Explanations for disorders of sleep
Insomnia is not defined in terms of number of hours of sleep a person has because there are large individual differences in the amount of sleep that is 'normal' for each person. Insomnia may involve problems falling asleep (intial insomnia), remaining asleep (middle insomnia) or waking up too early (terminal insomnia). Insomnia is classified as either transient (short term), intermittent (occasional) or chronic when it is more constant and long term (having occurred for one month or more).
Explanations of insomnia
Secondary insomnia is where there is a single, underlying medical, psychiatric or environmental cause. In such cases insomnia is a symptom of the main disorder, i.e. it is secondary. For example, insomnia is a characteristic symptom of illness such as depression or heart disease. It is also typical of peope who do shift work or who have circadian rhythm disordrs such as delayed sleep phase disorder. Insomnia may also be the result of environmental factors, such as too much caffeine (coffee, tea or even chocolate) or alcohol.
Primary insomnia describes cases where insomnia simply occurs on its own, with no known physical cause, for more than one month (DSM). In such cases insomnia is the person's primary problem. The individual may be feeling stressed or depressed, but such psychological states are not the problem - the insomnia is the problem. It may be that the individual has developed bad sleep habits (e.g. staying up late, sleeping in a room that is too light) and this has created insomnia, but insomnia is the problem. Sometimes insomnia may have had an identifiable cause but this has disappeared, yet the insomnia persists because of an expectation of sleep difficulty.
Sleepwaling (SW) is a disorder which is most common in childhood, affecting about 20% of children and less than 3% of adults (Hublin et al 1997). SW occurs only during NREM/SWS sleep and is related to night terrors, which are also only found in NREM sleep. A sleepwalker is not conscious and later has no memory for events during SW.
Explanations of sleepwalking
Incomplete arousal EEG recordings made during SW show a mixture of the delta waves which are typical of SWS plus the high frequency beta waves which are characteristic of the awake state. It looks as if SW occurs when a person in deep sleep is awakened but the arousal of the brain is incomplete. It is likely that this abnormal arousal is genetic.
Why is it common in childhood? One possibility is that it happens because children have more SWS than adults. Alternatively, Oliviero (2008) suggests that the GABA system that normally inhibits motor activity in SWS is not sufficiently developed in some children, and it also maybe underdeveloped in some adults. Insufficient amounts of GABA leave the motor neurons capable of commanding the body to move eben during sleep. Oliviero et al (2007) indeed found that adult sleepwalkers had signs of immaturity in the relevant neural circuits when compared…