A narcoleptic will fall asleep suddenly without warning throughout the day. They might also experience hallucinations and sleep paralysis. Narcolepsy affect 0.02-0.06% of the population, with most developing the condition in early adulthood.
REM – One of the first explanations of narcolepsy put forward said it is caused by a problem with the system the controls REM sleep.
HLA – HLA (human leukocyte antigens) are a component of the immune system. Hone et al (1983) found an increase frequency of one type of HLA, suggesting a link between the immune system and narcolepsy.
Hypocretin – Hypocretin is a neurotransmitter which is believed to help the body maintain wakefulness. Lin et al (1999) found a mutation of the gene corresponding to the processing of Hypocretin on dogs with narcolepsy, suggesting a lack of Hypocretin could be a cause of narcolepsy.
Opposing arguments – all the explanations about are biologically grounded. However, Lehrman and Weiss suggested that sudden attacks of sleepiness disguise sexual fantasies, and narcolepsy was a psychological issue rather than biological.
Research in the narcolepsy-HLA link – Research has found that the specific HLA variant which is believed to cause narcolepsy is also common in the general population, so it can be the only cause of narcolepsy (Mignot et al 1997).
Hypocretins – The link between hypocretins and narcolepsy that was found in dogs (Lin et al) has also been found in humans, suggesting it could well be a cause of narcolepsy.
Sleep walking is associated with stages 3 and 4 of sleep. It affects around 20% of children but less than 3% of adults.
Incomplete arousal – EEG recordings have found that both delta waves (normal in SWS) and beta waves (normal in the awake state) are present during sleep walking episodes.
Factors – There are several factors that can explain why this incomplete arousal might occur:
- Sleep deprivation
- Stress or anxiety
- Some drugs, e.g. anti-psychotics