SLEEP

EEG TODAY Mummy, I Can’t Sleep!

What you need to Know zTwo theories about the function of sleep zWhat happens during sleep and how this might relate to function. zPredictions Generated by each theory zEvidence and evaluation points for each theory zEvaluation using a possible THIRD theory

Objectives Slides 5 – 11 (plus text p148 & 154) z Mini-test zTo know the stages of sleep (1-4 +REM) and brain activity related to each one zTo be clear about the difference between REM and NREM Sleep zTo be able to describe Restoration Theory of sleep with supporting evidence.

Qu. What are the sleep stages? Awake Hours of sleep REM EEG stages

Qu. How do we measure sleep? Electro-encephalogram (Electrical Activity) Electro-oculogram(Eye Movement) Electro-myogram(Muscle tension)

Brain Waves and Sleep Stages

Stages 1 & 2 zRelaxed state – easily woken zHeart rate slows & temperature drops zAlpha & Theta waves zSleep spindles (stage 2) zBrain waves are quite fast

Stages 3&4 Slow Wave Sleep zDeeper Sleep – harder to wake zHeart rate slows further zTemperature keeps dropping zSome slow Delta Waves (50%+ in stage4) zMetabolic rate lowest zGrowth hormone produced

REM Sleep zParadoxical Sleep zBrain active - body paralysed zFaster waves – like waking zIncrease in oxygen consumption, blood flow and neural firing zRapid Eye Movements zHardest to wake from

Qu. Why do we Sleep? sRestoration Model = Sleep allows us to recharge our bodies and recover from fatigue sEvolutionary/circadian rhythm model Sleep’s main purpose is to increase a species’ chances of survival

Objectives – Slides (and text p155) zMini-test zTo evaluate Restoration theory in two ways: zDiscussing supporting and opposing evidence zDiscussing the evidence that relates to the predictions of restoration theory psychlotron.org.uk

Restoration Theory zThe function of sleep is to allow body to be repaired and restored zOswald (1980) zREM essential for brain recovery zSWS essential for body repair psychlotron.org.uk

The importance of SWS zGrowth Hormone is secreted during SWS zSassin et al found that when we sleep during the day and are awake at night the release of GH is also reversed. zThis supports the idea that GH is linked to SWS zKrueger et al (1985) found a link between lack of SWS and reduced immune functioning.

What is different about infant and old people sleep patterns?

Importance of REM sleep zBRAIN DEVELOPMENT zIn babies REM appears to be important for brain growth zLength of REM in a species related to maturity at birth zLess mature at birth = more REM needed zCHECK – who needs more REM – a platypus or a dolphin? zEvaluate: Is this direct evidence?

Importance of REM sleep zNEUROTRANSMITTERS - Siegel and Rogawki (1988) zThere is break in neurotransmitter release zThis allows neurons to regain sensitivity zSupport zMAOI’s increase levels of monoamines (eg serotonin and dopamine) zSide effect – REM is abolished zWhy? Increase in monoamines mean receptors don’t need revitalising zSo – no need for REM (Siegel 2003)

Importance of REM sleep zMEMORY CONSOLIDATION zREM consolidates procedural memory zSWS consolidates semantic memory and episodic memory zStickgold (2005) zEvaluation – Relevant to Restoration Theory? How?

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?

Plenary questions zHow is sleep measured? zWhat does Restoration theory say about the purpose of sleep? zGive two reasons why SWS is important. zWhat distinction does Oswald make about the purposes of REM and SWS? zWhat evidence supports the idea that REM sleep is linked to neurotransmitters?

Restoration theory zMain predictions: yDeficits in functioning during sleep deprivation yRebound following deprivation yIncrease in REM during brain growth, reorganisation & repair yIncrease in SWS during illness, recovery from injury psychlotron.org.uk

Restoration theory zMain predictions: zIncreased Exercise – increased sleep: zShapiro (81) Supports – How? zHorne & Minard (85) opposed – How? psychlotron.org.uk

zPeter Trip Video

Sleep deprivation experiments zPeter Tripp radio DJ sleep deprived self for 200 hours. zRandy Gardner - sleep deprived for 264 hours under supervision of sleep researcher Dement zMay have been getting MICROSLEEP

Rebound zGenerally, people catch up on sleep following deprivation yNot all lost sleep is reclaimed yAbout 70% of lost SWS and about 50% of lost REM typically recovered yOnly REM and SWS sleep is necessary psychlotron.org.uk

Illness & injury zSleep does increase during illness and recovery from injury yTotal sleep time increases during illness yREM increases during recovery from brain injury, ECT & drug withdrawal ySWS deprivation can cause physical symptoms psychlotron.org.uk

Test zWhy does Michael Corke’s story strongly support restoration theory? zWhat Shapiro et al find about the effect of increased exercise? zWhat does the ‘rebound effect’ show about which types of sleep are important? z What is REM sleep important for according to Stickgold?

zMini-test zTo be able to describe evolutionary theory using the ideas of energy conservation, foraging requirements and predator avoidance. zTo understand the theories of Webb and Meddis Objectives – Slides and text p154

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….

MammalHrs of sleep/day Giant Sloth Tree Shrew Cat, Hamster Mouse, rat, squirrel Hedgehog Humans, rabbit, pig Cow, Goat, Elephant Horse, Roe deer 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

Evolutionary Theory of Sleep zTHREE KEY ASPECTS zEnergy Conservation zForaging Requirements zPredator Avoidance (“Waste of Time”)

Webb, (1982) – Energy Conservation zHibernation Theory zSleep evolved to conserve energy zPeriod of enforced inactivity - using less energy (Like hibernation) zImportant for animals with high metabolic rates

Foraging Requirements zSleep limited by food requirements zHerbivores 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. zCarnivores eat more nutritious food so can spend less time foraging  Carnivores generally sleep for longer.

Meddis, (1975) - Predation theory zSleep has evolved to help species adapt to threats. zPatterns of sleep diversify across species due to environmental threats posed, leading to; x Sleep pattern? zLarge predators = zSmall vulnerable animals = zAnimals who cannot see in the dark =

Meddis, (1975) - Predation theory z“Waste of time Hypothesis” zSleep = avoid predators when most vulnerable zMost animals = darkness + hidden zStaying still with nothing better to do zSiegel (2008) being awake is more dangerous zSleep is for energy conservation + avoiding danger zBest strategy for passing on genes = sleep for as long as you can get away with

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

Objectives – Slides and text p155 zMini-test zTo evaluate research on evolutionary theories of sleep zTo Develop an essay plan to answer the likely exam question psychlotron.org.uk

Evidence zSleep patterns are affected by energy expenditure & availability yAnimals generally sleep more when weather is cold and food is scarce (Berger & Phillips, 1995) yHowever, no direct correlation between physical work done and sleep duration in humans (e.g. Horne & Minard, 1985) psychlotron.org.uk

Evidence zComparative studies of different species generally support evolutionary view ySmaller animals tend to sleep more than larger (e.g. giraffe 1hr vs. bat 20hrs) yCarnivores sleep more than herbivores (e.g. lion 16hrs vs. buffalo 3hrs) zSome notable exceptions e.g. rabbit (small, herbivore) & human (much larger, omnivore) both sleep about 8hrs psychlotron.org.uk

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 zWhat is the purpose of sleep according to evolutionary theory? zWhy do differences in the sleep patterns of species of animal support this? zWhat did Meddis claim about the purpose of sleep? zAccording to Webb why do carnivores sleep more than herbivores?

Evolutionary critiques? zQu. Can these ideas be tested? zQu. Does sleep serve the same function for all species? zQu. Is sleep an ‘adaptive process’? zQu. What happens if we are deprived of sleep?

Problems zMany evolutionary significant factors could affect sleep patterns; theory doesn’t tell us which are important yDoes a bat get so much sleep because it’s small or because it has few predators? yWhy do animals with very different lifestyles have similar sleep patterns? psychlotron.org.uk

Problems zSome features of sleep cannot be explained easily by the hibernation theory: yWhy is sleep universal when in some species (e.g. dolphins) it would have been an advantage to get rid of it? yWhy is sleep deprivation apparently fatal? psychlotron.org.uk

RESTORATION OR ADAPTION? Jim Horne (1999) asks…… zQu. If the body can repair itself under a wakeful state, what is the main purpose of sleep, physiological repair or neurotransmitter recovery? zQu. 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 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.

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 night

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?

zHorne (1999) - asks; zQu. What is the point of falling unconscious? zQu. Is sleep is purely restorative, why are there so many variations of sleep patterns across species?

Task zFind 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 zExplain why evolutionary theory contains a contradiction. zWhy is REM sleep a problem when it comes to energy conservation? zWhy can research on different species of animal sometimes be flawed? zWhat is a phylogenetic signal?