Functions of sleep

EVOLUTIONARY
1. INTRO: Sleep is risky so must have some form of survival value, so can be classed as an advantageous behaviour. WEBB - Sleep is instinctual that has contributed to our survival so has increased our reproductive success.
2. CONSERVATION OF ENERGY
  1. energy is used to maintain body temp so sleep helps offset this demand. Sleep is a time of relative inactivity when energy is conserved.
    1. important for small animals with high metabolic rates so should have evolved to sleep longer to conserve more energy
  2. BERGER & PHILLIPS - +ve correlation metabolic rate and average amount of sleep
  3. SHAPIRO ET AL - only conserves 15% energy but depends on having sufficient energy and lack of disturbances. Dolphins sleep unilaterally so never completely asleep saving energy
3. ESCAPE PREDATORS
  1. status as predator or prey influences amount of sleep. Prey species should have evolved to sleep longer as they are inactive in sleep and less detectable. However, they should also sleep for short periods to prevent being caught.
  2. ALLISON & CICCHETTI - sleep patterns of 39 different species. -ve correlation between risk of predation and amount of sleep
4. METHODOLOGICAL FLAWS - correlational studies, cause and effect. Other factors like body size with explains why prey species sleep more.
5. HOLISTIC - difficult to test that a sleep pattern exists because of evolution, just because it exists doesn't mean it has evolved.
RESTORATION
1. NREM SLEEP - physical restoration
  1. important for repair: use up O2 during wakefulness damaging cells. 'Cell repair hypothesis' states NREM minimises damage caused by free radicals. Brain cells repaired during NREM as brain activity is reduced & brain temp is ideal for enzymes to repair cells.
    1. SWS important for PHYS GROWTH, increase in release of growth hormone enabling protein synthesis and cell growth. SWS also important for IMMUNE FUNCTIONING, antibodies are regenerated defending against bacteria.
2. REM SLEEP- psychological restoration
  1. benefits restoration and reorganisation of CNS and brain development. % of REM much higher in babies supports this. Even higher in premature infants. STERN & MORGANE - believe REM allows brain to replenish NT's used throughout the day. Brain cells are able to regain sensitivity for optimal performance.
  2. JOUVET - cats, REM deprivation. up turned flowerpots on water, cat placed on pot and fell asleep. NREM remained balanced, in REM lost tension and fell in. Learnt to sit wake up when they feel their heads nod. on average survived 35 days without REM.
  3. Human research - PETER TRIPP - NY DJ stayed awake 201 hrs for charity and experienced delusions and hallucinations such as spiders in shoes and thought doctor was an undertaker. RANDY GARDNER, US high school student stayed awake for 264 hrs. In the days following the 11 day period he recovered 50% of REM sleep lost and suffered no long term effects.
    1. METHODOLOGICAL ISSUES: no carefully controlled lab conditions so lacks internal validity. May have experienced periods of 'microscope' such as in shower or if friends fell asleep, so not truly sleep deprived and effects less severe.
3. INTRO: Oswald - purpose of sleep is to restore energy, eliminate waste products, repair cells and recover physical abilities lost during wakefulness.
4. ANIMAL RESEARCH - similar findings across species. Michael Corke stayed awake for 6 months and suffered dementia, hallucinations & rapid weight loss until his organs shut down.

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Functions of sleep

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