A2 - Psychology - Theories of sleep
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- Created by: jkav
- Created on: 11-12-15 12:11
Restoration theory - Description
Restoration theory - Description
- SWS for bodily repair and REM sleep is for brain recovery (Oswald).
Slow wave sleep (SWS)
- Growth hormone (GH) is secreted during SWS.
- Amount of GH correlates with amount of SWS (van Cauter and Plat) and if sleep - wake cycle is reversed, GH release swaps to the daytime (Sassin et al).
- SWS helps defence against disease. A lack of SWS impairs the immune system as it uses proteins (antibodies) to fight viruses and bacteria (Krueger et al).
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Restoration theory - Description
Restoration theory - Description
REM sleep
- Babies have relativelymore REM sleep than adults because their brains are growing quickly.
- Animal species born with immature brains need more REM sleep, e.g. platypus (immature at birth) has about eight hours a day whereas a dolphin (more developed at birth) has almost none (Siegel).
- Siegel and Rogawki suggest REM sleep allows neurons to regenerate neurotransmitters.
- MAOI's increase monoamine levels, less need for REM sleep because neurotransmitter levels already increased.
- REM consolidates procedural memories (motor) whereas SWS consolidates semantic (meaning-related) and episodic memories (events) (Stickgold).
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Restoration theory - Evaluation
Restoration theory - Evaluation
- Total sleep deprivation may cause problems, e.g. DJ Peter Tripp (hallucinations and paranoia); however this isn't always true, e.g. Randy Gardner and Hai Ngoc.
- Sleep deprivation for more than 72 hours causes microsleep (Williams et al) so 'non-sleepers' might be benefitting from sleep but appear to be awake.
- Partial sleep deprivation causes a 'rebound', REM (Empson) and SWS (Ferrara et al).
Exercise and the need for sleep
- Shapiro et al did find that marathon runners slept for an hour longer than usual following a race. However, Horne and Minard found participants given exhausting tasks fell asleep faster but didn't sleep for longer.
Comparative studies
- Some species of dolphin have no REM sleep suggesting REM sleep is not vital to restoration.
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Evolutionary theory - Description
Evolutionary theory - Description
Energy conservation
- Warm-blooded animals use energy to maintain a temperature, difficult for small animals because of high metabolic rates.
- The hibernation theory (Webb) suggests that sleep conserves energy because it reduces activity.
Foraging requirements
- Species which eat low energy food like grass (e.g. cows) must spend more time eating so sleep less than ones that eat high energy food like meat (e.g. cats).
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Evolutionary theory - Description
Evolutionary theory - Description
Predator evidence
- A sleeping animal risks being eaten. Predatory species sleep for longer as they are at less risk than prey species.
- For safety's sake species shouldn't sleep at all but sleep when least vulnerable.
Waste of time
- Sleep ensures that animals stay still and safe when they have nothing better to do (Meddis).
- Siegel adds that being awake has the risk of being injured, so animals should sleep for as long as possible - and that is the pattern we see, e.g. little brwon bats.
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Evolutionary theory - Evaluation
Evolutionary theiry - Evaluation
Energy, foraging or predation?
- Smaller species (higher metabolic rates) do sleep more (Zepelin and Rechtschaffen) but there are exceptions.
- Capellini et al found a negative relationships between metabolic rate and sleep, and species sleeping in risky places sleep less but species sleeping in groups ('safety in numbers') also slept less - but shouldn't if predation view is correct.
REM and NREM sleep
- Brain energy use falls in NREM but not REM sleep suggesting only NREM has evolved for energy conservation.
- Allison and Cicchetti found that less NREM but not REM sleep in big animals, fitting this prediction, but Capellini et al found no correlation between body size and REM sleep.
- NREM sleep eveloved first, for energy conservation, and REM sleep later.
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Evolutionary theory - Evaluation
Evolutionary theory - Evaluation
Phylogenetic signal
- Genetically similar mammalian species have similar sleep patterns (Capellini et al).
A combined approach
- Horne: core sleep (SWS) is for resting body and brain and optional sleep (REM and some NREM) occupies unproductive hours and, for small animals, conserves energy.
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