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Sleep medicine is relevant in both neurology and general medicine. A disordered sleep–wake cycle can have major effects on many common neurological complaints such as headache and epilepsy, and it may also directly affect important general health issues, such as blood pressure. Furthermore, sleep related disorders such as parasomnias, particularly with agitation, can be hazardous to patients and bed partners while also being diagnostic clues in some neurodegenerative diseases.
The traditional view that sleep is simply the absence of wakefulness has been increasingly refined over the past 50 years or so. Rather, it is a precisely orchestrated and complex state with distinct and mutually exclusive phases: non-rapid eye movement (stages 1–4) and rapid eye movement sleep (non-REM and REM sleep, respectively), defined largely by the surface EEG. In a typical night, there are 4–5 cycles of non-REM and REM sleep (figure 1). In REM sleep, the cortical EEG is highly activated in common with wakefulness, usually corresponding to the vivid dreaming that accompanies REM sleep. REM sleep periods predominate towards the end of the nocturnal sleep period whereas the deepest stages of non-REM sleep (stages 3 and 4) tend to occur within an hour of sleep onset.
Normal versus abnormal
Given the normal variation in sleep patterns and habits between people, distinguishing whether or not a sleep related symptom suggests a formal disorder can be difficult. It is a salutary fact that normal ageing is associated with deteriorating and poorly consolidated nocturnal sleep.
▶. At least six EEG arousals per night, shown by intrusions of α rhythm on …
Competing interests None.
Provenance and peer review Commissioned; externally peer reviewed.