Theories on the Function of Sleep

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  • Created by: Hope
  • Created on: 31-05-16 15:37

The Evolutionary Approach: Meddis

Main Premise: Based on the idea that sleep has evolved to allow an organism a greater chance of survival. 


Meddis: SAFTEY 

  • Animals sleep to keep safe
  • Sleep to keep out of harm from predators and when can't see food (sleep when advantageous)
  • Predators sleep for longer as they aren't in danger of being attacked when asleep 
  • Prey are in danger whne they are sleeping, therefore if sleep is vital is should be done when least vulnerable i.e. in the dark 
  • Alos proposed that sleep is what animals do when they have nothing else to do 
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The Evolutionary Approach: Meddis AO2

1) Meddis states that sleep helps to keep animals safe, however sleep makes them vulnerable as they are unconcious and therefore unaware of their surroundings

  • Bentley: If being still and unnoticable great survival tactic why humans so noisy when asleep? If sleep is evolving to help keep us safe, wouldn't it be better to make them alert not vulenerable

2) Support from Allison and Cicchetti: (importance of ecological factors in sleeping patterns)

  • Study looked at sleep patterns across more than 50 species and identified some important correlatios 
    • Predators have more total sleep time than prey 
    • Carnivores sleep for longer than herbivores
    • Animals with safe sleeping sites such as burrows have more sleep
  • AO3: However, this research is limited by the criticism that this may not be due to saftey, instead it may be due to how long the bigger animals need to sleep e.g. Restoration theory 
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The Evolutionary Approach: Meddis AO2/AO3

3) (AO3) Correlational Research 

  • Much of the research in support of the ecological factors mentioned by Meddis are correlational, meaning conclusions cannot be drawn about cause and effect 
  • Also difficult to disentangle the relationships between various factors
    • e.g. predators are by definition carnivores, however not all carnivores are preditors, therefore it may be that predators sleep more because they are carnivores thater than because they are predators 
    • Since small ainnals sleep for longer than large animals to conserve energy it might be this -rather than the safe sleep site - that leads to longer sleep times 

4) Multiple Evolutionary Causes 

  • It is more likely that sleep patterns involve an interaction between several of these evolutionary/ecological factors

IDA - Therefore the theory is not reductionist - takes a complex view and doesn't reduce to one or two factors - HOWEVER, no clear model of why animals have evolved REM and NREM 

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The Evolutionary Approach: Webb


Sleep conserves energy 

  • Sleeping when animals cannot be active saves energy 
  • Warm-blooded animals use eenergy to maintain their temperature 
  • Smaller animals have a higher metabolic rate (uses energy quicker - constantly has to eat)
  • Smaller amimals therefore have to choose whether to sleep or eat to conserve energy 
    • Eating isn't always possible - cant get to food (darkness, predators) so they sleep instead 
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The Evolutionary Approach: Webb AO2

1) Strength: Research evidence from Berger Et Al 

  • Berger states that animal's sleep more when food is scarce (sleeping to conserve energy)

2) Supported by the fact that smaller animals do sleep more than larger animals as they have a higher metabolic rate

  • AO3: However, there are exceptions to this, for example the Lion sleeps up to 20 hours a day 

General IDA) 

The theory is not reductionist - it is more likely that sleep patterns involve an interaction between several of these evolutionary/ecological factors. It takes into account the complexity of sleep patterns and doesn't try to reduce it to one or two simple factors 

However, it does not provide a clear model of why animals have evolved REM and NREM 

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The Restoration Theory on the Function of Sleep

Main Premise: Sleep restores/repairs the body

Sleep has a homestatic function - maintains our bodies by restoring physiological functioning 


Suggested that both REM and NREM sleep serve the purpose of restoring and replenishing brain and body (physiological and psychological)

  • Warched patients with brain damage 
  • Found NREM was needed more for restoring bodily processes that have detoriated or been worn down by the day 
  • REM sleep ins the main time for renewing brain processes and replenishing neurochemicals used up in the day that need to be regenerated by protien synthesis 
    • Brain restoration involves reference to growth hormone and protien synthesis
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The Restoration Theory on the Function of Sleep


  • Researched into sleep deprivation 
  • Similarly to Osborne, suggested that REm and deep NREM were essential for maintaining brain systems 
  • However, argued that light NREM had no function 
  • Also (however), argued that sleep had nothign to do with bodily restoration, this took place during 'relaxed wakefulness'




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Restoration Theory AO2

1) Babies sleep for a lot longer than adults because of the large amount of activity and developing going on in their brain and bodies (Babies sleep for an average of 18 hours a day - half of it in REM, whereas adults only spend 1/4 of their sleep in REM) 

2) Patients with physiological assults on their brain (drug overdoses or ECT) spend an increased amount of time in REM sleep, perhaps to synthesise brain protiens that have been lost or damaged for repair 

3) Support comes from Rechstaffen:

  • Found severe sleep deprivation in rats leads to death 
  • AO3: However, keeping rats awake invovles constant arousal and stress (e.g. they fall into the water if they fall asleep), it may be the stress that is fatal - therefore it is also unethical 
  • Animal studies cannot be generalised to humans - there are psychological differences between rats and humans and therefore sleep needs are different 
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Restoration Theory AO2/IDA

4) Case studies about sleep deprivation: Tripp - New York DJ 'wakeathon', did not sleep for 8 days. Towards the end of the time Tripp showed disturbing symptoms including hallucinations and delusions. Delusions so bad impossible to give him tests to test psychological functioning

However: Dement - Gardner - 17 year old stduent stayed awake for 11 days (Guiness Book of Records). For the last 90 hours he was studied by Dement. He had difficulty performing some tasks however his lack of sleep did not produce any severe disturbances. After, he spent 14 hours and 40 minutes aslep and when he awoke he appeared to have recovered completely. 

AO3 - Both case studies: Male, low population validty (cannot be generalised), individual differences - Gardners age  however, rare! allows us to test things that are unethical 

5) Young: The more we know about sleep patterns the more it indicates that it is environmental not restorational factors that influence the function of sleep. If Oswald correct, then using up energy shoudl lead to extended sleep - research here is not consistent. Also if REM is so important for brain restoration why do some animals not have ti e.g. Dolphins sleep with one hemisphere of the brain off t a tiem and as a result have no REM 

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