Theories of sleep

Theories of sleep

1. Sleep - a physical and mental resting state where a person becomes inactive and unaware of the environment

2. Restoration theory

   • Oswald (1966) believed that the function of sleep was to re-group our resources after expending them during the day
     • believed that REM was important for brain growth, and SWS was important for bodily growth
   • during the first year babies sleep 18/24 hours; age 5 an adult circadian pattern is established, may be due to environmental and maturation factors
     • newborn infants spend half the 18 hours in REM, adults spend 1/4 of the 18 hours in REM; babies have to grow more
   • Sassin (1969) found that when sleep-waking cycles are reversed by 12 hours, the release of GH is also reversed
   • also suggested that sleep is an important way of conserving neurotransmitters; through the day, the amount of neurotransmitters in our bodies decreases; REM sleep replenishes neurotransmitters
   • Stickgold (2005) - REM important in the consolidation of procedural memory, SWS important for the consolidation of semonic and episodic memory
   • Jouvet (1967) - when a cat went into REM sleep it's skeletal muscles relaxed, leading it to fall into the water, waking it up; the more deprived of REM sleep the cat was, the more attempts it made to enter REM; the cat eventually died
     • REM is necessary for adequate brain functioning
     • however, cat could've died from stress
   • DJ Peter Tripp - stayed awake for 201 hours; started hallucinating and getting paranoid
     • Randy Gardner - stayed awake for 260 hours; displayed no significant psychotic symptoms
       • however, Randy would've had microsleeps (same as normal sleep)
   • Lavie (1984) studied a 20 y.o whose head was injured by shrapnel; no REM and this had no ill effects

3. Evolutionary theory

   • Energy conservation
     • warm-blooded animals need to expend a lot of energy to maintain a constant body temperature
     • all activities use energy and animals with high metabolic rates use even more
     • hibernation theory
       • sleep serves a purpose of providing a period of enforced inactivity (using less energy)
     • however, Capellini (2008) found a negative relationship between metabolic rate and sleep; doesn't support the energy conservation theory
   • Predator avoidance
     • sleep is constrained by predation risk
     • predators can 'afford' to sleep for longer
     • prey species must remain vigilant so their sleep time is reduced
   • Waste of time
     • Meddis (1975) - sleep may simply ensure that animals stay still when they have nothing better to do
     • Siegel (2008) - being awake may be more riskier than sleeping as an animal could get injured