Impact on sleep/wake system
Sleep is divided into five stages: stages 1, 2, 3, 4 and REM
(rapid eye movement) sleep. The time spent in each stage is
controlled by an “internal” clock, called the circadian
rhythm.
Normally, when an individual falls asleep, he first enters stage 1
sleep (the lightest stage) and progresses through stages 2 and 3 to
stage 4 (the deepest stage). Those 4 stages make up the non-rapid
eye movement (NREM) sleep. After about 90 minutes, the individual
swings from the NREM sleep to the REM (rapid eye movement) sleep.
In REM sleep, the brain is more active and the eyes of the sleeper,
which are usually quite still, begin to move in a rapid and jerky
manner while the muscles become temporarily paralyzed. The REM
sleep is also the stage of sleep during which people
dream.
In narcolepsy patients, the length and order of sleep stages is
disrupted. Untreated patients have REM sleep at evening sleep onset
instead of after a period of NREM sleep. They also have shorter
stage 3 and 4 sleep, resulting in less restorative nights.
Also, some of the characteristics of REM stage (lack of muscle
tone, vivid dreams) can intrude even during waking hours, provoking
for instance cataplexy attacks or hallucinations
The pictures below represent polysomnography (PSG) of both an
individual with normal sleep patterns and an untreated narcoleptic
patient. A polysomnography is an electroencephalogram during which
a number of physiologic variables are measured and recorded during
sleep.
Graph legend: MT = movement time; W = wake state; REM =
REM/paradoxal sleep; 1, 2, 3 and 4 = stages 1, 2, 3 and 4 of
sleep.
24-hour PSG recordings of a normal person
24-hour PSG recordings of an untreated narcolepsy patient
