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Scientific Research

1. The Divine mystery
2. Sleep laboratories
3. Five cycles
4. Not temporary death

Sleep is a digestion of sensory impressions.
Novalis, German poet 18 th century

1. The Divine mystery

Sleep as a science in fact is relatively young. Before the nineteenth century, sleep rather was a divine mystery that was not to be discussed. No other scientific findings were communicated apart from the observation that sleep was induced by too lavish a dinner or the alchemists’ guesses that body juices and vapors cause sleep and that a lack of sleep has the brain dry up.

What makes us sleep, how we sleep and what happens inside the body during our sleep was only examined scientifically on the occasion of the first electrophysiological studies. Only since the first half of the previous century, physiologists, biochemists and neuropsychiatrists search for answers to questions such as what makes a bad sleeper sleep and why do we have to sleep.

Fifty years of study indeed provided barbiturates, benzodiazepines and non-benzodiazepine hypnotics, but unfortunately the ideal sleeping tablet was not found yet. What makes us sleep? What happens in our dreams? We do not know yet. What we actually do know today is what happens with our body during our sleep and to what sleep deficiency can lead.

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2. Sleep laboratories

Since professor Nathaniel Kleitman, a physiology professor at the University of Chicago, recorded the different brain waves during our sleep by means of an electro-encephalogram, at the same time measured our muscle tensions with an electro-myogram and recorded the eye movements with an electro-oculogram during the REM sleep, our sleep pattern can be printed and compared. In sleep labs, test sleepers were put to sleep with these 3 measuring devices and the results were examined.

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3. Five cycles

A polysomnography learns that we are still very active while we sleep. For persons who sleep from 11 o’clock in the evening until 7 o’clock in the morning, this activity can be divided in 5 different cycles that each last for about an hour and a half. These cycles differ as regards content and can be divided into several stages. The stages are mainly characterized by the deep sleep, the REM sleep (Rapid Eye Movement), the dream sleep and the non-restoring wake sleep.

A normal adult sleep, without internal or external disturbing factors, approximately gives the following image:

First cycle: we fall asleep

stage 1	we are no longer conscious of our environment
stage 2	(11:00pm-12:30am) we sink in a deeper sleep, muscles are relaxed
stage 3	deeper sleep brain waves have a lower frequency and a higher amplitude electro-myogram inactive
stage 4	deep sleep with alpha waves frequency 10 hertz and amplitude 50 microvolt electro-myogram inactive
REM sleep	Rapid Eye Movement electro-oculogram measures eye movements very short transition to beta brain waves with high frequency and small amplitude

Second cycle (12:30am-02:00am)

stage 1	skeleton muscles active, turning over possible, electro-myogram active
stage 2	muscle relaxation and transition to
stage 3	deeper sleep, no muscle tension
stage 4	deeper sleep, no muscle tension
REM sleep	somewhat longer than during the 1st cycle

Third cycle

stage 1	active electro-myogram, turning over
stage 2	somewhat longer to reach deep sleep
stage 3	less deep sleep, no muscle tension
stage 4	is hardly or no longer reached
REM sleep	much more REM sleep, no muscle tension

Fourth cycle

stage 1	active muscles, turning over, more alert to stimuli
stage 2
stage 3	we hardly reach this stage
stage 4	we no longer reach this stage REM highly active beta waves skeleton muscular paralysis dominates the fourth cycle

Fifth cycle (05:00am-07:00am)

stage 1	muscle tensions build up, more active turning over, alert to stimuli
stage 2	is hardly reached
stage 3	is hardly reached
stage 4
REM	complete skeleton muscular paralysis dominates this cycle; awaking

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4. Not temporary death

It has to be noticed that the deep sleep decreases around daybreak while the REM dream sleep increases. It also has to be noticed that there is no muscle tension during deep sleep and dream sleep.

Scientists distinguish REM sleep and non-REM sleep and found that 80% of our sleep can be classified as non-REM sleep and 25% of this non-REM sleep is deep sleep. A higher frequency and lower amplitude in the brain waves point to very strong brain activity, as during daytime. The lower alpha waves point to another type of brain activity.

Therefore, sleeping is not as being temporarily death. On the contrary, it is an active process during which we continue to see, hear and feel, but then at a much lower level. What does sleep science know about this deep sleep and our REM sleep? Why are these two kinds of sleep so important for our health?

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