Outline and evaluate sleep walking as a sleep disorder (8+16)

Sleep walking is a parasomnia in which an individual engages in activities normally characterised by the awake brain. This is most common in childhood, affecting 20% of children and less than 3% of adults. It most commonly occurs during NREM and slow wave sleep (SWS). It is believed to be a disorder related to arousal with EEG recording during sleep walking showing a mixture of delta waves, typical of SWS, but also beta waves, characteristic of the awake brain. Theories propose it occurs when a person in SWS is woken but arousal in the brain is incomplete therefore causing the disorder.

Another explanation suggests sleep walking is a developmental disorder. It is suggesting that the system that normally reduces motor activity in SWS is not sufficiently developed in some children and it also may be underdeveloped in some adults causing the disorder. 

Sleep walking can be explained using the diathesis-stress model which proposes that a genetic vulnerability may be the underlying cause. But, sufficient environmental triggers are needed to trigger the disorder. Other medical disorders such as fever, asthma, seizures, sleep apnoea and psychiatric disorders have been linked to sleep walking suggesting it may be the cause of a symptom of another underlying problem.

Broughton et al found it is ten times more likely for sleep walking to occur if a first degree relative has a history of sleep walking, compared to the general population, supported in twin studies and close family members both showing sleep walking, providing evidence of a genetic link for the disorder. However, sleep walking will not always despite a genetic vulnerability. Therefore environmental factors likely influence sleep walking e.g. stress, alcohol and sleep deprivation have been linked to sleep walking. This provides support for the diathesis-stress model and highlights how nature and nurture may interact causing an individual with a genetic vulnerability yo show the disorder.

Lecendreux et al reported a 50% concordance rate in MZ twins showing sleep walking compared to 10-15% in DZ twins suggesting a genetic link. This also highlights the importance of environmental influences as MZ twins did not have 100% concordance, suggesting the environment plays a mitigating role. MZ twins likely experience similar environmental influences due to them looking similar. This may have an influence on psychological development causing them to develop similar disorders due to being treated similarly by those around them. However, twin studies may lack external validity as twins will experience different environmental factors than the rest of the population therefore results may not be generalisable to the population therefore results may not be generalisable and findings may not explain how others develop sleep walking. 

Understanding sleep walking has real world application. In some cases it has been used as legal defence for murder. Therefore it is important to establish the level of control an individual has while sleep walking. In one case Jules Low attacked and killed his elderly father, citing sleep walking as a defence. He was ultimately acquitted after tests showed he had a tendency to sleep walk. But, it is unclear whether this was the case during the attack. Some may voluntarily expose themselves to risk factors while others may not. Therefore improving our understanding of sleep walking is essential to establish whether individuals can be held responsible for behaviour.

Both Broughton and Lecendreux research focused on the assumption that sleep walking has a biological cause and both can be argued to have found evidence for such an assumption. However, through such research it is suggested environment plays a role too. Explaining sleep walking through purely biological means is reductionis and fails to explain the complex nature of sleep walking that occurs through the interaction of genes and the environment. Also such explanations do not consider the role of free will,therefore argued to be deterministic. However, if certain environmental stressors increase sleep walking occurrence, by controlling environmental factors we can reduce incidents of sleep walking, even with genetic vulnerabilities helping us to gain further understanding of sleep walking as a disorder.