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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