Zusammenfassung der Ressource
Theories of Sleep
- Restoration Theory
- 2 stages of sleep -
slow-wave sleep (SWS)
and REM sleep
- REM sleep enables
brain recovery
- SWS enables body repair
- Slow-wave sleep (SWS)
- Growth
hormone is
secreted
during SWS
- growth hormone (GH) stimulates growth
but also enables protein synthesis, cell
growth, and tissue regeneration
- GH is
secreted in
pulses
throughout the
day
- but a significant
amount is
released at night
and mainly during
SWS
- Sassin (1969) - when sleep waking cycles are reversed
by 12 hours, the release of GH is also reversed
- shows that GH release is controlled by neural mechanisms
- The immune
system
- Kreugar (1985) - lack of SWS has
also been associated with reduced
functioning of the immune system
- immune system - consists of various protein
molecules which are regenerated during cell
growth and protein synthesis in SWS
- REM sleep
- Brain growth
- the amount of REM
sleep in any species is
proportional to the
immaturity of the
offspring at birth
- EG. the platypus is immature at birth and
has about 8 hours of REM sleep per day,
whereas the dolphin, which can swim
from birth, has almost no REM sleep
- suggests a
relationship between
neural development
and REM sleep
- Neurotransmitters
- Siegel and Rogawki (1988) -
REM sleep allows for a break in
neurotransmitter release which
permits neurons to regain their
sensitivity and function properly
- REM sleep
and memory
- research on dreams suggests a
link between dreaming and memory
- REM may be important in
the consolidation of
procedural memory,
whereas SWS is important
for the consolidation of
semantic memory and
episodic memory
Anmerkungen:
- - procedural memory
related to skills such as riding a bicycle
- semantic memory
related to knowledge and the meaning of things
- episodic memory
memory for events
- Evaluation -
Restoration Theory
- Sleep deprivation
- Total sleep
deprivation
- various case studies suggest that lack of
sleep doesn't result in ling-term damage
- however, closely-monitored PP's who
have been deprived from sleep for more
than 72 hours display short episodes on
microsleep while they're awake
- EEG recordings
show that
microsleep is
the same as
sleep
- Partial sleep
deprivation
- may lead to
'rebound'
- EG. people awoken
during REM sleep show
up to 50% increases in
REM activity
- same observed when
SWS is prevented
- this rebound effect appears to be related to
REM and SWS which suggests that there
are the 2 kinds of sleep which are vital
- Exercise and the
need to sleep
- if the restoration theory is correct, physical
exercise should lead to increased sleep in
order to restore proteins and biochemicals
- Sharpio (1981) - marathon runners slept for about
an hour more than usual on nights after the race
- however, Horne and Minard (1985) - PP's who were
given numerous exhausting tasks didn't sleep more
than usua. PP's went to sleep faster, but not longer
- Comparative studies
- EEG studies of dolphins have
found no evidence of REM sleep
- if REM sleep is vital to restoration,
why don't dophins need it?
- 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 energy
- hibernation theory
- sleep serves the purpose of
providing a period on enforced
inactivity (using less energy)
- Foraging requirements
- if sleep is a necessity for energy
conservation, the time spent
sleeping may be constrained by
food requirements
- herbivores - spend their time eating
plants, poor in nutrients, need to eat so
can't 'afford' to sleep
- carnivores - eat food high in nutrients,
can 'afford' to rest and conserve energy
- 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
- to be safe they shouldn't sleep at all
but if sleep is a vital function then they
are best to sleep when least vulnerable
- Waste of time
- Meddis (1975) - sleep may simply
ensure that animals stay still when they
have nothing better to do with their time
- Siegel (2008) - being awake is
riskier than sleeping because an
animal is more likely to be injured
- the only possible explanation for
sleep is that it enables both
energy conservation and keeping
an individual out of danger
- EG. the little brown bat is awake for a few
hours each day so it can eat the insects, and
although it's high metabolic rate means it
should eat more than sleep, it can get all it's
food in a few hours so can just spend it's time
sleeping
- Evaluation -
Evolutionary Theory
- Energy
- Zepelin and Rechtschaffen (1974) -
smaller animals with higher
metabolic rates sleep more than
larger animals
- supports the view that
energy conservation might
be the main reason for sleep
- however, sloths
are large animals
and sleep for 20
hours a day
- Foraging and predation
- Capellini (2008) found a
negative relationship between
metabolic rate and sleep
- doesn't support the energy
conservation hypothesis
- animals that sleep in exposed positions sleep less but
sleep time was also reduced in species that sleep socially