How?

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Peter Trip Video

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 Dement

May have been getting MICROSLEEP

Sleep deprivation effects

I.Q dropI.Q drop - about 60 studies have confirmed that one hours loss of sleep leads to a 1-point drop in IQ.

Qu. If you skip two hours sleep a night for a week to cram in more revision, how many IQ points will you have dropped?

15 x points - your STM is very poor, you cannot think in complex ways and you loose your flexible thinking for creative answers - you are on auto-pilot.

Rebound

Generally, people catch up on sleep following deprivation Not all lost sleep is reclaimed About 70% of lost SWS and about 50%

of lost REM typically recovered Only REM and SWS sleep is necessary

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Growth & reorganisation

Reduction in sleep over lifespan

Highest in infants; highest REM in early years

Some changes in adolescence

REM

NREM

24 h

ou

r p

eri

od

Age

5yrs

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Illness & injury

Sleep does increase during illness and recovery from injury Total sleep time increases during illness REM increases during recovery from

brain injury, ECT & drug withdrawal SWS deprivation can cause physical

symptoms

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COGNITIVE THEORIES

Empsom and clark (1970)Sleep - especially REM sleep -

facilitates the reinforcement of information in memory.

Qu. What would happen if you were deprived of REM sleep during revision?

Qu. How would you prove the theory right?

Stickgold (1999)

Method: Students taught a visual discrimination task (learning to spot things in their peripheral vision).

They had to do 25 sets in the evening, and another 25 sets in the morning - measured overall improvement.

Some were allowed to sleep normally, others were sleep deprived - some SWS, others REM sleep.

Results: Normal sleep - improved performance 40%Deprived SWS sleep - Improved 28%Deprived REM sleep - improved only 18%

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?

Evolutionary/circadian rhythm model Sleep’s purpose = increase the chances of survival

BRAIN DEVELOPMEN

T

BODY SIZEEcological niche

Species sleep

patterns are

different due to….

Mammal Hrs of sleep/da

y

Giant SlothTree Shrew

Cat, HamsterMouse, rat,

squirrelHedgehog

Humans, rabbit, pig

Cow, Goat, Elephant

Horse, Roe deer

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All mammals and birds sleep.

Qu. Do all animals sleep?

Qu. Can you explain these differences?

Qu. Do whales sleep?

Apparently so

Qu. Do fish sleep?

Apparently so

Fish, reptiles and

amphibians have periods of ‘inactivity’

SWS and REM sleep patterns in mammals

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 =

Lions can do little else but sleep for up to 2 x days after a large

kill

Webb, (1982) - Hibernation theory

Sleep evolved to conserve energyHibernation necessary when food

resource are low.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 generally sleep for longer.

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

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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)

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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.

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?

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?

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?

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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?

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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)?

Horne

(1988) Core sleep consisting of SWS & REM is essential for normal brain functioning. Stages 1-3 NREM sleep are not essential. During core sleep the brain recovers & restores itself, but bodily restoration occurs during optional sleep & periods of relaxed wakefulness.

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?

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.

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?