AO1
Body Restoration
Slow Wave Sleep (SWS)

Growth Hormone
Oswald (1980) proposed that SWS enables the body to repair itself. Growth
hormone is secreted during SWS. Growth hormone (GH) stimulates growth and
is therefore particularly important during childhood. It is also important in
adulthood as it allows the restoration of body tissue, proteins in the body are
fragile and need to be renewed constantly. GH is secreted in pulses during the
day but a significant amount is released at night and mainly in SWS. Sassin et al
(1969) found that when the sleep-wake cycles are reversed by 12 hours (i.e. a
person goes to sleep in the morning and wakes up at night), the release of GH is
also reversed. This shows that GH release is controlled by neural mechanisms
related to SWS. Further evidence comes from research which found that the
amount of GH released correlates with the amount of SWS (Van Cauter and Plat,
1996). Furthermore, the decline in GH in older age has also been associated with
reduced SWS (Van Cauter et al, 2000).

The Immune System
Lack of SWS has also been associated with reduced functioning of the immune
system – the body’s system of defence against infection. The immune system
consists of various protein molecules – antibodies – which are generated during
cell growth and protein synthesis in SWS.
Brain Restoration
REM Sleep

Brain Recovery
Oswald (1980) also argued that REM sleep is responsible for brain recovery as
well as other vital processes in the body. It has been suggested that the amount
of REM sleep in any species is proportional to the immaturity of the offspring at
birth. For example, the platypus is immature at birth and has about 8 hours of
REM sleep per day, whereas the dolphin, which can swim at birth, has almost no
REM sleep (Seigal, 2003). This suggests that there is a relationship between
neural development and REM sleep.

Neurotransmitters
Neurotransmitter activity may be affected by REM sleep. Seigal and Rogawski
(1988) suggest that REM sleep allows for a break in neurotransmitters release
which in turn permits neurons to regain their sensitivity and allow the body to
function properly. Support for this comes from the action of antidepressants
such as MAOIs. These drugs aim to increase the levels of neurotransmitters of
the monoamine group (such as dopamine and serotonin). A side effect is that
MAOIs abolish REM activity completely. One suggestion is that these two effects
are linked – the increase in monoamines means that monoamine receptors don’t
have to be revitalised and therefore there is no need for REM sleep.

REM Sleep and Memory
Crick and Mitchinson (1983) proposed that during REM sleep, unwanted
memories are discarded thus making more important memories accessible. A
recent explosion of research in sleep and memory has found a more complex
relationship (Stickgold, 2005). The evidence currently suggests that REM may be
The Functions of Sleep
1.
Restoration Theory
Commentary
Sleep Deprivation
One strength of the restoration theory as an explanation for the function of sleep
comes from a case study of total sleep deprivation.
For example, Peter Tripp was an American radio DJ who stayed awake for a total
of 201 hours. Three days into the experiment Tripp became unpleasant and
abusive, and after five days he began to hallucinate (seeing spiders in his shoes)
and became paranoid (believing people were drugging his food). Throughout the
experiment Tripp showed a continuous decline in body temperature, and by the
end his waking brain wave patterns were virtually indistinguishable from those of
a sleeping person. After 24 hours of sleep, Tripp awoke and reported himself
feeling perfectly normal.
This is a strength because it provides valuable insight into the potential function
of sleep. The fact that Tripp was hallucinating, paranoid and his body
temperature dropped significantly below normal levels suggests that sleep is
there to help restore our bodies to a normal state (mentally and physically). The
altered state of Tripp’s mind may have been the result of lack of REM sleep and a
subsequent imbalance in neurotransmitters such as mono-amines (serotonin is
known to be linked to ‘happiness’ which may explain why Tripp was irritable).
However, contradictory evidence for the restorative function of sleep comes
from Randy Gardner, an American teenager who managed to stay awake for a
total of 260 hours. During his lengthy period of sleep deprivation he reported no
adverse effects. However he did engage in a prolonged period of sleep after the
experiment was finished.
Consequently, research into sleep deprivation can only provide partial support
for the Restoration Theory of sleep deprivation.
Exercise
A further strength of the restoration theory of sleep is that there is empirical
evidence from exercise studies to support its assumptions.
For example, Shapiro et al (1981) found that runners in a marathon slept for
about an hour more on the two nights following the race, SWS increased in
particular.
This is a strength because it fits the view that NREM sleep appears to be more
associated with physical recovery. For example, it has been established that SWS
allows the restoration of body tissue, proteins in the body must be particularly
depleted and damaged after running 26.3 miles and in desperate need of being
renewed. However, Horne and Minard (1985) gave participants numerous
exhaustive tasks to see if this increased their sleep duration, but it didn’t. The
participants went to sleep faster but did not sleep for longer than usual.
As a consequence, this suggests that the true function of SWS is still unclear and
therefore casts doubt over the credibility of the restorative theory of sleep.
Research using non-human animals
One issue of the restoration theory is that research has been conducted on nonhuman animals that suggests the function of sleep may still be unclear.
For example Rechtschaffen et al (1983) forced rats to remain physically active by
rotating a disc that they were standing on every time the rat started to go to
sleep. After 33 days all sleep-deprived rats had died.
This research is in line with restoration theory as it suggests that without sleep
the rats’ bodies were unable to carry out vital renewel processes (such as
MAID
Case Studies
One issue with the restoration theory of sleep is that the evidence
that supports it is largely based on case studies.
This is an issue because the main difficulty with using case studies
is that the participants are likely to be unique; as a result, we
cannot generalise the findings from such studies to the wider
population.
For example, someone who has difficulty sleeping is less likely to
volunteer for studies, and people who do volunteer are probably
highly motivated to try and cope well with sleep deprivation. This
is demonstrated in the sleep deprivation research. When
comparing the effects of sleep deprivation of Peter Tripp to Randy
Gardner, it can be seen that even two individuals react completely
differently to sleep deprivation.
Therefore, any support for the restoration theory from research
using case studies must be approached with caution, as it cannot
be representative of a wide variety of people.
Contradictory Evidence from the Evolutionary Approach
One major flaw in the restoration theory is that it cannot account
for evidence from research into non-human animals.
For example, the restoration theory cannot account for EEG
studies of dolphins that found no evidence of REM sleep. If REM
sleep is vital for restoration, then why don’t dolphins need it as
well? Furthermore, fur seals sleep one hemisphere at a time when
at sea and have no REM. When back on land they switch to sleep
patterns similar to those of other small mammals.
This is an issue because the evolutionary approach would argue
that these sleep patterns may be related to the process of
evolution – environmental pressures lead to differences in sleep
patterns in different species. Young (2008) suggests that the more
we know about the sleep patterns of other species the more it
becomes apparent that the environmental pressure rather than
restoration provide the key to understanding sleep.
As a result, this casts doubt over the explanatory power of the
restoration theory in its attempt to account for the function of
sleep.
 Non-Human Animal Research
P: One main issue with the research into the restoration theory of
sleep is that a lot of the experiments conducted are carried out on
animals.
E: For example, sleep deprivation research conducted by
Rechtschaffen and Rattenborg used rats and pigeons respectively.
E: This is an issue because the results may not be extrapolated to
humans. Animals such as rats and pigeons differ fundamentally
from humans in many ways. Since a lot of the restoration theory
focuses on brain restoration, how can we apply research from nonhuman animals to humans when their brains differ so dramatically
in terms of size, shape and connectivity. Humans are unique.
important in the consolidation of procedural memory (i.e. riding a bike) whilst
SWS has implications for semantic memory.
releasing GH). However, it has been pointed out that the rats may have died from
the stress of the rotating disc and not sleep deprivation itself. Furthermore more
recent research carried out by Rattenborg et al (2005) on pigeons found that they
suffered no ill effects from continuous sleep deprivation. This suggests that the
function of sleep is still unclear as if restoration theory were correct we should
expect a negative effect on the sleep deprived the pigeons.
2.
AO1
Energy Conservation
Warm blooded animals (mammals), such as ourselves need to expend a lot
of energy to maintain a constant body temperature. This is particularly
problematic for small animals with high metabolic rates, such as mice. All
activities use energy, and animals with high metabolic rates use even more
energy. Sleep, however, serves the purpose of providing a period of reenforced inactivity (therefore using less energy) and so promotes survival by
allowing use to conserve energy for other activities.
Foraging Requirements
If sleep is a necessity, the time spent sleeping may be constrained by food
requirements. An animal has to gather food. Herbivores such as cows and
horses spend their time eating plants (such as grass) that is relatively poor in
nutrients. As a result, they must spend a great deal of time eating, and
consequently cannot afford to spend time sleeping. Carnivores, such as cats
and dogs, eat food that is high in nutrients, and so do not need to eat
continuously. Therefore they can afford to rest much of the time, and by
resting they can conserve energy.
Predator Avoidance
A further likelihood is that sleep is constrained by predation risk. If an
animal is a predator, then it can sleep for longer, whereas for prey species,
their sleep time is reduced as they must remain vigilant to avoid predators.
Logically, to be safe they shouldn’t sleep at all but if sleep is vital, then they
are best to sleep when least vulnerable.
Waste of Time
Meddis (1975) was the first to propose the ‘waste of time’ hypothesis. He
suggested that sleep helps animals to stay out of the way of predators
during the parts of the day when they are most vulnerable. For most
animals, this means sleeping during the hours of darkness. It also means
sleeping in places where they will be hidden. According to Meddis, sleep
Evolutionary (Ecological) Theory
Commentary
The Phylogeny of Sleep Project
One strength of the evolutionary theory of sleep is that we are finding out
about animal sleep habits all the time.
For example Young (2008) reports that out of 5000 mammal species we
have information about the sleep patterns of less than 150. The Phylogeny
of sleep project has found that bats engage in approximately 18 hours of
sleep a day, with 16 of that consisting of NREM sleep. Whereas elephants
sleep for just 3.5 hours a day with an almost equal split between REM and
NREM sleep.
This is a strength of the evolutionary theory of sleep because the most we
know about different animals’ sleep patterns, the stronger the conclusions
we can draw about the true function of sleep. For example, the two animals
compared above is in line with the assumptions of ‘predator avoidance’ as a
function of sleep.
As a result, this increases the credibility of the evolutionary theory as an
explanation of sleep.
Support for Energy Conservation
A further strength of the evolutionary theory is that there is empirical
support to the idea that the function of sleep is to conserve energy.
For example, Zepelin and Rechtschaffen (1974) found that smaller animals
with high metabolic rates sleep more than larger animals.
This is a strength because it supports the view that sleep serves as a period
of in-activity and so energy conservation might be the main reason for sleep.
However, there are many exceptions, such as sloths which are very large yet
sleep for 20 hours a day.
Therefore, because the evidence is not 100% consistent with the
assumptions of energy conservation, this evidence supports the
evolutionary theory to an extent.
L: Consequently, the explanatory power and credibility of the
restoration theory is reduced as we cannot assume people would
react in the same way as animals do to being sleep deprived.
Reductionism
P: One major flaw of restoration theory of sleep is that it is
reductionist.
E: This is because it reduces the complexity of the functions of
sleep simply down to physiological processes in the brain and body
(for example the release of growth hormone and
neurotransmitters such as serotonin).
E: Whilst this allows us to study the function of sleep in great detail
and produce causal theories. It does not consider ecological factors
such as predator-prey status as put forward by the evolutionary
approach to the function of sleep.
L: As a consequence, this reduces the explanatory power of the
restoration theory of sleep. In order to truly understand sleep’s
function, a more interactionist approach must be taken that looks
at both biological and ecological processes of sleep.
MAID
Reliability Issues
One issue with the Phylogeny of Sleep Project is that it has been criticised on
methodological grounds.
This is because it aims to collect data from different sources to help future
understanding of sleep. However, the data is not always reliable.
For example, in some cases there is data for one species from a number of
different studies and the records are conflicting. The various studies of
giraffes rate NREM sleep somewhere between 0.4 and 1.0 hour. The
problem is that often the data is based on studies of fewer than 5 animals
and their sleep has been studied under lab conditions where they may not
be displaying natural behaviour. The animals may also have been observed
for 12 hours.
As a consequence, this reduces the credibility of the Phylogeny of Sleep
Project and casts doubt over the credibility of the evolutionary explanation
as it is supposed to be providing strong empirical evidence for its
assumptions.
Non-human Animal Research
One main issue with the evolutionary explanation of sleep is that the
evidence to support it has been carried out on non-human animal research.
For example, Allison and Cicchetti (1976) conducted research to investigate
predator avoidance as a function of sleep. They found that species who had
a higher risk of predation did sleep less, although again there were
exceptions, such as rabbits who had a very high danger rating yet slept as
much as moles who had a low danger rating.
This is an issue because although it may shed some light on the function of
sleep in non-human animals – we cannot extrapolate the conclusions (that
sleep exists so we can avoid predators) to humans. Humans are completely
unique and are much more complex than the animals involved in the
research. Is it realistic to assume that sleep confers an adaptive advantage in
humans?
Consequently, the explanatory power and credibility of the evolutionary
may simply ensure that animals stay still when they have nothing better to
do with their time.
Seigal points out that in fact, being awake is riskier than sleeping because an
animal is more likely to be injured when it is awake. Seigal’s view, based on
what we currently know about sleep patterns, is that the only possible
explanation for sleep is that it enables both energy conservation and
keeping an individual out of danger.
explanation of sleep is reduced as we cannot assume that the function of
sleep is the same for complex and advanced humans as it is for other nonhuman species.
Reductionist vs Holism
One issue with the evolutionary theory of sleep is that it is reductionist.
This is because it reduces the complexity of sleep purely down to it being an
adaptive behaviour that promotes survival. For example, the evolutionary
approach argues that sleep solely provides the function of aiding survival so
we are able to reproduce and pass on our genes to the next generation.
Whilst this allows for the function of sleep to be studied in great depth (by
looking at non-human animal research); the evolutionary explanation of
sleep does not account for the fact that sleep can have a restorative
function (as put forward by Oswald, 1980).
Perhaps the resolution lies in a combined approach which recognises that
some elements of sleep are for restoration whereas other aspects of sleep
behaviour are related to the function of occupying unproductive hours e.g.
conserving energy in small mammals.