Explanations of Other Sleep Disorders
Narcolepsy
Narcolepsy is a disorder where individuals experience sudden and uncontrollable attacks of sleep at irregular and unexpected times, which may last seconds or minutes. An episode is often triggered by stressful situations.
AO1: Explanations of Narcolepsy
A02: Supporting/Contradictory Evidence & Commentary
1.
REM
 Supporting Evidence for REM Explanation
In the 1960s an explanation offered for narcolepsy was that it was caused by a malfunction
P: A strength of the REM explanation of narcolepsy is that supporting evidence has been provided by Vogel (1960).
in the system that regulates REM sleep. This is because one of the classic symptoms of
E: He observed REM sleep at the onset of sleep in narcoleptic patients, whereas it more commonly occurs later in the
narcolepsy is loss of muscle tone (called cataplexy). This is similar to what happens during
first cycle of sleep stages. Further support has been provided by Siegel (1999). He took recordings of neuron activity in
REM sleep. In addition during the daytime, narcoleptics often experience intrusions of REMthe brainstem of narcoleptic dogs. This showed cataplexy (lack of muscle tone) co-occurred with brain cell activity that
type sleep (hallucinations). Furthermore, at night narcoleptics have abnormal REM sleep.
usually only occurs in REM sleep.
E: This is supportive evidence because it provides empirical evidence for the link between cataplexy, REM sleep and
2.
HLA
narcolepsy.
An alternative explanation for narcolepsy was developed in the 1980s. This suggested that
L: As a result, this increases the credibility of the REM explanation of narcolepsy.
narcolepsy was linked to a mutation of the immune system. Honda et al (1983) found
increased frequency of one type of HLA (human leukocyte antigen) in narcoleptic patients.
 Contradictory Evidence for the HLA Explanation
HLA molecules are found on the surface of white blood cells and coordinate the immune
P: A major flaw in the HLA explanation of narcolepsy is that it does not take into account individual differences in
response. Recent research conducted by the Stanford Medical Centre (2012) has found that
sufferers of narcolepsy.
more than 90% of people suffering from narcolepsy with cataplexy have been found to have
E: For example, Mignot et al (1997) argues that the specific HLA variant (HLA-DQB1*0602) found most commonly in
the HLA variant HLA-DQB1*0602.
narcoleptics is not found in all narcoleptics. The same variant is also reasonably common in the general population.
E: Both these findings suggest that the HLA variant cannot be the only cause, perhaps the specific HLA variant may make
3.
Hypocretin
some people vulnerable to suffering narcolepsy; but certain environmental factors (such as stress, diet or brain injury)
Hypocretin is a neurotransmitter than regulates sleep and wakefulness through interactions
may need to be present before the sleep disorder of narcolepsy manifests itself.
with systems that regulate emotion and homeostasis in the hypothalamus (Sakurai, 2007).
L: As a result, this reduces the explanatory power of the HLA explanation of narcolepsy as it suggests the relationship
Normally there are about 10,000 – 20,000 hypocretin-producing cells in the hypothalamus
between the variant and the disorder may be more complex than first thought.
but in many narcoleptics a large number of these cells are missing, resulting in low levels of
hypocretin. This suggests there may be a link between low levels of hypocretin and
 Support for Hypocretin Explanation of Narcolepsy
narcolepsy.
P: A strength of the hypocretin explanation of narcolepsy is that there is a wealth of evidence to support its claims.
E: For example, the first evidence for the hypocretin explanation came from narcoleptic dogs who were found to have a
mutation in a gene on chromosome 12. This mutation had the effect of disrupting the processing of hypocretin (Lin et al,
1999).
E: This provides valuable empirical evidence to support the idea that lower levels of hypocretin may be the cause of
narcolepsy.
L: As a consequence, this increases the reliability of research such as Sakurai (2007) and boosts the credibility of the
hypocretin explanation of narcolepsy as a whole.
AO2: MAID
 Support for Biological Approach
P: One strength of the explanations of narcolepsy is that the methods used to investigate the causes of the sleep
disorder are scientific.
E: For example, Mignot et al (1997) used sophisticated gene sequencing technology to establish a link between
narcolepsy and the HLA variant. Furthermore Siegel (1999) used EEG technology to argue for the REM explanation of
narcolepsy.
E: This means the findings yielded from this type of research are empirical, objective and are falsifiable. This provides
strong supporting evidence for one of the main paradigms in psychology – the biological approach. This is a strength
because they support all the fundamental goals of science which increases the credibility of the narcolepsy explanations
overall.
L: As a consequence, this provides a strong argument for Psychology as a Science.
 Reductionism vs Holism
P: One major issue with the HLA explanation of narcolepsy is that it is reductionist.
E: This is because it reduces complex sleep disorders such as narcolepsy down to low levels of hypocretin in the body.
E: Although this allows for the complex behavior of sleep disorders such as narcolepsy to be understood and studied in a
scientific manner (i.e. genetic sequencing and analysis); it fails to account for other factors that may affect sleep
disorders. For example, Mignot (1998) found that generally narcolepsy does not appear to be inherited. This is indicated
by the fact that narcolepsy does not fun in families and there is no evidence to suggest a genetic concordance rate
between twins. It is more likely that lower levels of hypocretin are not the result of genes but due to brain injury,
infection, diet, stress or possibly the result of an autoimmune attack. None of these factors are considered in the HLA
explanation of narcolepsy.
L: Consequently, this means that the research into narcolepsy is arguably flawed because it does not offer a full account
of the causes of the sleep disorder. Instead, a more holistic view should be considered that encompasses both genetic
and environmental factors.
 Use of Non-Human Animals in Research
P: One main issue with the hypocretin explanation of narcolepsy is that a lot of the supporting studies for the theory are
carried out on animals.
E: For example, Lin et al (1999) used narcoleptic dogs to support the argument that narcolepsy is due to lower levels of
hypocretin.
E: This is an issue because the result may not be extrapolated to humans because biological systems differ considerably
between species and humans are unique.
L: Although it is important to acknowledge that the research provided a good initial starting point for further research
involving humans, the explanatory power and credibility of the hypocretin explanation is reduced as we cannot assume
that there is a link between low hypocretin levels and narcolepsy in humans.
Sleep Walking
Sleep Walking (somnambulism) is a term that covers a range of activities that take place while sleeping but are normally associated with wakefulness (such as eating, getting dressed, or walking about); the person has no conscious knowledge of what they are doing.
AO1: Explanations of Sleep Walking
A02: Supporting/Contradictory Evidence & Commentary
AO2: MAID
1.
Incomplete Arousal
Supporting Evidence: The Diathesis-Stress Model
: Real Life Application
It is thought that sleep walking is a disorder or arousal – a person who is sleep walking is
P: One strength of the incomplete arousal explanation of sleep walking is that support for its assumptions are provided
P: One positive aspect of research into sleep walking is that it has played a pivotal role in some real life applications.
partly awake in the sense that they are engaged in activities normally associated with the
by the Daithesis-Stress Model of sleep walking.
E: This is because research has been used in murder cases where the disorder has been claimed as a defence. Sleep
waking state, but they are also asleep. Most importantly, the kind of sleep they are in is
E: The diathesis-stress model proposed that genes merely provide a vulnerability (diathesis) for a disorder but the
walking experts have offered their views in court.
deep sleep (called slow wave sleep, SWS). This means it is very difficult to rouse the sleep
disorder will only occur in situations of environmental ‘stress’. In the case of sleep walking this seems likely. For example,
E: For example, in October 2003 Jules Lowes from Manchester attacked and killed his elderly father. He claimed that he
walker. Recordings of brain activity made during sleep walking show a mixture of the delta
Zadra et al (2008) studied 40 patients who were referred to the sleep lab for suspected sleep walking. In the sleep lab the
had no recollection of the attack because he was sleep walking at the time. Dr Irshaad Ebrahim, director of the London
waves which are typical of SWS, plus the higher frequency beta waves which are
participants were prevented from falling asleep. On the first night 50% of the sleepwalkers had showed signs of sleep
Sleep Centre, was called in to establish whether what Mr Lowe claimed was true. Tests were conducted by observing Mr
characteristic of the awake state. So it looks as if sleep walking occurs when a person in
walking, which rose to 90% on the second night. Sleep deprivation does not lead to sleep walking in normal individuals.
Lowe while he slept. The tests showed that he was prone to sleep walking and therefore the defence case was proved.
deep sleep is awakened but the arousal of the brain is incomplete.
E: This is supportive evidence because it suggests that the sleep deprivation was acting as a ‘stressor’ in individuals who
However, the judge ruled that the sleep walking was caused by ‘insanity’ and Lowe was sent to a psychiatric hospital for
had a vulnerability for sleep walking. Furthermore the diathesis stress model can be used to explain the higher frequency
an indefinite period of time.
2.
Why Children?
of sleep walking in children. The higher levels of SWS in childhood acts a diathesis, so that children are more likely than
L: This example highlights the importance of sleep walking research and further boosts its credibility as it indicates high
Sleep walking is more common in childhood, one explanation for this it that children have
adults to have episodes of sleep walking.
real life applicability.
more SWS than adults. A recent suggestion by Oliviero (2008) is that the system that
L: As a consequence, this suggests the research into the link between SWS and sleep walking is both reliable and credible.
normally inhibits motor activity in SWS is not sufficiently developed in some children, and it
 Methodological Issue: Low Ecological Validity
also may be undeveloped in some adults. Oliviero (2008) examined the motor excitability of
Commentary on Sleep Walking: Genetic Basis
P: A major flaw with sleep research conducted in a controlled environment is that it lacks ecological validity.
adult sleepwalkers during wakefulness. Compared to normal controls, the sleepwalkers have
P: There is evidence that the tendancy to sleep walk may be inherited.
E: This is because the research is carried out in an artificial and uncomfortable environment. Furthermore, participants
signs of immaturity in the relevant neural circuits.
E: For example, Broughton (1968) found that the prevalence of sleep walking in first degree relatives of an affected
are required to wear electrodes to measure brain wave activity as well as sleep whilst being recorded. Zadra et al (2008)
subject is at least 10 times greater than that in the general population. Twin Studies have also been used; Lecendreux et
induced sleep deprivation in his participants, this is a highly artificial technique to induce stress and would not usually
3.
Risk Factors
al (2003) report about 50% concordance in identical (MZ) twins compared to 10-15% in DZ twins, and also have identified
occur in real life.
Plazzi et al (2005) suggests that certain factors appear to increase the likelihood of sleep
a gene that may be critical in sleep walking (DQB1*05 gene).
E: Although this allows researchers to isolate, manipulate and control for variables, it means that the sleep they are
walking – such as sleep deprivation, alcohol, having a fever, stress or psychiatric conditions.
E: This provides valuable insights into the nature of sleep walking, as well as possibly shedding light on a susceptibility to
investigating may be qualitatively or quantitatively different from sleep in the participants’ natural environment.
Hormonal changes during puberty and menstruation may also be triggers for sleep walking.
sleep walking.
L: As a result, findings from studies such as Zadra et al (2008) be generalised to outside the laboratory setting.
The fact that risk factors trigger sleep walking in only some people suggests that some
L: This increases the credibility of research into the explanations of sleep walking.
Furthermore, this reduces support for the assumption that REM sleep is dreaming sleep.
individuals may have an inherited vulnerability for sleep walking whilst others do not.